To highlight the radiographic features of infratentorial PML in a patient with Short Telomere Syndrome (STS), a rare genetic condition that predisposes to opportunistic infections.

JCV infection typically causes progressive multifocal leukoencephalopathy (PML) due to viral tropism for glial cells and subsequent damage to white matter. While usually supratentorial, PML can be isolated to the infratentorium or in rare cases, cause selective pontocerebellar damage in a condition known as granule cell neuronopathy (GCN). While these phenotypes are commonly seen in those with HIV-AIDS and iatrogenic immunosuppression, genetic immunodeficiency remains an important consideration. Accordingly, we highlight a case of Short Telomere Syndrome causing infratentorial PML.

Short telomere syndrome presents with widespread symptoms, including immunodeficiency, aplastic anemia, skin hypopigmentation, premature graying and avascular necrosis, all of which were present in our patient. The association between this clinical syndrome and JCV stems from the ability of short telomeres to reduce the absolute quantity and function of T-cell subpopulations. In our patient, this T-cell dysfunction resulted in a case of infratentorial PML, which presented with the pathognomonic “shrimp sign” on MRI.