Unexplained cough may have its origins in the brain stem

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Unexplained chronic cough may be caused by compression of nerves at the brain stem

Laryngeal symptoms like chronic cough and swallowing problems may be caused by pressure on cranial nerves 9 and 10 at the brainstem.

A team of researchers from MUSC (The Medical University of South Carolina) led by Lucinda Halstead, M.D., associate professor of medicine in MUSC’s Department of Otolaryngology: Head & Neck Surgery and medical director of the Evelyn Trammell Institute for Voice and Swallowing have shown that relieving the compression of cranial nerves 9 and 10 at the brainstem can improve such patients.

Although sudden coughing episode is a protective reflex to clear the airways, chronic cough can be very disturbing. Cough is just one of several laryngeal symptoms including hoarseness and dysphoric breathing that can become debilitating. When a patient presents with chronic laryngeal symptoms (persisting for more than eight weeks and not improving with standard treatment), physicians follow a step-by-step approach to look at the most common causes. More than 86% of chronic coughs which do not improve with medical treatment are caused by post-nasal drainage, asthma or gastroesophageal reflux disease.

“Our study shows that when we can’t identify a cause for vocal fold weakness based on the standard work up, the next step may be to look at the brain stem”

However, the cause of these severe laryngeal symptoms can not be identified in many patients, and the only treatment is to manage them with medication and rehabilitation therapy.

If a full history and exam do not identify the cause, an ENT specialist (otolaryngologist) evaluates the larynx. In some patients, this turns up asymmetrical movement of the vocal fold (the vocal cords) or vocal fold paralysis. The cause is usually a lesion or another structure pressing on one of the nerves that activates the vocal fold and swallowing (cranial nerves nine and ten). If the usual CT or MRI scans don’t show anything then a viral origin is suspected or etiology is described as unknown.

The team identified 149 candidates and, after extensive work-ups to eliminate all other causes, they found that 33% (49/149) had nerve compression at the brainstem. Their symptoms included dysphonia (51%), chronic cough (39%), dysphoric breathing (6%) and dysphagia (4%). About half of them underwent surgical decompression and another half elected non-surgical/standard-of-care treatment.

Results showed that 42% of the surgical group reported near-complete or complete symptom resolution compared to 8% in the non-surgical group and none of the non-surgical patients demonstrated improved laryngeal exam findings, while 43% of surgical patients demonstrated improvements and 29% demonstrated resolution of their laryngeal exam findings.

“Our study shows that when we can’t identify a cause for vocal fold weakness based on the standard work up, the next step may be to look at the brain stem,” Halstead said. “It’s so important that we now have one more thing to look at and one more thing we can offer as definitive treatment.”