The radiological appearances were considered most compatible with progressive multifocal leukoencephalopathy (PML). This is typified by the confluent asymmetric white matter abnormalities, with U-fibre involvement. Neurosarcoidosis remained in the differential, particularly given the known extra-CNS disease, but there was no enhancement or meningeal involvement evident.
Multiple CSF results were returned negative for John Cunningham virus (JC virus).
There was a clinical deterioration predominantly affecting speech fluency and processing (ACE 64/100).