Cerebellar progressive multifocal leucoencephalopathy identified by the shrimp sign

Area of Science:

• Neurology
• Virology
• Immunology

Background:

• Progressive multifocal leucoencephalopathy (PML) is a rare demyelinating disease caused by the John Cunningham (JC) virus.
• JC virus reactivation is typically associated with immunosuppressive states like AIDS, immunomodulatory therapy, or hematological malignancies.
• PML commonly affects periventricular and juxtacortical white matter, with isolated cerebellar or brainstem involvement being rare.

Observation:

• A case study of a man in his 70s presenting with rapidly progressive cerebellar ataxia, ptosis, and bipyramidal signs.
• Initial investigations ruled out other causes such as viral cerebellar infections, ADEM, paraneoplastic cerebellar degeneration, or structural lesions.
• MRI PET revealed a characteristic "shrimp sign," suggesting cerebellar PML.

Findings:

• Cerebrospinal fluid (CSF) analysis confirmed PML through positive JC virus PCR.
• The patient had no known immunocompromised state, but was found to have idiopathic CD4 lymphopenia.
• This case demonstrates cerebellar PML in an individual without overt immunosuppression.

Implications:

• The "shrimp sign" on MRI is a crucial diagnostic indicator for cerebellar PML.
• PML should be considered in the differential diagnosis even in immunocompetent individuals presenting with relevant neurological symptoms.
• Idiopathic CD4 lymphopenia can be an underlying factor in PML development, emphasizing the need for thorough immune workup.