Alpha-coma: clinical and evoked potential studies.
Simultaneous brainstem auditory and somatosensory evoked potential studies to median nerve stimulation were performed in two comatose patients, having diffuse alpha-pattern in their EEGs. CT scan of the brain in both cases did not reveal any mass lesion. In Case 1, the clinical and evoked potential studies suggested a brain stem lesion, and in Case 2 there was diffuse encephalopathy, with asymmetric dysfunction of the brainstem as seen in the evoked potential patterns. The suggested separation of alpha-pattern into two distinct groups, based on the reactivity and the presence or absence of sleep activities, into brainstem and diffuse cortical lesions could not be supported by our evoked potential studies. Our study, based on the observations of the evoked potential studies, indicated that the reactivity to sensory stimulation and intermittent attenuation of diffuse alpha-like activity relate to the integrity of the ascending sensory inputs to the thalamus. In the absence of evoked potential data, the localization of lesion(s) in alpha-coma pattern may be imprecise. Moreover, the circadian sleep rhythms and the presence or absence of "sleep spindles" appeared to depend on the inputs of the ascending sensory pathways to the structures generating the sleep activities. The specific neuronal structures generating the alpha-pattern still remain unidentified; however, this pattern seems to be originating from the structures rostral to the mesencephalon, possibly in the thalamic-thalamocortical circuits.
D000328:Adult; D000513:Alpha Rhythm; D003128:Coma / Q000503:physiopathology*; D005072:Evoked Potentials, Auditory; D005073:Evoked Potentials, Somatosensory; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D012890:Sleep / Q000502:physiology