Progressive multifocal leucoencephalopathy (PML) in an immunocompetent patient

<h3>Background</h3> PML is very rare and often fatal in immunocompetent hosts. It results from reactivation of the JC virus (JCV). A thorough search for an immunocompromising condition must be undertaken. Treatment options are limited and require multidisciplinary input. <h3>Case Presentation</h3> A previously well 59-year-old man presented with an 8-week history of progressive right-sided hemiparesis, dysphasia, and ataxia. He drank 70 units of alcohol per week. We suspected PML based on typical radiological abnormalities but initial PCR for JCV in CSF was negative. The diagnosis was confirmed on brain biopsy. Extensive serological testing, CT and CT-PET scan of the body were normal. HIV testing was negative, but serum electrophoresis revealed a monoclonal gammopathy of uncertain significance (MGUS). Clinical and radiological deterioration continued, and a short course of intravenous methylprednisolone was given to treat immune reconstitution syndrome (IRIS). He made a gradual clinical and radiological improvement but had significant residual neurological disability at 1-year follow-up. <h3>Conclusion</h3> In our patient excessive alcohol intake may have caused immune dysfunction, but the MGUS was not felt to have contributed. We considered treatment with the immune checkpoint inhibitor pembrolizumab but did not proceed as immune reconstitution and viral clearance appeared to occur spontaneously with sustained improvement thereafter.