What’s New

Request an Appointment

“Dropping Acid” Blog

Paradoxical Vocal Fold Movement

DIFFERENTIAL DIAGNOSIS OF PARADOXICAL VOCAL FOLD MOVEMENT

Key words: Stridor, paradoxical vocal fold movement, paradoxical vocal cord movement, vocal cord dysfunction, laryngeal dystonia, spasmodic dysphonia, Chiari malformations, phenothiazines, respiratory type dystonia, psychogenic stridor, airway obstruction, laryngospasm, laryngopharyngeal reflux, gastroesophageal reflux

ABSTRACT

Paradoxical vocal fold movement (PVFM) is an uncommon and sometimes confusing condition that affects the larynx. PVFM occurs when there is inappropriate adduction of the vocal folds during inspiration, and the resultant respiratory obstruction may be intermittent or continuous, mild or severe, depending on the cause. The etiologies of PVFM include inflammatory, neurological, neoplastic, iatrogenic, and psychological causes. This article presents the differential diagnosis of PVFM and clinical features that distinguish its various causes. In addition, paroxysmal laryngospasm is presented and discussed in relation to PVFM. [Word count 87]

Introduction

During the respiratory cycle of most higher animals and human beings, the vocal folds partially abduct with inhalation and partially adduct with exhalation.1 This phasic vocal fold movement is physiologic, and it allows the unimpeded movement of air into the lungs during inspiration while helping to maintain the alveolar patency of the lungs by providing positive airway pressure during expiration.

Some patients who present with dyspnea, stridor, and airway obstruction have paradoxical vocal fold movement (PVFM), characterized by inappropriate adduction of the vocal folds during inspiration.1-17 The persistence and the degree of inappropriate glottal closure with PVFM determines the degree of obstruction. In some patients, the problem is constant and severe requiring airway management, and in others the problem is intermittent and relatively mild. In addition to PVFM, patients may experience similar acute-onset symptoms due to laryngospasm (LS).

In the past, PVFM sometimes fell under the non-specific diagnosis of vocal cord dysfunction (VCD).2 In 1997, Maschka et al. provided a classification of PVFM9; herein, we offer an outline of the differential diagnosis and provide an approach to establishing a precise diagnosis.

DIFFERENTIAL DIAGNOSIS OF PVFM

Reactive upper airway obstruction virtually always occurs at the laryngeal level; while asthma is the most common reactive lower airway disease. Sometimes tracheal diseases, such as tracheomalacia, intrinsic or extrinsic neoplastic laryngotracheal growths (e.g., subglottic stenoses, carcinoid tumors, cancer, thyroid tumors), and bronchial/pulmonary diseases (e.g., asthma, COPD) may be mistaken for reactive upper airway disease.16,23-27

The pattern of stridor is the key differentiating factor between upper and lower airway obstruction. Stridor (noisy breathing) can be inspiratory, expiratory, or both (bi-phasic). Patients with LS and PVFM have inspiratory stridor, and asthma patients have expiratory stridor (wheezing).

Many LS and PVFM patients present with self-described “choking” episodes, but the term may be used to describe several different symptoms. “Choking” can be used to describe: (1) dysphagia, i.e., food getting stuck in the hypopharynx or esophagus, (2) aspiration, e.g., saliva, liquid, food, or some other foreign body getting into the airway, usually stimulating violent coughing, or (3) acute-onset breathing problems, such as stridor.

As a rule, LS patients complain of choking episodes, while PVFM patients often (mistakenly) call their symptom “asthma.” And indeed, the differences between LS, PVFM, and asthma are sometimes indistinct as laryngopharyngeal reflux (LPR) can be associated with all three problems.8,15-18,21-23,25-27 There are typical differences, the single most important of which is that during attacks of LS, the vocal folds simply do not open; whereas with the latter, there is vocal fold movement, albeit reduced and paradoxical. LS is paroxysmal, acute-onset, associated with severe airway obstruction and inspiratory stridor, and not infrequently with a variety of LPR symptoms26-31; see Table 1. PVFM is less common than LS, and its differential diagnosis is shown in Table 2.

Laryngopharyngeal Reflux (LPR)

LPR is the most common cause of PVFM. Reflux-related PVFM and LS are usually intermittent, typically lasting minutes to hours (sometimes days), and not usually requiring airway intervention. The respiratory obstruction seen with LS and PVFM are believed to be related to stimulation of vagally-mediated reflexes by exposure of gastric fluids to laryngopharyngeal (supraglottic) chemoreceptors.19-22 It has been shown in an animal model that the afferent limb of the LS reflex is innervated by the superior laryngeal nerves and that the efferents are innervated by the recurrent laryngeal nerves.21,22 The LS reflex is crossed, that is, afferent stimulation of one side results in bilateral efferent responses.22

Patients with LPR-related PVFM usually have other clues that they have LPR. Often the attacks follow a pattern, e.g., occurring after a meal, after the start of exercise, or after bending over. Sometimes the attacks may awake the patient from sound sleep. Other times the attacks occur without any pattern or identifiable precipitant, but the patient may have symptoms and laryngeal findings of LPR.26-29 Some patients have several attacks each day, while others have as few as one or so a year.

LPR is often silent, occurring without heartburn. Only about 30% of LPR patients report ever having heartburn.26,29 However, LPR patients do complain of symptom(s), such as chronic or intermittent hoarseness, difficulty swallowing, a sensation of a lump in the throat (globus pharyngeus), chronic throat clearing and cough, and/or “post-nasal drip.”26,29-31

Loughlin et al.18 reported clinical data from 15 consecutive patients with PVFM, twelve of whom underwent ambulatory, 24-hour, double-probe (simultaneous esophageal and pharyngeal) pH monitoring. Almost all (11/12) were positive for LPR. All of the patients were treated with dietary and lifestyle modification as well as twice-daily proton pump inhibitors; and within four weeks, all attacks of laryngospasm had ceased in all 15 patients.18 H2-antagonists appear to be inadequate treatment for LPR in this group.26,29 Long-term, high-dose medical treatment with proton pump inhibitors is usually necessary26,29; and for some with LPR, antireflux surgery (fundoplication) should be considered as an alternative to medical treatment, especially for medical treatment failures.32,33

Respiratory-Type Adductor Laryngeal Dystonia

After LPR, respiratory-type laryngeal dystonia appears to be the second most common cause of PVFM. (We see approximately 2-3 such cases a year.) Nevertheless, this is a relatively unusual manifestation of dystonia. The most common laryngeal dystonia causes spasmodic dysphonia (SD). It occurs in women more frequently than in men; it is rarely seen in people under age 20 years; it may affect the voice severely; and respiration is usually unaffected. Blitzer and Brin reported a large series of patients with laryngeal dystonia, most of whom had the well-recognized adductor-type SD; only 1% had a respiratory-type of adductor laryngeal dystonia.34

The diagnosis of respiratory-type dystonia depends upon the medical history and laryngeal findings. First, the history will reveal that the patient has continual breathing problems of varying degrees in the daytime but not during sleep. This is similar to other task-specific dystonias like SD, that is, symptoms disappear during sleep. Second, during transnasal flexible laryngoscopy (TFL), the examiner will almost always see some degree of PVFM. Indeed, patients with a neurogenic etiology are expected to have more continuous symptoms than patients with other PVFM causes. Treole et al. reported that inappropriate vocal fold adduction during inspiration was observed in some symptomatic as well as asymptomatic PVFM cases.11 Third, during TFL, when the patient is asked to “take a deep breath,” the paradoxical adductions will worsen. Finally, this group of patients responds dramatically to treatment (vocal fold injections) with Botulinum toxin A (Botox).

Drug-Induced (Laryngeal) Dystonic Reactions

Temporary drug-induced PVFM has been reported after administration of neuroleptic drugs such as phenothiazines, including chlorpromazine and haloperidol.35 This cause of PVFM needs to be considered in patients receiving such medications. In these cases, the drug-induced stridor is often associated with extrapyramidal symptoms, muscle stiffness, and movement disorders of the head and neck, e.g., torticollis. The airway obstruction (PVFM) and the other symptoms are relatively short-lived (hours) and are reversible with intravenous administration of an anticholinergic drugs.36

PVFM may also seen in association with general anesthesia (especially postoperatively); it appears to be associated with phenothiazine and Thiopental use.36 Anesthesia-related, drug-induced PVFM may explain some cases of “prolonged laryngospasm” that may be observed during emergence from anesthesia. Finally, it has been shown experimentally that such laryngospasm can be prevented by the administration of topical lidocaine.

Asthma-Associated PVFM

As mentioned above, patients who present with PVFM are frequently misdiagnosed as having asthma as the cause of their airway obstruction, even though anti-asthma medications are ineffective. Nevertheless, there appears to be a small subset of patients with asthma who also do have PVFM.6,24,25 Although the mechanism of PVFM in these patients is unknown, glottal aperture changes have been observed in asthma patients24; and vagal reflex dysfunction may be the cause. In any asthma patient, when inspiratory stridor is present, the diagnosis of PVFM should be considered, and the finding of PVFM on TFL is diagnostic.

Brainstem Abnormalities

Central neurological (usually brainstem) abnormalities can cause PVFM, in addition to or complicated by bilateral abductor paralysis, apneic episodes, and central sleep apnea syndrome.37,38 Severe closed head injury, Chiari malformations I and II, meningomyelocele, and cerebrovascular accidents (strokes of the posterior circulation) may all produce PVFM. In these cases, the obstruction and inappropriate vocal fold movement may be inconsistent and variable, or it may not change with multiple laryngeal examinations. Typically, the stridor does not disappear during sleep. This point of differentiation is important, since with other causes of PVFM, the stridor is paroxysmal or improves during sleep (excluding LPR-related LS that may occur at night during sleep). In addition, most patients with PVFM due to central neurological disease have significant airway obstruction and other neurological deficits.37,38

Early (days or weeks) after closed head injury, extubation may fail and the patient may require multiple intubations, and then, later on, a tracheotomy. With time, as the cerebral and brainstem edema subsides, the vocal fold movement may return to normal and the stridor may disappear. Similarly, some patients with congenital lesions of the brainstem may experience a normalization of vocal fold function after surgical treatment of the lesion.38

Psychogenic Stridor

Many of the authors’ PVFM patients were referred to us with this diagnosis, but in our experience, psychogenic PVFM is uncommon. Typically, with psychogenic PVFM, the respiratory symptoms occur with a sudden onset and a sudden offset. In addition, such patients are often relatively unconcerned (blasé) about their noisy breathing and airway obstruction; and they may have a psychiatric history or obvious secondary gain.39 Some may casually ask to have a tracheotomy performed.

Psychogenic PVFM patients usually have inconsistent laryngeal findings on TFL, and the clinician can fool the patient during the examination, making the PVFM go away. Sometimes the patient will display bizarre laryngeal behaviors in an attempt to consistently maintain the stridor during sniffing (that usually causes reflexive vocal fold hyperabduction). Also, if the patient is asked to read a long passage aloud, the stridor may disappear and phasic respiratory activity of the vocal folds may become normal. Finally, in the past, we have been able to precipitate and ameliorate PVFM in some such patients by injections of placebo.40

A word of caution about this diagnosis. Even though the criteria for psychogenic stridor are more-or-less established — (1) periods of normal phasic vocal fold movement during the laryngoscopic examination, (2) induction of stridor and response to placebo, and (3) a psychological or psychiatric disorder — this is almost a diagnosis of exclusion. A review of the literature makes clear that many reported cases of “psychogenic stridor” probably actually had an organic basis, e.g., reflux or dystonia. Patients with presumed psychogenic PVFM should be approached by the otolaryngologist, the speech-language pathologist, and the psychologist and/or psychiatrist as a team, and should be completely evaluated before the team reaches that diagnosis.

DIAGNOSTIC APPROACH TO THE PATIENT WITH PVFM

The medical history of a patient with difficulty breathing, stridor, or choking episodes should be meticulously obtained so that the clinician knows the pattern and character of the problem. The following are key questions when taking the medical history:

  1. If there is stridor, is it constant or intermittent?
  2. Is the breathing problem during inspiration or expiration?
  3. What is the frequency, duration, and severity of the attacks?
  4. Are there any activities or behaviors that precipitate the attacks?
  5. Are there nighttime attacks; do they wake the patient from sleep?
  6. Is there any history of head trauma, stroke, or brainstem problem?
  7. Are there any other associated symptoms, such as hoarseness, dysphagia, globus pharyngeus, or cough?

These questions can quickly limit the diagnostic possibilities in each case. In fact, if they are clearly presented and answered, the clinician should suspect the diagnosis before even attempting the laryngeal examination. Most patients with LS and PVFM clearly state that during attacks they have more trouble breathing in than out and that they have audible inspiratory stridor. In the case of PVFM, pattern identification is invaluable in diagnosis; see Table 3.

After the medical history is obtained, the first examination of the patient should be TFL. Per oral examination methods, especially when the tongue of the patient is grasped, are almost useless in the diagnosis of PVFM, which is usually diagnosed by laryngoscopy. The diagnosis should be considered when there are findings of: (1) inappropriate vocal fold adduction during inspiration (>50% medialization but less than full closure), (2) paroxysmal inability to abduct the vocal folds (“transient abductor paralysis”), or (3) a combination of these findings. A number of laryngeal findings have been reported in the literature, including a posterior glottal chink during inspiration2 and expiration,6,10 and when symptomatic and asymptomatic.11

There is one group of patients that comprises a notable exception. Patients with LPR-induced paroxysmal LS may have normal phasic vocal fold movement during some examinations. However, these patients have other findings characteristic of LPR (edema, erythema, posterior commissure hypertrophy, and granulation).

During TFL, the patient is asked to: (1) alternatively phonate the vowel /i/ and sniff, in rapid alternating succession, (2) take fast, deep breaths, (3) cough, throat clear, or chuckle, followed by a deep breath, (4) count to fifty, rapidly and loudly, (5) read a written passage in a loud voice, and (6) sing. These maneuvers may reveal a pattern of adduction and abduction consistent with PVFM and a specific diagnosis.

Generally recommended in the work-up of a PVFM patient is pulmonary function testing, particularly to rule out asthma or other lower respiratory diseases. A truncated inspiratory limb of the flow-volume loop is typically observed with PVFM patients, but not with asthma patients.13 Murry et al. also reported a reduced ratio of forced inspiratory volume to forced inspiratory vital capacity for PVFM patients.15 Additional testing may be warranted depending on the suspected cause of PVFM. Such include serial laryngeal examinations by TFL, pH monitoring, neuropsychiatric evaluation, placebo injections, acoustic analysis, audio-recordings of the patient’s breathing during sleep, and radiographic examinations. In selected cases, therapeutic trials of antireflux medication or laryngeal injections of Botox may be indicated.

For reflux-induced PVFM, a firm diagnosis can be made when positive pH monitoring data are combined with the medical history and laryngeal findings of LPR. In addition, resolution of symptoms with a therapeutic trial of aggressive antireflux therapy may confirm the diagnosis.

The medical history can give important clues for patients suspected of having respiratory-type laryngeal dystonia. Unlike patients in the other PVFM groups, patients with respiratory-type laryngeal dystonia describe a progressive onset of the PVFM over a period weeks, months, or years. In addition, such patients usually deny having other symptoms. On occasion, differentiating dystonic from psychogenic PVFM can be a difficult task.

Except for patients in the brainstem abnormality group (who often require tracheotomy), patients with PVFM usually do not have respiratory obstruction severe enough to warrant emergency airway intervention. Of the other groups of patients with PVFM, dystonia patients appear next in terms of the frequency of need for airway support, followed by the psychogenic group, the asthma group, and the LPR group.

Regardless of the underlying cause, on the very first visit, PVFM patients require counseling and training (breathing recovery exercises) by a speech-language pathologist.15,17 We use the quick-sniff-slow-blow technique because it usually aborts PVFM and LS attacks. This type of intervention provides reassurance for fearful patients, and initiates the therapy program (that includes additional counseling, respiratory exercises that focus on exhalation and rhythmic abdominal movement patterns, and, in some cases, resonant voice and easy-onset voice exercises). The variety of techniques and duration of therapy is individualized according to the underlying cause of PVFM as well as the needs and responsiveness of each individual patient.

SUMMARY

PVFM presents the clinician with an interesting differential diagnosis. The causes of PVFM, in order of frequency of occurrence are: (1) laryngopharyngeal reflux (LPR), (2) respiratory-type laryngeal dystonia, (3) abnormalities of the brainstem, (4) brain injuries such as stroke and closed head injuries, and (5) psychogenic stridor. The work-up of PVFM requires a multidisciplinary approach and a variety of diagnostic methods. Likewise, treatment must be individualized. [Word count 2,645]

REFERENCES

  1. Ward PH, Hanson DG, Berci G. Observations on central neurologic etiology for laryngeal dysfunction. Ann Otol Rhinol Laryngol 1981;90:430-441.
  2. Christopher KL, Wood RP, Eckert RC, Blager FB, et al. Vocal-cord dysfunction presenting as asthma. NEJM 1983;308:1566-70.
  3. Patterson R, Schatz M, Horton M. Munchausen’s stridor: non-organic laryngeal obstruction. Clin Allergy 1974;4:307-310.
  4. Appleblatt KL, Baker SR. Functional airway obstruction. A new syndrome. Arch Otolaryngol 1981;107:305-307.
  5. Kellman RM, Leopold DA. Paradoxical vocal fold motion: an important cause of stridor. Laryngoscope 1982;92:58-60.
  6. Martin RJ, Blager FB, Gay ML, et al. Paradoxical vocal cord motion in presumed asthmatics. Semin Respir Crit Care Med 1987;8:332-8.
  7. George MK, O’Connell JE, Batch AJ. Paradoxical vocal fold motion: an unusual cause of stridor. J Laryngol Otol 1991;105:312-314.
  8. Koufman, JA. Paradoxical vocal cord movement. The Visible Voice 1994;3:49-53 & 70-71.
  9. Maschka DA, Bauman NM, McCray PB, Jr., Hoffman HT, et al. A classification scheme for paradoxical vocal cord motion. Laryngoscope 1997;107:1429-1435.
  10. Brugman SM, Simons SM. Vocal cord dysfunction: Don’t mistake it for asthma. The Physician and Sports Medicine 1998;26:63-74.
  11. Treole K, Trudeau MD, Forrest LA. Endoscopic and stroboscopic description of adults with paradoxical vocal fold dysfunction. J Voice 1999;13:143-52.
  12. Andrianopoulos MV, Gallivan GJ, Gallivan KH. PVCM, PVCD, EPL, and irritable larynx syndrome: what are we talking about and how do we treat it? J Voice 2000;14:607-18.
  13. Mathers-Schmidt BA. Paradoxical vocal fold motion: a tutorial on a complex disorder and the speech-language pathologist’s role. Am J Speech Lang Path 2001;10:111-25.
  14. Altman KW, Simpson CB, Amin MR, et al. Cough and paradoxical vocal fold motion. Otolaryngol Head Neck Surg 2002;127:501-511.
  15. Murry T, Tabaee A, Aviv J. Respiratory retraining of refractory cough and laryngopharyngeal reflux in patients with paradoxical vocal fold movement disorder. Laryngoscope 2004;114:1341-44.
  16. Patel NJ, Jorgensen C, Kuhn J, Merati AL. Concurrent laryngeal abnormalities in patients with paradoxical vocal fold dysfunction. Otolaryngol Head Neck Surg 2004;130:686-689.
  17. Murry T, Tabaee A, Owczarzak V, Aviv J. Respiratory retraining therapy and management of laryngopharyngeal reflux in the treatment of patients with cough and paradoxical vocal fold movement. Ann Otol Rhinol Laryngol 2006;115:754-58.
  18. Loughlin CJ, Koufman JA. Paroxysmal laryngospasm secondary to gastroesophageal reflux. Laryngoscope 1996;106:1502-1505.
  19. Henderson PS, Cohen JI, Jarnberg P-E, et al. A canine model for studying laryngospasm and its prevention. Laryngoscope 1992;102:1237-41.
  20. Bauman NM, Sandler AD, Schmidt C, et al. Reflex laryngospasm induced by stimulation of distal afferents. Laryngoscope 1994;104:209-14.
  21. Loughlin CJ, Koufman JA, Averill DB, et al. Acid-induced laryngospasm in a canine model. Laryngoscope 1996;106:1506-1509.
  22. Duke SG, Postma GN, McGuirt Jr. WF, et al. Laryngospasm and diaphragmatic arrest in the immature canine after laryngeal acid exposure: a possible model for sudden infant death syndrome (SIDS). Ann Otol Rhinol Laryngol 2001;110:729-733.
  23. Koufman JA. (Unpublished data 2005).
  24. Collett PW, Brancatisano T, Konno K. Changes in glottic aperture during bronchial asthma. Am Rev Respir Dis 1983;128:719-723.
  25. Harding SM, Richter JE. The role of gastroesophageal reflux in chronic cough and asthma. Chest 1997;111:1389-1402.
  26. Koufman JA. The otolaryngologic manifestations of gastroesophageal reflux disease (GERD): A clinical investigation of 225 patients using ambulatory 24-hour pH monitoring and an experimental investigation of the role of acid and pepsin in the development of laryngeal injury. Laryngoscope 1991;101 (Suppl. 53):1-78.
  27. Little JP, Matthews BL, Glock MS, et al. Extraesophageal pediatric reflux: 24-hour double-probe pH monitoring of 222 children. Ann Otol Rhinol Laryngol Suppl 1997;169:1-16.
  28. Belafsky PC, Postma GN, Koufman JA. The validity and reliability of the reflux finding score (RFS). Laryngoscope 2001;111:1313-1317.
  29. Koufman JA, Aviv JE, Casiano RR, Shaw GY. Position statement of the American Academy of Otolaryngology-Head and Neck Surgery on laryngopharyngeal reflux. Otolaryngol Head Neck Surg 2002;127:32-35.
  30. Belafsky PC, Postma GN, Koufman JA. Validity and reliability of the reflux symptom index (RSI). J Voice 2002;16:274-77.
  31. Carrau RL, Khidr A, Gold KF, et al. Validation of a quality-of-life instrument for laryngopharyngeal reflux. Arch Otolaryngol Head Neck Surg 2005;131:315-20.
  32. Amin MR, Postma GN, Johnson P, et al. Proton pump inhibitor resistance in the treatment of laryngopharyngeal reflux. Otolaryngol Head Neck Surg 2001;125:374-378.
  33. Westcott CJ, Hopkins MB, Bach KK, et al. Fundoplication for laryngopharyngeal reflux. J Amer Coll Surg 2004;199:23-30.
  34. Blitzer A, Brin MF. Laryngeal dystonia: a series with botulinum toxin therapy. Ann Otol Rhinol Laryngol 1991;100:85-89.
  35. Koek RJ, Pi EH. Acute laryngeal dystonic reactions to neuroleptics. Psychosomatics 1989;30:359-364.
  36. Stoelting RK. Pharmacology and Physiology in Anesthetic Practice. page 112, Philadelphia, J. B. Lippincott Co., 1987.
  37. Holinger PC, Holinger LD, Reichert TJ, Holinger PH. Respiratory obstruction and apnea in infants with bilateral abductor vocal fold paralysis, meningomyelocele, hydrocephalus, and Arnold-Chiari malformation. J Pediatrics 1978;92:368-373.
  38. Charney EB, Rorke LB, Sutton LN, Schut L. Management of Chiari II complications in infants with meningomyelocele. J Pediatrics 1987;111:364-371.
  39. Snyder HS, Weiss E: Hysterical stridor: a benign cause of upper airway obstruction. Ann Emer Med 1989;18:991-994.
  40. Walker FO, Koufman JA. Induction of psychogenic respiratory distress. (Unpublished data).

TABLE 1

TYPICAL DIFFERENTIATING FEATURES OF LARYNGOSPASM (LS) AND PARADOXICAL VOCAL FOLD MOVEMENT (PCVM)

HISTORY & SYMPTOMS LS PVFM
Duration of attacks Minutes Hours
Sudden (acute) onset Yes Sometimes
Stridor at rest during attacks Yes Sometimes
Associated cough and hoarseness Usually Sometimes

LARYNGEAL EXAMINATION

Findings of laryngopharyngeal reflux Yes Sometimes
Adductions during inspiration No Usually
Brisk abduction with sniffing Yes Usually
Failure of any abduction during attacks Yes No

TABLE 2

DIFFERENTIAL DIAGNOSIS OF PARADOXICAL VOCAL FOLD MOVEMENT

  • Laryngopharyngeal reflux (LPR)
  • Respiratory-type laryngeal dystonia
  • Drug-induced laryngeal dystonic reactions
  • Asthma-associated laryngeal dysfunction
  • Psychogenic stridor (usually in adolescents)
  • Abnormalities that affect the brainstem
    • Chiari malformation I & II, hydrocephalus, meningomyelocele, cerebrovascular accident (stroke),closed head injury

TABLE 3

DIFFERENTIATING FEATURES OF THE DIFFERENT CAUSESOF PARADOXICAL VOCAL FOLD MOVEMENT

Pattern Duration Dysphonia Airway Support
Reflux Paroxysmal Minutes-hours Usually Almost never
Dystonia Daytime Hours Rarely Sometimes
Drug Induced Continual Hours-days Rarely Sometimes
Psychogenic Paroxysmal Variable Never Sometimes
Brainstem Continual Continual Sometimes Usually

DIFFERENTIAL DIAGNOSIS OF PARADOXICAL VOCAL FOLD MOVEMENT

ABSTRACT

Paradoxical vocal fold movement (PVFM) is an uncommon and sometimes confusing condition that affects the larynx. PVFM occurs when there is inappropriate adduction of the vocal folds during inspiration, and the resultant respiratory obstruction may be intermittent or continuous, mild or severe, depending on the cause. The etiologies of PVFM include inflammatory, neurological, neoplastic, iatrogenic, and psychological causes. This article presents the differential diagnosis of PVFM and clinical features that distinguish its various causes. In addition, paroxysmal laryngospasm is presented and discussed in relation to PVFM.

INTRODUCTION

During the respiratory cycle of most higher animals and human beings, the vocal folds partially abduct with inhalation and partially adduct with exhalation.1 This phasic vocal fold movement is physiologic, and it allows the unimpeded movement of air into the lungs during inspiration while helping to maintain the alveolar patency of the lungs by providing positive airway pressure during expiration.

Some patients who present with dyspnea, stridor, and airway obstruction have paradoxical vocal fold movement (PVFM), characterized by inappropriate adduction of the vocal folds during inspiration.1-17 The persistence and the degree of inappropriate glottal closure with PVFM determines the degree of obstruction. In some patients, the problem is constant and severe requiring airway management, and in others the problem is intermittent and relatively mild. In addition to PVFM, patients may experience similar acute-onset symptoms due to laryngospasm (LS).18-22

In the past, PVFM sometimes fell under the non-specific diagnosis of vocal cord dysfunction (VCD).2 In 1997, Maschka et al. provided a classification of PVFM9; herein, we offer an outline of the differential diagnosis and provide an approach to establishing a precise diagnosis.

DIFFERENTIAL DIAGNOSIS OF PVFM

Reactive upper airway obstruction virtually always occurs at the laryngeal level; while asthma is the most common reactive lower airway disease. Sometimes tracheal diseases, such as tracheomalacia, intrinsic or extrinsic neoplastic laryngotracheal growths (e.g., subglottic stenoses, carcinoid tumors, cancer, thyroid tumors), and bronchial/pulmonary diseases (e.g., asthma, COPD) may be mistaken for reactive upper airway disease.16,23-27

The pattern of stridor is the key differentiating factor between upper and lower airway obstruction. Stridor (noisy breathing) can be inspiratory, expiratory, or both (bi-phasic). Patients with LS and PVFM have inspiratory stridor, and asthma patients have expiratory stridor (wheezing).
Many LS and PVFM patients present with self-described “choking” episodes, but the term may be used to describe several different symptoms. “Choking” can be used to describe: (1) dysphagia, i.e., food getting stuck in the hypopharynx or esophagus, (2) aspiration, e.g., saliva, liquid, food, or some other foreign body getting into the airway, usually stimulating violent coughing, or (3) acute-onset breathing problems, such as stridor.

As a rule, LS patients complain of choking episodes, while PVFM patients often (mistakenly) call their symptom “asthma.” And indeed, the differences between LS, PVFM, and asthma are sometimes indistinct as laryngopharyngeal reflux (LPR) can be associated with all three problems.8,15-18,21-23,25-27 There are typical differences, the single most important of which is that during attacks of LS, the vocal folds simply do not open; whereas with the latter, there is vocal fold movement, albeit reduced and paradoxical. LS is paroxysmal, acute-onset, associated with severe airway obstruction and inspiratory stridor, and not infrequently with a variety of LPR symptoms26-31; see Table 1. PVFM is less common than LS, and its differential diagnosis is shown in Table 2.

TABLE 1
TYPICAL DIFFERENTIATING FEATURES OF LARYNGOSPASM (LS)
AND PARADOXICAL VOCAL FOLD MOVEMENT (PCVM)

LS PVFM
HISTORY & SYMPTOMS
Duration of attacks Minutes Hours
Sudden (acute) onset Yes Sometimes
Stridor at rest during attacks Yes Sometimes
Associated cough and hoarseness Usually Sometimes
LARYNGEAL EXAMINATION
Findings of laryngopharyngeal reflux Yes Sometimes
Adductions during inspiration No Usually
Brisk abduction with sniffing Yes Usually
Failure of any abduction during attacks Yes No

TABLE 2
DIFFERENTIAL DIAGNOSIS OF PARADOXICAL VOCAL FOLD MOVEMENT

• Laryngopharyngeal reflux (LPR)
• Respiratory-type laryngeal dystonia
• Drug-induced laryngeal dystonic reactions
• Asthma-associated laryngeal dysfunction
• Psychogenic stridor (usually in adolescents)
• Abnormalities that affect the brainstem

Chiari malformation I & II, hydrocephalus, meningomyelocele, cerebrovascular accident (stroke),
closed head injury

Laryngopharyngeal Reflux (LPR)

LPR is the most common cause of PVFM. Reflux-related PVFM and LS are usually intermittent, typically lasting minutes to hours (sometimes days), and not usually requiring airway intervention. The respiratory obstruction seen with LS and PVFM are believed to be related to stimulation of vagally-mediated reflexes by exposure of gastric fluids to laryngopharyngeal (supraglottic) chemoreceptors.19-22 It has been shown in an animal model that the afferent limb of the LS reflex is innervated by the superior laryngeal nerves and that the efferents are innervated by the recurrent laryngeal nerves.21,22 The LS reflex is crossed, that is, afferent stimulation of one side results in bilateral efferent responses.22

Patients with LPR-related PVFM usually have other clues that they have LPR. Often the attacks follow a pattern, e.g., occurring after a meal, after the start of exercise, or after bending over. Sometimes the attacks may awake the patient from sound sleep. Other times the attacks occur without any pattern or identifiable precipitant, but the patient may have symptoms and laryngeal findings of LPR.26-29 Some patients have several attacks each day, while others have as few as one or so a year.

LPR is often silent, occurring without heartburn. Only about 30% of LPR patients report ever having heartburn.26,29 However, LPR patients do complain of symptom(s), such as chronic or intermittent hoarseness, difficulty swallowing, a sensation of a lump in the throat (globus pharyngeus), chronic throat clearing and cough, and/or “post-nasal drip.”26,29-31

Loughlin et al.18 reported clinical data from 15 consecutive patients with PVFM, twelve of whom underwent ambulatory, 24-hour, double-probe (simultaneous esophageal and pharyngeal) pH monitoring. Almost all (11/12) were positive for LPR. All of the patients were treated with dietary and lifestyle modification as well as twice-daily proton pump inhibitors; and within four weeks, all attacks of laryngospasm had ceased in all 15 patients.18 H2-antagonists appear to be inadequate treatment for LPR in this group.26,29 Long-term, high-dose medical treatment with proton pump inhibitors is usually necessary26,29; and for some with LPR, antireflux surgery (fundoplication) should be considered as an alternative to medical treatment, especially for medical treatment failures.32,33

Respiratory-Type Adductor Laryngeal Dystonia

After LPR, respiratory-type laryngeal dystonia appears to be the second most common cause of PVFM. (We see approximately 2-3 such cases a year.) Nevertheless, this is a relatively unusual manifestation of dystonia. The most common laryngeal dystonia causes spasmodic dysphonia (SD). It occurs in women more frequently than in men; it is rarely seen in people under age 20 years; it may affect the voice severely; and respiration is usually unaffected. Blitzer and Brin reported a large series of patients with laryngeal dystonia, most of whom had the well-recognized adductor-type SD; only 1% had a respiratory-type of adductor laryngeal dystonia.34

The diagnosis of respiratory-type dystonia depends upon the medical history and laryngeal findings. First, the history will reveal that the patient has continual breathing problems of varying degrees in the daytime but not during sleep. This is similar to other task-specific dystonias like SD, that is, symptoms disappear during sleep. Second, during transnasal flexible laryngoscopy (TFL), the examiner will almost always see some degree of PVFM. Indeed, patients with a neurogenic etiology are expected to have more continuous symptoms than patients with other PVFM causes. Treole et al. reported that inappropriate vocal fold adduction during inspiration was observed in some symptomatic as well as asymptomatic PVFM cases.11 Third, during TFL, when the patient is asked to “take a deep breath,” the paradoxical adductions will worsen. Finally, this group of patients responds dramatically to treatment (vocal fold injections) with Botulinum toxin A (Botox).

Drug-Induced (Laryngeal) Dystonic Reactions

Temporary drug-induced PVFM has been reported after administration of neuroleptic drugs such as phenothiazines, including chlorpromazine and haloperidol.35 This cause of PVFM needs to be considered in patients receiving such medications. In these cases, the drug-induced stridor is often associated with extrapyramidal symptoms, muscle stiffness, and movement disorders of the head and neck, e.g., torticollis. The airway obstruction (PVFM) and the other symptoms are relatively short-lived (hours) and are reversible with intravenous administration of an anticholinergic drugs.36
PVFM may also seen in association with general anesthesia (especially postoperatively); it appears to be associated with phenothiazine and Thiopental use.36 Anesthesia-related, drug-induced PVFM may explain some cases of “prolonged laryngospasm” that may be observed during emergence from anesthesia. Finally, it has been shown experimentally that such laryngospasm can be prevented by the administration of topical lidocaine.

Asthma-Associated PVFM

As mentioned above, patients who present with PVFM are frequently misdiagnosed as having asthma as the cause of their airway obstruction, even though anti-asthma medications are ineffective. Nevertheless, there appears to be a small subset of patients with asthma who also do have PVFM.6,24,25 Although the mechanism of PVFM in these patients is unknown, glottal aperture changes have been observed in asthma patients24; and vagal reflex dysfunction may be the cause. In any asthma patient, when inspiratory stridor is present, the diagnosis of PVFM should be considered, and the finding of PVFM on TFL is diagnostic.

Brainstem Abnormalities

Central neurological (usually brainstem) abnormalities can cause PVFM, in addition to or complicated by bilateral abductor paralysis, apneic episodes, and central sleep apnea syndrome.37,38 Severe closed head injury, Chiari malformations I and II, meningomyelocele, and cerebrovascular accidents (strokes of the posterior circulation) may all produce PVFM. In these cases, the obstruction and inappropriate vocal fold movement may be inconsistent and variable, or it may not change with multiple laryngeal examinations. Typically, the stridor does not disappear during sleep. This point of differentiation is important, since with other causes of PVFM, the stridor is paroxysmal or improves during sleep (excluding LPR-related LS that may occur at night during sleep). In addition, most patients with PVFM due to central neurological disease have significant airway obstruction and other neurological deficits.37,38

Early (days or weeks) after closed head injury, extubation may fail and the patient may require multiple intubations, and then, later on, a tracheotomy. With time, as the cerebral and brainstem edema subsides, the vocal fold movement may return to normal and the stridor may disappear. Similarly, some patients with congenital lesions of the brainstem may experience a normalization of vocal fold function after surgical treatment of the lesion.38

Psychogenic Stridor

Many of the authors’ PVFM patients were referred to us with this diagnosis, but in our experience, psychogenic PVFM is uncommon. Typically, with psychogenic PVFM, the respiratory symptoms occur with a sudden onset and a sudden offset. In addition, such patients are often relatively unconcerned (blasé) about their noisy breathing and airway obstruction; and they may have a psychiatric history or obvious secondary gain.39 Some may casually ask to have a tracheotomy performed.

Psychogenic PVFM patients usually have inconsistent laryngeal findings on TFL, and the clinician can fool the patient during the examination, making the PVFM go away. Sometimes the patient will display bizarre laryngeal behaviors in an attempt to consistently maintain the stridor during sniffing (that usually causes reflexive vocal fold hyperabduction). Also, if the patient is asked to read a long passage aloud, the stridor may disappear and phasic respiratory activity of the vocal folds may become normal. Finally, in the past, we have been able to precipitate and ameliorate PVFM in some such patients by injections of placebo.40

A word of caution about this diagnosis. Even though the criteria for psychogenic stridor are more-or-less established — (1) periods of normal phasic vocal fold movement during the laryngoscopic examination, (2) induction of stridor and response to placebo, and (3) a psychological or psychiatric disorder — this is almost a diagnosis of exclusion. A review of the literature makes clear that many reported cases of “psychogenic stridor” probably actually had an organic basis, e.g., reflux or dystonia. Patients with presumed psychogenic PVFM should be approached by the otolaryngologist, the speech-language pathologist, and the psychologist and/or psychiatrist as a team, and should be completely evaluated before the team reaches that diagnosis.

DIAGNOSTIC APPROACH TO THE PATIENT WITH PVFM

The medical history of a patient with difficulty breathing, stridor, or choking episodes should be meticulously obtained so that the clinician knows the pattern and character of the problem. The following are key questions when taking the medical history:
(1) If there is stridor, is it constant or intermittent?
(2) Is the breathing problem during inspiration or expiration?
(3) What is the frequency, duration, and severity of the attacks?
(4) Are there any activities or behaviors that precipitate the attacks?
(5) Are there nighttime attacks; do they wake the patient from sleep?
(6) Is there any history of head trauma, stroke, or brainstem problem?
(7) Are there any other associated symptoms, such as hoarseness, dysphagia, globus pharyngeus, or cough?

These questions can quickly limit the diagnostic possibilities in each case. In fact, if they are clearly presented and answered, the clinician should suspect the diagnosis before even attempting the laryngeal examination. Most patients with LS and PVFM clearly state that during attacks they have more trouble breathing in than out and that they have audible inspiratory stridor. In the case of PVFM, pattern identification is invaluable in diagnosis; see Table 3.

TABLE 3
DIFFERENTIATING FEATURES OF THE DIFFERENT CAUSES
OF PARADOXICAL VOCAL FOLD MOVEMENT

PATTERN DURATION DYSPHONIA AIRWAY SUPPORT
REFLUX Paroxysmal Minutes-hours Usually Almost never
DYSTONIA Daytime Hours Rarely Sometimes
DRUG INDUCED Continual Hours-days Rarely Sometimes
PSYCHOGENIC Paroxysmal Variable Never Sometimes
BRAINSTEM Continual Continual Sometimes Usually

After the medical history is obtained, the first examination of the patient should be TFL. Per oral examination methods, especially when the tongue of the patient is grasped, are almost useless in the diagnosis of PVFM, which is usually diagnosed by laryngoscopy. The diagnosis should be considered when there are findings of: (1) inappropriate vocal fold adduction during inspiration (>50% medialization but less than full closure), (2) paroxysmal inability to abduct the vocal folds (“transient abductor paralysis”), or (3) a combination of these findings. A number of laryngeal findings have been reported in the literature, including a posterior glottal chink during inspiration2 and expiration,6,10 and when symptomatic and asymptomatic.11

There is one group of patients that comprises a notable exception. Patients with LPR-induced paroxysmal LS may have normal phasic vocal fold movement during some examinations. However, these patients have other findings characteristic of LPR (edema, erythema, posterior commissure hypertrophy, and granulation).

During TFL, the patient is asked to: (1) alternatively phonate the vowel /i/ and sniff, in rapid alternating succession, (2) take fast, deep breaths, (3) cough, throat clear, or chuckle, followed by a deep breath, (4) count to fifty, rapidly and loudly, (5) read a written passage in a loud voice, and (6) sing. These maneuvers may reveal a pattern of adduction and abduction consistent with PVFM and a specific diagnosis.

Generally recommended in the work-up of a PVFM patient is pulmonary function testing, particularly to rule out asthma or other lower respiratory diseases. A truncated inspiratory limb of the flow-volume loop is typically observed with PVFM patients, but not with asthma patients.13 Murry et al. also reported a reduced ratio of forced inspiratory volume to forced inspiratory vital capacity for PVFM patients.15 Additional testing may be warranted depending on the suspected cause of PVFM. Such include serial laryngeal examinations by TFL, pH monitoring, neuropsychiatric evaluation, placebo injections, acoustic analysis, audio-recordings of the patient’s breathing during sleep, and radiographic examinations. In selected cases, therapeutic trials of antireflux medication or laryngeal injections of Botox may be indicated.

For reflux-induced PVFM, a firm diagnosis can be made when positive pH monitoring data are combined with the medical history and laryngeal findings of LPR. In addition, resolution of symptoms with a therapeutic trial of aggressive antireflux therapy may confirm the diagnosis.

The medical history can give important clues for patients suspected of having respiratory-type laryngeal dystonia. Unlike patients in the other PVFM groups, patients with respiratory-type laryngeal dystonia describe a progressive onset of the PVFM over a period weeks, months, or years. In addition, such patients usually deny having other symptoms. On occasion, differentiating dystonic from psychogenic PVFM can be a difficult task.

Except for patients in the brainstem abnormality group (who often require tracheotomy), patients with PVFM usually do not have respiratory obstruction severe enough to warrant emergency airway intervention. Of the other groups of patients with PVFM, dystonia patients appear next in terms of the frequency of need for airway support, followed by the psychogenic group, the asthma group, and the LPR group.

Regardless of the underlying cause, on the very first visit, PVFM patients require counseling and training (breathing recovery exercises) by a speech-language pathologist.15,17 We use the quick-sniff-slow-blow technique because it usually aborts PVFM and LS attacks. This type of intervention provides reassurance for fearful patients, and initiates the therapy program (that includes additional counseling, respiratory exercises that focus on exhalation and rhythmic abdominal movement patterns, and, in some cases, resonant voice and easy-onset voice exercises). The variety of techniques and duration of therapy is individualized according to the underlying cause of PVFM as well as the needs and responsiveness of each individual patient.

SUMMARY

PVFM presents the clinician with an interesting differential diagnosis. The causes of PVFM, in order of frequency of occurrence are: (1) laryngopharyngeal reflux (LPR), (2) respiratory-type laryngeal dystonia, (3) abnormalities of the brainstem, (4) brain injuries such as stroke and closed head injuries, and (5) psychogenic stridor. The work-up of PVFM requires a multidisciplinary approach and a variety of diagnostic methods. Likewise, treatment must be individualized.

REFERENCES
1. Ward PH, Hanson DG, Berci G. Observations on central neurologic etiology for laryngeal dysfunction. Ann Otol Rhinol Laryngol 1981;90:430-441.
2. Christopher KL, Wood RP, Eckert RC, Blager FB, et al. Vocal-cord dysfunction presenting as asthma. NEJM 1983;308:1566-70.
3. Patterson R, Schatz M, Horton M. Munchausen’s stridor: non-organic laryngeal obstruction. Clin Allergy 1974;4:307-310.
4. Appleblatt KL, Baker SR. Functional airway obstruction. A new syndrome. Arch Otolaryngol 1981;107:305-307.
5. Kellman RM, Leopold DA. Paradoxical vocal fold motion: an important cause of stridor. Laryngoscope 1982;92:58-60.
6. Martin RJ, Blager FB, Gay ML, et al. Paradoxical vocal cord motion in presumed asthmatics. Semin Respir Crit Care Med 1987;8:332-8.
7. George MK, O’Connell JE, Batch AJ. Paradoxical vocal fold motion: an unusual cause of stridor. J Laryngol Otol 1991;105:312-314.
8. Koufman, JA. Paradoxical vocal cord movement. The Visible Voice 1994;3:49-53 & 70-71.
9. Maschka DA, Bauman NM, McCray PB, Jr., Hoffman HT, et al. A classification scheme for paradoxical vocal cord motion. Laryngoscope 1997;107:1429-1435.
10. Brugman SM, Simons SM. Vocal cord dysfunction: Don’t mistake it for asthma. The Physician and Sports Medicine 1998;26:63-74.
11. Treole K, Trudeau MD, Forrest LA. Endoscopic and stroboscopic description of adults with paradoxical vocal fold dysfunction. J Voice 1999;13:143-52.
12. Andrianopoulos MV, Gallivan GJ, Gallivan KH. PVCM, PVCD, EPL, and irritable larynx syndrome: what are we talking about and how do we treat it? J Voice 2000;14:607-18.
13. Mathers-Schmidt BA. Paradoxical vocal fold motion: a tutorial on a complex disorder and the speech-language pathologist’s role. Am J Speech Lang Path 2001;10:111-25.
14. Altman KW, Simpson CB, Amin MR, et al. Cough and paradoxical vocal fold motion. Otolaryngol Head Neck Surg 2002;127:501-511.
15. Murry T, Tabaee A, Aviv J. Respiratory retraining of refractory cough and laryngopharyngeal reflux in patients with paradoxical vocal fold movement disorder. Laryngoscope 2004;114:1341-44.
16. Patel NJ, Jorgensen C, Kuhn J, Merati AL. Concurrent laryngeal abnormalities in patients with paradoxical vocal fold dysfunction. Otolaryngol Head Neck Surg 2004;130:686-689.
17. Murry T, Tabaee A, Owczarzak V, Aviv J. Respiratory retraining therapy and management of laryngopharyngeal reflux in the treatment of patients with cough and paradoxical vocal fold movement. Ann Otol Rhinol Laryngol 2006;115:754-58.
18. Loughlin CJ, Koufman JA. Paroxysmal laryngospasm secondary to gastroesophageal reflux. Laryngoscope 1996;106:1502-1505.
19. Henderson PS, Cohen JI, Jarnberg P-E, et al. A canine model for studying laryngospasm and its prevention. Laryngoscope 1992;102:1237-41.
20. Bauman NM, Sandler AD, Schmidt C, et al. Reflex laryngospasm induced by stimulation of distal afferents. Laryngoscope 1994;104:209-14.
21. Loughlin CJ, Koufman JA, Averill DB, et al. Acid-induced laryngospasm in a canine model. Laryngoscope 1996;106:1506-1509.
22. Duke SG, Postma GN, McGuirt Jr. WF, et al. Laryngospasm and diaphragmatic arrest in the immature canine after laryngeal acid exposure: a possible model for sudden infant death syndrome (SIDS). Ann Otol Rhinol Laryngol 2001;110:729-733.
23. Koufman JA. (Unpublished data 2005).
24. Collett PW, Brancatisano T, Konno K. Changes in glottic aperture during bronchial asthma. Am Rev Respir Dis 1983;128:719-723.
25. Harding SM, Richter JE. The role of gastroesophageal reflux in chronic cough and asthma. Chest 1997;111:1389-1402.
26. Koufman JA. The otolaryngologic manifestations of gastroesophageal reflux disease (GERD): A clinical investigation of 225 patients using ambulatory 24-hour pH monitoring and an experimental investigation of the role of acid and pepsin in the development of laryngeal injury. Laryngoscope 1991;101 (Suppl. 53):1-78.
27. Little JP, Matthews BL, Glock MS, et al. Extraesophageal pediatric reflux: 24-hour double-probe pH monitoring of 222 children. Ann Otol Rhinol Laryngol Suppl 1997;169:1-16.
28. Belafsky PC, Postma GN, Koufman JA. The validity and reliability of the reflux finding score (RFS). Laryngoscope 2001;111:1313-1317.
29. Koufman JA, Aviv JE, Casiano RR, Shaw GY. Position statement of the American Academy of Otolaryngology-Head and Neck Surgery on laryngopharyngeal reflux. Otolaryngol Head Neck Surg 2002;127:32-35.
30. Belafsky PC, Postma GN, Koufman JA. Validity and reliability of the reflux symptom index (RSI). J Voice 2002;16:274-77.
31. Carrau RL, Khidr A, Gold KF, et al. Validation of a quality-of-life instrument for laryngopharyngeal reflux. Arch Otolaryngol Head Neck Surg 2005;131:315-20.
32. Amin MR, Postma GN, Johnson P, et al. Proton pump inhibitor resistance in the treatment of laryngopharyngeal reflux. Otolaryngol Head Neck Surg 2001;125:374-378.
33. Westcott CJ, Hopkins MB, Bach KK, et al. Fundoplication for laryngopharyngeal reflux. J Amer Coll Surg 2004;199:23-30.
34. Blitzer A, Brin MF. Laryngeal dystonia: a series with botulinum toxin therapy. Ann Otol Rhinol Laryngol 1991;100:85-89.
35. Koek RJ, Pi EH. Acute laryngeal dystonic reactions to neuroleptics. Psychosomatics 1989;30:359-364.
36. Stoelting RK. Pharmacology and Physiology in Anesthetic Practice. page 112, Philadelphia, J. B. Lippincott Co., 1987.
37. Holinger PC, Holinger LD, Reichert TJ, Holinger PH. Respiratory obstruction and apnea in infants with bilateral abductor vocal fold paralysis, meningomyelocele, hydrocephalus, and Arnold-Chiari malformation. J Pediatrics 1978;92:368-373.
38. Charney EB, Rorke LB, Sutton LN, Schut L. Management of Chiari II complications in infants with meningomyelocele. J Pediatrics 1987;111:364-371.
39. Snyder HS, Weiss E: Hysterical stridor: a benign cause of upper airway obstruction. Ann Emer Med 1989;18:991-994.
40. Walker FO, Koufman JA. Induction of psychogenic respiratory distress. (Unpublished data).