Hyperviscosity as a possible cause of positive acoustic evoked potential findings in patients with sleep apnea: a dual electrophysiological and hemorheological study.

OBJECTIVE To test the hypothesis that blood hyperviscosity could account for the controversial results observed during electrophysiological evaluation of the brain stem in sleep apnea syndrome. METHODS This was a prospective study of a sample of patients with sleep apnea who were participating in a stroke prevention evaluation. Participants were 610 male patients with obstructive sleep apnea, aged 30-55 years, without large vessel disease on Magnetic Resonance Angiography and neck Doppler sonography, and an infratentorial lesion on head magnetic resonance imaging. Brainstem auditory-evoked potential and hemorheological investigations were carried out. RESULTS Forty-six percent (N=282) of the patients evidenced hyperviscosity and 53% (N=328) had normal rheological findings. Evoked potential changes appeared only in the hyperviscosity positive subgroup. Of these, 84% (N=239) evidenced BAEP changes with 24% (N=57) demonstrating sensorineuronal and 76% (N=182) demonstrating brain stem type abnormalities. After six months of CPAP therapy, hyperviscosity was normalized in 66% (N=159) of patients. BAEP wave III latency values were normalized in 70% (N=112) of these patients. CONCLUSIONS Viscosity changes play an important role in the brainstem electrophysiological abnormalities in apnea patients. These abnormalities can be normalized after six months of CPAP therapy.