Axon and Schwann Cell Degeneration in Nerves of Upper Airway Relates to Pharyngeal Dysfunction in Snorers and Patients With Sleep Apnea

BackgroundThe pathophysiologic mechanism of nocturnal obstruction and swallowing dysfunction commonly occurring in patients with sleep apnea is unclear. The goal of this study was to investigate whether nerve injuries in the upper airways of snorers and patients with sleep apnea are associated with pharyngeal dysfunction and severity of sleep apnea.MethodsTwenty-two patients undergoing palatal surgery due to snoring and sleep apnea were investigated for a swallowing dysfunction by using videoradiography. Twelve healthy nonsnoring subjects were included as control subjects. Tissue samples from the soft palate at the base of the uvula were obtained in all patients and control subjects. Nerves and muscle were analyzed with immunohistochemical and morphologic methods, and the findings were correlated with swallowing function and degree of sleep apnea.ResultsIn the soft palate of patients, nerve fascicles exhibited a significantly lower density of axons (5.4 vs 17.9 × 10–3 axons/μm2; P = .02), a smaller percentage area occupied by Schwann cells (17.5% vs 45.2%; P = .001) and a larger number of circular shaped Schwann cells lacking central axons (43.0% vs 12.7%; P < 0.001) compared with control subjects. The low density of axons was significantly related to degree of swallowing dysfunction (r = 0.5; P = .03) and apnea-hypopnea index > 5 (P = .03). Regenerating axons were frequently observed in patients compared with control subjects (11.3 ± 4.2% vs 4.8 ± 2.4%; P = .02).ConclusionsAxon degeneration in preterminal nerves of the soft palate is associated with pharyngeal dysfunction in snorers and patients with sleep apnea. The most likely cause for the nerve injuries is traumatic snoring vibrations and tissue stretch, leading to swallowing dysfunction and increased risk for upper airway obstruction during sleep. The pathophysiologic mechanism of nocturnal obstruction and swallowing dysfunction commonly occurring in patients with sleep apnea is unclear. The goal of this study was to investigate whether nerve injuries in the upper airways of snorers and patients with sleep apnea are associated with pharyngeal dysfunction and severity of sleep apnea. Twenty-two patients undergoing palatal surgery due to snoring and sleep apnea were investigated for a swallowing dysfunction by using videoradiography. Twelve healthy nonsnoring subjects were included as control subjects. Tissue samples from the soft palate at the base of the uvula were obtained in all patients and control subjects. Nerves and muscle were analyzed with immunohistochemical and morphologic methods, and the findings were correlated with swallowing function and degree of sleep apnea. In the soft palate of patients, nerve fascicles exhibited a significantly lower density of axons (5.4 vs 17.9 × 10–3 axons/μm2; P = .02), a smaller percentage area occupied by Schwann cells (17.5% vs 45.2%; P = .001) and a larger number of circular shaped Schwann cells lacking central axons (43.0% vs 12.7%; P < 0.001) compared with control subjects. The low density of axons was significantly related to degree of swallowing dysfunction (r = 0.5; P = .03) and apnea-hypopnea index > 5 (P = .03). Regenerating axons were frequently observed in patients compared with control subjects (11.3 ± 4.2% vs 4.8 ± 2.4%; P = .02). Axon degeneration in preterminal nerves of the soft palate is associated with pharyngeal dysfunction in snorers and patients with sleep apnea. The most likely cause for the nerve injuries is traumatic snoring vibrations and tissue stretch, leading to swallowing dysfunction and increased risk for upper airway obstruction during sleep.