Osmotic myelinolysis

Clinical History

A patient presented with a loss of consciousness, and hypotension, and she had a history of chronic alcohol use.

Imaging Findings

A female patient with a history of chronic alcohol use presented to the emergency department after having been found collapsed at her home with a decreased level of consciousness. She was noted to have abnormal level of serum electrolytes. Despite the correction of these biochemical abnormalities, the patient remained drowsy. She underwent an MRI for investigation of her persisting altered mental status.

Discussion

Osmotic myelinolysis may be characterized by pontine and extra pontine demyelination. Extra pontine involvement is now increasingly recognized, and it often occurs without central pontine changes. Noninflammatory, symmetric demyelination may involve the pons, cerebellum, cerebral cortex/subcortex, putamen, caudate nucleus and the thalamus. The exact etiology is not known, but an osmotic shift following rapidly or overly corrected hyponatraemia is often implicated. Osmotic myelinolysis is also seen in patients with chronic alcohol use and in the malnourished without hyponatraemia. Acute brain imaging findings often include a normal CT scan. MRI shows T1 and T2 prolongation within the affected areas. Extra-pontine lesions include the thalamus, deep white matter, and the putamen. Lesions characteristically lack the mass effect or enhancement. Central pontine involvement characteristically spares the peripheral rim. MRI findings may also be normal, with proton MR spectroscopy being the only modality that shows features of myelin breakdown with an increased choline/creatine ratio and elevated lipid peaks. The follow-up MR imaging shows atrophy in the affected regions. The differential diagnosis for brainstem signal changes includes pontine ischaemia/infarction which is often paramedian in location and asymmetric. Primary demyelinating disease such as multiple sclerosis usually shows characteristic lesions in the hemispheric periventricular white matter. Considerations for caudate and basal ganglia changes include Wilson’s disease which may give a similar appearance but tends to involve the basal ganglia more than the pons. Hypertensive encephalopathy occurs when there is an elevation of blood pressure and it may affect the pons together with involvement of the parietal and occipital lobes.

Differential Diagnosis List

Final Diagnosis

Osmotic myelinolysis—extra pontine and central pontine myelinolysis.

URL:	https://www.eurorad.org/case/3057
DOI:	10.1594/EURORAD/CASE.3057
ISSN:	1563-4086