JC virus granular neuronopathy and rhombencephalic progressive multifocal leukoencephalopathy: case report and review of the literature.

JC virus (JCV) granular neuronopathy remains an under-appreciated phenomenon whereby JCV inhabits neurons in the granular layer of the cerebellum causing neuronal loss, gliosis and a clinical cerebellar syndrome. The following case describes a man with sarcoidosis and idiopathic leukopenia who developed a clinical cerebellar syndrome due to JCV granular neuronopathy, followed by neurological decline due to rhombencephalic progressive multifocal leukoencephalopathy. This case reminds us of the ability of JCV to produce dual neuropathology which includes JCV granular neuronopathy, and the pathogenesis and clinical implications for this phenomenon are discussed.