Patients with AIDS and progressive multifocal leucoencephalopathy (PML) may be missed if they present with atypical symptoms, as shown by a case study. The study is the first to report progressive myoclonic ataxia caused by PML. This exceptional presentation confounded diagnosis because of atypical symptoms and neurological lesions confined for the first few months to the grey matter of the brain. PML typically produces lesions in the white matter. Reports of similar imaging findings in AIDS patients are growing, and the report’s author call for MRI diagnostic criteria for PML to be expanded and for PML to be listed in the differential diagnoses for all patients with HIV, since prospects of improved outcome with new treatments rest with a correct early diagnosis.

The case describes the disease course over 13 months in a 36 year old white man positive for HIV-1 and hepatitis C, taking zidovudine, who presented initially with gait ataxia and intention tremor in his arms, worsening to myoclonic ataxia, then tetraparesis and physical deterioration, followed by death from pneumonia. Imaging throughout showed lesions only in the grey matter of the brain, except in the final months. Pathological examination of the brain and in situ hybridisation for JC virus confirmed PML.

PML is a rare disease in which oligodendrons are destroyed by JC virus, a common infective agent in childhood, which persists in latent form. The virus can be activated by infection with HIV-1, and it may be present in up to 5% of AIDS patients.

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Brain necropsy. (A) Coronal section of the basal ganglia showing demyelinating lesions and cavitation in the right thalamus (Luxol fast blue stain). (B) Demyelinating lesion with reactive astrocytes, macrophages, and oligodendroglial nuclear inclusions (Luxol fast blue stain (x400). In situ hybridisation for JC virus, with positive oligodendroglial nuclei (x300).