[Electrophysiological brain-stem diagnosis in patients with a pronounced obstructive sleep apnea syndrome]

The pathophysiological basis of obstructive sleep apnoea syndrome (OSAS) is a loss of tone of the oropharyngeal muscles during sleep, leading to partial and/or total collapse of the oropharyngeal muscle tube. The normal inspiration-synchronous activation (ISA) of the tongue muscles is diminished or lost in patients with OSAS. Observations of OSAS in patients with ischaemic pontomedullary lesions, syringobulbia (syringomyelia), olivo-ponto-cerebellar atrophy or disseminated encephalopathy have indicated that it is due to impairment of ISA. In this study systematic electrophysiological studies (EPS) were undertaken in patients with severe OSAS, as demonstrated by polysomnography, to determine whether, in addition to the central abnormality of oropharyngeal muscular tone, one can demonstrate an increased incidence of subclinical, functional disorder in the brain stem as well as any pointers to a central localization of abnormalities in OSAS.

19 patients with severe OSAS were examined for the presence of subclinical brain-stem lesions by means of acoustic evoked potentials, blinking reflex, masseter reflex, masseter silent period, electronystagmogram together with vestibular testing and magnetic evoked potentials of the tongue musculature.

Findings were unremarkable in 15 of the 19 patients. EPS gave reproducible evidence of functional left pontine (blink reflex) brain-stem lesions in two of the patients and of bilateral pontomesencephalic (masseter reflex) brain-stem lesions in the other two.

In the absence of systematic abnormalities our findings speak against relevant brain-stem lesions being the cause and/or consequence of OSAS.