Clinical-- subacute progressive ataxia and dysarthria. May in some cases have other brainstem features or cognitive symptoms. These include facial paresthesias, diplopia, dysgeusia and myelopathy.
MRI- 1. numerous nodular or punctate enhancing lesions bilaterally in at least 2 of 3: pons, cerebellum, brachium pontis 2. Individual lesions are small but may coalesce to form larger lesions (mass effect has never been reported) 3. Lesions may occur in spinal cord, basal ganglia nad cerebral white matter but should be less dense the further from the pons 4. Absent features: restricted diffusion on DWI, marked hyperintensity on T2, abnormal cerebral angiogram
Corticosteroid responsiveness-- prompt and significant clinical and radiographic response to steroids-- with relapse when steroids are withdrawn or fell below 20 mg po daily. Uncertain: elevated IgE in some patients is reported as are oligoclonal bands.
Histopathology--- a. white matter perivascular lymphohistiocytic infiltrate with or without parenchymal extension b. infiltrate contains predominant CD+ and CD4+ lymphocytes c. absent monoclonal or atypical lymphocyte population , necrotizing giant cells or granulomas, or histologic features of vasculitis such as destruction of vessel wall, fibronoid necrosis, leukocytoclasia, fibrin thrombi.
Exclusion of mimicking diseases including sarcoid, neuro-Behcet's, vasculitis and lymphoma, glioma, histiocytosis, multiple sclerosis, autoimmmune disorders, Bickerstaff's encephalitis.