Progressive Multifocal Leukoencephalopathy in a Kidney Transplant Recipient.

Progressive multifocal leukoencephalopathy (PML) is a debilitating and often fatal viral disease of the central nervous system. A 39-year-old male kidney transplant recipient presented to our hospital with weakness of the left arm and leg, his immunosuppressive regimen consisted of tacrolimus, mycophenolate sodium, and meprednisone. Magnetic resonance imaging of the brain revealed hypercellularity in neural tissue and a lesion affecting the right ventral and lateral areas of the thalamus and the posterior limb of the internal capsule. The cerebrospinal fluid tested negative for bacteria, fungi, and acid-fast bacilli; cytology revealed no malignant cells. The clinical presentation, brain imaging, biopsy results showing a demyelinating process, and absence of atypical proliferation all suggested that the first diagnosis to be ruled out was PML. The weakness resolved after withdrawal of tacrolimus and mycophenolate sodium. On day 250 after presentation, no further neurologic deterioration was evident, and renal function was stable. The diagnosis of PML may not always be straightforward. Polymerase chain reaction for detecting John Cunningham virus was not available at our center or in the region. However, a negative result using polymerase chain reaction does not rule out PML.