Teaching Case

Anorexia nervosa. Presented with seizure, a few days later developed mutism, rigidity and agitation. No history of alcoholism.

History of bulimia, presented with seizure and electrolytes corrected too rapidly. A few days later mutism developed, rigidity and agitation. No history of alcoholism. MRI of the brain at the time of presentation was normal. MRI repeated after a week showed high signal in the internal capsule bilaterally with normal pons. Diagnosis of Extrapontine myelinosis was made. Due to further clinical deteriotation MR of brain was again repeated after a week's time. Magnetic resonance imaging of the brain showed prominent high signal seen within the pons, basal ganglia, and thalami on T2-weighted sequence—appearances consistent with osmotic demyelination syndrome (Central and extra pontine myelinosis).

Osmotic demyelination syndrome is a well recognised complication of treatment of patients with severe and prolonged hyponatraemia, particularly when corrected too rapidly. Other conditions associated with an increased risk of the syndrome include chronic alcoholism, malnutrition, prolonged diuretic use, liver failure, receiving an organ transplant, and extensive burns. Extrapontine myelinolysis, with or without pontine involvement, was recognised in 1962 and occurs in at least 10% of patients with central pontine myelinosis, most often in the basal ganglia and thalamus. Although both conditions share the same pathology, the location of the lesions results in different clinical presentations. Classically, central pontine myelinosis is associated with dysarthria and dysphagia, due to corticobulbar fibre involvement, as well as an initially flaccid quadraparesis due to lesions in the corticospinal tract. Extrapontine myelinolysis is characterised by tremor and ataxia and may be associated with movement disorders including mutism, parkinsonism, dystonia, and catatonia. The timing of the appearance of lesions on MRI may be significantly delayed, and if the diagnosis remains likely a repeat imaging study at 10–14 days may reveal lesions not apparent on early scans Diffusion weighted imaging (DWI) findings have been reported. DWI might have the capability of detecting lesions undetectable on T2. A single case report has just been published showing altered DWI in a patient within 24 hours of tetraplegia at a time when conventional MRI findings were inconspicuous. CPM can be seen on CT, but magnetic resonance imaging (MRI) is frequently striking and is the imaging technique of choice, having a greater sensitivity for CPM than CT and superior capacity for the demonstration of the lesions of EPM. Hyperintense lesions are seen on T2, and hypointense lesions on T1 weighted images. The lesions are non-contrast enhancing. The characteristic lesion on MRI involves the entire pons except for a rim of periphery. Radiological differentials include stroke, multiple sclerosis and brainstem glioma. There is no consistent correlation between the persistence of radiographic abnormalities and that of symptoms in surviving patients.