[Acoustic evoked potentials (AEP) in obstructive sleep apnea syndrome]

Patients with obstructive sleep apnea syndrome (OSAS) present upper airway obstruction during sleep which can be documented by electromyography. The cause of weakness in oropharyngeal muscles is still unknown. Lesions of pons and medulla oblongata have to be expected. Brainstem auditory evoked potentials (BAEP) may indicate pathological changes in these regions. Several studies described normal BAEP in OSAS-patients. Moderate forms of OSAS as well as central sleep apnea syndromes were investigated, however. In our study 20 patients (17 men, 3 women, mean age 53.9 +/- 2.1 ys) with severe OSAS (apnea/hypopnea-index: 34.2 +/- 14.1/h, part of O2-saturation < or = 90% during sleep (SaO2 < or = 90%): 13.5 +/- 4.2%, minimal nocturnal O2-saturation: 78.0 +/- 2.5%) before starting nCPAP-therapy were investigated. BAEP were elicited after applying clicks 70 dB above threshold to each ear. Means of single wave latencies as well as interpeak latencies (I-V, I-III, III-V) were delayed significantly compared to normal controls. Main prolongations were seen regarding wave latency I (p < or = 0.001) and-interpeak latency I-V (p < or = 0.001). Prolongation of interpeak latencies (mean +/- 2.5 SD) of one or two sides could be demonstrated in 12 out of 20 patients. Pontomesencephal lesions (9 patients) dominated. There was no connection with respiratory parameters. As against pathological BAEP changes correlated with the duration of the disease. In conclusion pathological BAEP indicating brainstem lesions were seen in 60% of the examined OSAS-patients. Mesencephal lesions dominated, number of lesions increased with duration of disease. Therefore pathological findings have not to be considered as cause but as a result of hypoxemia in OSAS. Pathological BAEP may reveal a higher risk for cerebrovascular stroke. Therefore these patients should be leaded to further cerebrovascular investigation.