Abstract
BACKGROUND: John Cunningham virus (JCV) is known to cause progressive multifocal leukoencephalopathy (PML) in immuno-compromised patients due to lytic infection of oligodendrocytes and astrocytes. Rarely, it may also present as granule cell neuronopathy (GCN), leading to degeneration of cerebellar granule cell neurons. It is described in patients with underlying conditions or medication contributing to immune compromise. Case Presentation. A 73-year-old man presented with ataxia and difficulty in speech which began 3 months after initiation of treatment for idiopathic thrombocytopenic purpura with rituximab. Neurological examination was significant for torsional nystagmus, motor aphasia, right-sided dysmetria, and dysdiadochokinesia with gait ataxia. Magnetic resonance imaging (MRI) showed right cerebellar lesion and cerebrospinal fluid (CSF) polymerase chain reaction (PCR) was positive for JC virus. CONCLUSION: The diagnosis of JC virus-related cerebellar disease can be missed, due to the subacute to chronic onset and challenges in detection. Clinicians should have a high degree of suspicion for development of these symptoms, even a few months after initiation of immune-modulatory therapy because the progression and outcomes can be disastrous.