A case of cerebellar-limited HIV-associated progressive multifocal leukoencephalopathy diagnosed with the aid of the shrimp sign

A 43-year-old man presented with dizziness and slurred speech. A brain MRI with diffusion-weighted imaging and fluid-attenuated inversion recovery imaging revealed an abnormally high signal in the white matter of the left cerebellar hemisphere sparing the dentate nucleus, consistent with the characteristic "shrimp sign". Pathological findings from brain biopsy were non-specific, however, JC virus-DNA was detected in the cerebrospinal fluid and anti-human immunodeficiency virus (HIV) antibodies were positive in the serum, leading to a diagnosis of HIV-associated progressive multifocal leukoencephalopathy (PML) limited to the cerebellum. Antiretroviral therapy was initiated, resulting in a favorable clinical course. The shrimp sign is highly specific to cerebellar PML and may facilitate an early diagnosis.