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Denver, CO
Dr. Christopher is Associate Clinical Professor of Medicine, University of Colorado Health Sciences Center.
Correspondence to: Kent L. Christopher, MD, FCCP, 9086 East Colorado Circle, Denver, CO 80231; e-mail:drkchristopher{at}comcast.net
In this issue of CHEST (see page 905), Mikita and Parker1 demonstrate that ambulatory vocal cord dysfunction (VCD) patients, who likely had an underlying somatoform disorder, had significantly more physician visits and subspecialty visits (particularly pulmonary) during the year prior to their VCD diagnosis than matched control subjects with moderate persistent asthma, which is the disorder that VCD often mimics.
The VCD diagnostic approach of Mikita and Parker1 is impressive from two perspectives. Because of their role in determining soldier fitness for duty, they implemented an aggressive evaluation for unexplained dyspnea, typically including a comprehensive assessment for bronchial hyperreactivity. Consequently, they were able to exclude concomitant asthma in 84% of their 25 VCD patients. Ironically, the identified VCD patients were largely retirees and dependents rather than active duty military.
Second, the authors state that they followed the standardized laryngoscopic procedure and diagnostic criteria for VCD.2 These criteria evolved from the endoscopic findings that we described in 19833 in the first report of VCD presenting as asthma. To summarize, when laryngoscopy is performed utilizing adequate topical anesthesia in symptomatic patients, the presence of inspiratory or inspiratory and expiratory vocal cord adduction with a posterior glottic chink confirms the diagnosis of VCD. The findings are illustrated in Figure 1 .
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The first answers are obvious: (1) it is a relatively uncommon condition; (2) the disorder closely mimics asthma; (3) intermittent symptoms make endoscopic confirmation logistically difficult; and (4) by the very nature of a somatoform disorder, diagnosis of the condition is elusive. Another problem is that the definition of the term VCD has also become elusive. We originally selected the term VCD to identify a very specific clinical syndrome that had defined endoscopic features and mimicked asthma.3 Over time, VCD has become a very loosely applied descriptor for inspiratory or isolated expiratory vocal cord adduction, either with or without the presence of the posterior chink. Furthermore, the term VCD has been applied to an ever-expanding array of clinical presentations. There are a number of additional diseases or disorders that are manifested by abnormal vocal cord motion during breathing. They likely have different medical or psychological etiologies and constitute a spectrum of clinical presentations with varying severity. Confusion will continue if a spectrum of disorders is collectively lumped together as VCD.
Clarity is further obscured if what has been loosely identified as VCD limited to the expiratory phase may not be dysfunctional at all. Adduction of the vocal cords at the end of exhalation is normal.2 Higenbottam4 demonstrated that adduction of the vocal cords occurred in early exhalation when healthy volunteers underwent histamine bronchoprovocation. Though expiratory vocal cord adduction in patients with obstructive lung disease may be pathophysiologic under certain conditions, we should not jump to conclusions. Higenbottam5 showed that patients with airway obstruction had early expiratory adduction of the vocal cords. The most marked expiratory adduction occurred with the lowest FEV1 values. Collett and coworkers6 showed that vocal cord adduction occurs during mid-exhalation in asthmatic patients with experimentally induced bronchoconstriction. The key insight is that the reversal of the glottic obstruction occurred with continuous positive airway pressure. This finding suggests that expiratory adduction in asthma patients may contribute to hyperinflation, allowing a beneficial reduction in persistent inspiratory muscle activity during exhalation.
Confusion persists regarding the potential coexistence of asthma in patients with a somatoform disorder that meets the laryngoscopic criteria for VCD. In these patients, glottic obstruction often occurs on expiration as well as on inspiration. Therefore, expiratory flow may be limited on spirometry and may mimic asthma. Figure 1 in the original description of this disorder3 shows obstruction of the expiratory flow-volume relationship in addition to inspiratory flow limitation in patient 5. The study was performed while the patient was symptomatic, and the results could be interpreted as VCD with concomitant asthma. However, subsequent bronchoprovocation studies excluded asthma. The pitfalls of diagnosing concomitant asthma based on an expiratory obstructive pattern on spirometry and bronchoprovocation studies have been recognized.2789 Noninvasive, practical, reliable, appropriately sensitive, specific, and easily interpreted tools that allow partitioning of the resistances in the upper and lower airways are needed to further our understanding of the physiologic and pathophysiologic roles of the larynx in lung disease.
The message is clear. We need to move away from using the term VCD as a catch-all descriptor for vocal cord adduction during breathing. A greater understanding of physiologic vs pathophysiologic alterations in the glottic aperture is required. Future prospective studies must objectively, meticulously, and precisely define other diseases and disorders affecting the glottis during breathing. We need to become "splitters" rather than "lumpers." Physiologic and anatomic correlations are key.
Though the prevalence of VCD is low, Mikita and Parker1 have confirmed a significant negative impact on health-care utilization. The plethora of case reports are testimony to impaired quality of life. It is high time to conduct appropriate scientific inquiries, including prospective, comprehensive multicenter trials at institutions with the commitment and resources that are necessary to maximize our understanding of conditions that have been collectively lumped together under the term VCD.
Footnotes
Dr. Christopher has no conflict of interest to disclose.
References
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