A 50-year-old, right handed woman presented in January 2009 with a 1-week history of unsteadiness and dysphagia. Three weeks previously, she had a self-limiting flu like illness. Clinically she had a right internuclear ophthalmoplegia (INO), horizontal and upbeat nystagmus, right sided facial weakness of upper motor neuron (UMN) type and asymmetrical spastic quadriparesis, worse on the left. On the sixth day of admission, there was acute deterioration in her consciousness, requiring intensive care admission for airway protection.

The following tests were either normal or negative: routine biochemistry, vitamin B12, folate, lactate, antinuclear antibodies, extractable nuclear antigen antibodies, antineutrophil cytoplasmic antibodies, rheumatoid factor, serum ACE, paraneoplastic antibodies, glycolipid antibodies, cryoglobulins, serum and urine electrophoresis, serology testing including syphilis, HIV, hepatitis B and C. Cerebrospinal fluid (CSF) constituents including virology, cytology and oligoclonal bands were either normal or negative. MRI of the brain showed a non-enhancing high signal change within the right middle cerebellar peduncle extending inferiorly into the dorsal aspect of the brainstem. A small rounded area of signal change was also noted in the left middle cerebellar peduncle. There were a few foci of high signal intensity in the subcortical white matter bilaterally (figure 1).