Brainstem auditory evoked responses and alpha-pattern coma

Etiology, neurologic correlations, and prognosis in alpha coma

OBJECTIVE

To determine the factors affecting prognosis in alpha coma (AC).

METHODS

Retrospective review of 36 study patients, 36 control coma patients matched for age and etiology, and meta-analysis of 335 cases in the world literature.

RESULTS

Principal causes were cardiorespiratory arrest (CRA) (21 patients); infection, metabolic dysfunction, head trauma (3 each); and drugs, stroke and hypoxia (2 each). Outcome was predicated by EEG reactivity to noxious stimuli. Fourteen of the 15 patients with reactive EEGs, had measurable outcome, 8 awoke - all but two had etiologies other than CRA. Fourteen of 19 patients without EEG reactivity died; two had support discontinued and 3 awoke. Following CRA, 16/21 patients died and 3 had support discontinued. Only 3 patients made a good recovery - all with toxic or metabolic etiologies. Literature meta-analysis of 335 cases showed that overall, AC carried a poor prognosis (76% died). CRA (226 cases) had an 88% mortality; strokes (29 cases), a 90% mortality; hypoxia without cardiac arrest (28 cases), a 61% mortality; drug-induced AC (25 cases), an 8% mortality.

CONCLUSIONS

Although the cause of AC largely predicts outcome, EEG reactivity in AC predicted survival: most patients with reactivity awoke; most of those without, died. Few survivors had meaningful recovery.

[Persistent alpha-vegetative state]

After briefly reviewing the concepts of "coma" and "alpha-coma", we report the case of a patient with presumable Pick's disease who spent several weeks in a vegetative state with a normal and reactive EEG in the alpha range in the later stages of her illness. We (a) emphasize some implications of the appearance of the eyes in such patients, b) stress the importance of distinguishing alpha activity from true alpha rhythm and (c) suggest the category "alpha-coma" should include only those individuals bearing evidence of disorders of the junctional tegmentum of the pons and midbrain. In a complementary way, we propose that patients in a persistent vegetative state displaying normal EEG should be separately classified as persistent "alpha-vegetative state".