Abstract

A 74 year–old woman presented in December 2011 with left sided cerebellar symptoms. She was initially diagnosed as having a posterior circulation infarction and discharged from hospital on appropriate medication. However, over the following month she continued to deteriorate, developing increasing unsteadiness, falls, nausea and vomiting. Following a second admission in January 2012 she had a single seizure and developed focal left sided myoclonus affecting mainly the upper limb. Over the following month the myoclonus spread to affect all four limbs, although it remained more prominent on the left side. There was evidence of pathological emotional lability, but no frontal disinhibition. She had no past medical history of note, and had been taking only antihypertensives prior to her initial presentation.

MRI brain showed T2 and FLAIR hyperintensities in both cerebellar hemispheres and the middle cerebellar peduncle which did not demonstrate any mass effect. Further lesions situated in the left cerebellopontine angle and anterior to the medulla demonstrated subtle mass effect with some moulding of the anterior aspect of the cervicomedullary junction. None of the lesions restricted on diffusion weighted imaging. Routine tests revealed no abnormalities, including normal lactate, thyroid function and urine organic acids. Serological autoimmune and paraneoplastic antibody screens were negative. HIV and toxoplasma screen were negative, and PCR for CMV/HSV and JCV were negative in the blood. CSF was acellular, with predominantly CSF oligoclonal bands. CSF glucose was 2.8 mmol/L (plasma 6.1). She continued to deteriorate, and was given a trial of intravenous methyprednisolone, which only appeared to accelerate her downward trajectory. She was fully investigated for the presence of an occult malignancy with FDG–PET, which showed non–specific uptake in the thyroid but otherwise no abnormal uptake outside the cerebellar lesions seen on MRI. There was subtle and patchy reduction of tracer uptake involving all cerebral cortices. Thyroid USS revealed a multi–nodular goiter with no suspicious features. Bone marrow examination was normal.

A biopsy of the cerebellar lesion was performed in February 2012. The overall appearances were those of an active demyelinating process in the white matter. Inclusions positive for SV40, a polyomavirus protein, were present within oligodendrocytes, in keeping with JC virus–induced demyelination. There was no evidence of co–existent neoplastic processes in the biopsy. A diagnosis of progressive multifocal leukoencephalopathy (PML) was made. Following the brain biopsy she spontaneously improved without specific treatment. On review in December 2012 she was found to have residual left sided ataxia with occasional myoclonic jerks, but she was independently mobile and has returned home.

PML rarely occurs in immunocompetent persons. Of these, only a minority remit spontaneously. Thorough investigation to exclude occult and treatable causes of immunosuppression, such as lymphoma, is mandatory in such cases. Patients should be closely monitored for evidence of recurrence, as there appears to be a high risk of relapse in the immunocompetent, presumably due to an undetectable deficit in the cellular immune system, i.e. an immunological scotoma.