Isolated small-vessel angiitis of the central nervous system.

Isolated cerebral angiitis was confirmed by brain parenchyma biopsy in a 31-year-old man with a rapidly progressive encephalopathy and normal cerebral angiography and magnetic resonance imaging. Presenting features of aphasia, hemiparesis, and lethargy resembled herpes simplex encephalitis. Severe neurologic deficits rapidly resolved with steroids plus cyclophosphamide, and he remains in remission after two years. This case illustrates potentially misleading early manifestations of isolated cerebral angiitis, diagnostic limitations of angiography, the value of biopsy that includes both brain parenchyma and leptomeninges, and the potential efficacy of steroid and cyclophosphamide therapy in small-vessel disease. Clinical features and response to treatment vary widely in reported cases, suggesting that isolated cerebral angiitis may have diverse etiologies.