Acute encephalopathy: diagnosis and outcome in patients at a regional neurological unit

Sixty-five patients with a diagnosis of acute encephalitis or encephalopathy were discharged from a regional neurological unit over a 17-year period. Investigation during the acute illness, or subsequent clinical and laboratory observations, yielded a definite or probable diagnosis in 34 of these patients, including herpes simplex encephalitis (8 cases), encephalitis due to other identified viruses (7 cases), vascular disease (7 cases) and multiple sclerosis (4 cases). In these 34 patients, mortality relating to the presenting illness was 50% and a further 29% had significant long-term neurological morbidity. In the other 31 patients, no cause for the encephalopathy was identified, despite extensive investigation. These patients had an alteration in conscious state, often with recurrent seizures (45%), focal neurological signs (52%), pyrexia (65%), abnormal electroencephalogram (85%) and cerebrospinal fluid lymphocytosis (80%). During follow-up (6 months to 15 years) none had recurrent encephalopathy, and 65% eventually made a complete recovery, although delayed by seizures in 6% and psychiatric illness in 13%. The mortality in this group relating to the acute illness was 6%. Overall, nearly half the patients with a discharge diagnosis of acute encephalitis or encephalopathy had a good prognosis for recovery, following a monophasic illness of undetermined cause.