Impact of obstructive sleep apnea syndrome on peripheral nerves and the effect of continuous positive airway pressure: a prospective observational case series

Introduction
Obstructive sleep apnea syndrome (OSAS) is suggested to have a strong association with peripheral neuropathy (PNP). However, knowledge about this relationship is still very limited. The aim of this prospective case series was to investigate the peripheral nerves in OSAS patients, along with related clinical symptoms, and to assess the effect of continuous positive airway pressure (CPAP) therapy.

Material and methods
The nerves of upper and lower extremities of 25 patients with moderate to severe OSAS who complained of symptoms suggestive of peripheral neuropathy (PNP) were investigated electrophysiologically. The cross-sectional area (CSA) of the median nerve at the wrist and of the ulnar nerve in the epicondylar groove were assessed with ultrasound. Fifteen patients who showed abnormalities were then reassessed after 3 months of CPAP therapy, and again after an additional 6 months.

Results
The most common findings were carpal tunnel syndrome (CTS) and ulnar neuropathy at the elbow (UNE). Surprisingly, CTS was seen in ultrasound twice as frequently as in electrophysiology. The main symptom was numbness in the upper and lower extremities. CPAP therapy reduced the CSA, improved the conduction at entrapment sites and alleviated the symptoms in some of the patients.

Conclusions
CTS and UNE are the most frequent neuropathies in patients with OSAS. However, the clinical symptoms tend to be more generalized. CPAP therapy seems to be beneficial for both objective measurements and subjective symptoms.