Surface-Evoked Laryngeal Sensory Action Potential Evaluation in Neurogenic Chronic Cough *Jonathan M. Bock, *Ian J. Koszewski, *Joel H. Blumin, *Robert J. Toohill, *,†Albert L. Merati, ‡Thomas E. Prieto, and ‡,§Safwan S. Jaradeh, *zMilwaukee, Wisconsin, ySeattle, Washington, and xPalo Alto, California Summary: Objectives. Neurogenic chronic cough is currently a diagnosis of exclusion. We hypothesized that surface-evoked laryngeal sensory action potential (SELSAP) testing could be used to help establish a diagnosis of laryn- geal sensory neuropathy as a cause of chronic cough, based on altered SELSAP waveform morphology. Study Design. Retrospective cohort study. Methods. Laryngeal electromyographic (EMG) data including SELSAP waveform testing from patients with chronic cough were directly compared with a control population without significant laryngeal symptoms, and statistical analysis of unilateral and bilateral neuropathy injury subgroups was performed. Results. Thirty patients with a chief complaint of chronic cough underwent laryngeal EMG testing since January 2000 with needle EMG and surface nerve conduction studies. SELSAP waveform analysis of unilateral and bilateral laryn- geal neuropathy demonstrated significantly lowered median SELSAP peak amplitude compared with controls (P < 0.01). Conclusions. Patients with suspected neurogenic chronic cough demonstrate statistically significant alterations in SELSAP waveform that can support a diagnosis of laryngeal sensory neuropathy. Key Words: Laryngeal EMG–Chronic cough–SELSAP–Neuropathy–Evoked potential–Neurogenic. INTRODUCTION Patients with chronic cough present a diagnostic and therapeu- tic challenge to the otolaryngologist. 1 Chronic cough is defined as a cough with a duration of greater than 8 weeks, and it is one of the most common reasons for specialist referral in current medical practice. 2,3 Chronic cough can be induced by a wide variety of causes affecting multiple different physiological and sensory pathways including upper airway cough syndrome, cough-variant asthma, gastroesophageal reflux dis- ease (GERD), or laryngopharyngeal reflux. 2,4 Published guidelines exist that delineate possible approaches for the management of these challenging patients. 2,3,5 Proper diagnosis is crucial in developing an effective treatment protocol for chronic cough. 6 Studies have shown that up to 42% of patients with chronic cough will not improve despite extensive workup and directed therapy. 1 These patients often undergo frequent radiologic examinations, receive numerous pharmacologic interventions, and endure multiple specialist referrals without successful diagnosis and treatment of their cough. 7 Treatment failure for patients with chronic cough is associated with a significantly impaired health-related quality of life, 8 and many of these patients suffer from chest wall pain, stress-related urine incontinence, sore throat, dysphonia, and social embarrassment. It also has an adverse impact on their family and partners. 1 It is therefore imperative that better directed therapies and testing for various cough etiologies be developed. Neurogenic chronic cough (NCC) has emerged as a possible diagnosis for this challenging population. 7,9,10 Cranial neuropathies are known to lead to deranged motor and sensory function in multiple head and neck disease states such as Bell’s palsy, trigeminal neuralgia, and glossopharyngeal neuralgia. 11 Similar involvement of the internal branch of the superior laryn- geal nerve (SLN) may lead to laryngeal sensory neuropathy and subsequent induction of NCC. 10 NCC is typically suspected in patients with chronic cough after multiple common etiologies of cough have been excluded including lack of tobacco use his- tory and a negative chest X-ray. Diagnosis of NCC is supported by a thorough history and careful physical examination. 12 Laryn- geal sensory neuropathy may occur after viral infection, chemi- cal inhalation, or after sources of mechanical trauma to the vagus or SLN. 13 It is often accompanied by motor neuropathy as evi- denced by subtle vocal fold paresis, but determination of altered SLN function on videostroboscopy remains challenging. 14,15 Many patients with NCC will respond to neuromodulatory medications, drawing parallels between chronic cough and other chronic neuropathies such as chronic pain syndromes. 13 Despite increasing evidence of NCC in clinical practice and pub- lished literature, few modalities for diagnosing NCC beyond physical examination exist. 16 NCC continues to be a diagnosis of exclusion, 14 and treatment is empiric. 2,3,5,17 Laryngeal sensory nerve function can be tested using laryn- geal surface-evoked potentials to detect conduction along the internal branch of the SLN, termed surface-evoked laryngeal sensory action potential (SELSAP) testing. 18 The SELSAP technique involves transcutaneous stimulation of the SLN through noninvasive surface cathodes placed adjacent to the mastoid prominence, with evoked potential measurement Accepted for publication February 20, 2014. This work was performed at the Medical College of Wisconsin, Milwaukee, Wisconsin. Financial disclosures: None for all listed authors. There was no funding for this work. Conflicts of interest: None. Presented at the 2012 Annual Meeting of the American Laryngological Association at Combined Otolaryngology Spring Meeting (COSM), San Diego, California, on April 18, 2012. From the *Department of Otolaryngology & Communication Sciences, Medical Col- lege of Wisconsin, Milwaukee, Wisconsin; yDepartment of Otolaryngology—Head and Neck Surgery, University of Washington, Seattle, Washington; zDepartment of Neurology, Medical College of Wisconsin, Milwaukee, Wisconsin; and the xDepartment of Neurology, Stanford University Medical Center, Palo Alto, California. Address correspondence and reprint requests to Jonathan M. Bock, Department of Otolaryngology & Communication Sciences, 9200 W. Wisconsin Ave, Milwaukee, WI 53226. E-mail: jbock@mcw.edu Journal of Voice, Vol. -, No. -, pp. 1-7 0892-1997/$36.00 Ó 2014 The Voice Foundation http://dx.doi.org/10.1016/j.jvoice.2014.02.009