Central pontine myelinolysis

Clinical History

An alcoholic patient presenting in a drowsy, lethargic state with a low serum sodium.

Imaging Findings

A patient, with a known history of alcohol abuse, was brought to the accident and emergency department in a drowsy, lethargic state. The Glasgow coma scale score at the time of admission was 10. Neurological examination was grossly intact. Biochemistry showed a moderately low serum sodium. A careful correction of serum sodium levels was initiated according to international guidelines.

A CT brain scan at the time of admission was normal. After an initial improvement over the first 2 days, the patient then became more drowsy and developed a pseudobulbar palsy. A second CT brain scan was normal. MRI at this time showed diffuse pontine signal abnormality consistent with central pontine myelinolysis. The patient showed residual pseudobulbar palsy at 1-month follow-up.

Discussion

Central pontine myelinolysis is a demyelinating disease of the pons which may be associated with demyelination elsewhere in the central nervous system. The condition is characterised by loss of myelin and oligodendroglia in the central pons. There are no inflammatory changes, and blood vessels are normal. Clinical features usually reflect damage to the descending motor tracts and include spastic teraparesis, pseudobulbar paralysis and the locked-in syndrome. As clinical findings are not specific, diagnosis relies on a history of deranged sodium metabolism. The stimulus for myelinolysis is usually rapid correction of chronic hyponatraemia, although it can occur with relatively mild osmotic insults. Chronic alcoholism is still the most common underlying condition. Others include diabetes, lung carcinoma, Wilson's disease, trauma, renal insufficiency, haemodialysis and liver transplantation. The clinical picture can vary considerably depending on the degree of CNS involvment.

Radiological findings lag behind and do not necessarily correlate with clinical findings. Imaging studies performed early in the illness may be unremarkable and repeat imaging may be required. CT may show a central pontine region of diminished attenuation, but appearances are often normal. MRI is the imaging modality of choice and shows an area of prolonged T1 and T2 relaxation in the central pons, which may have a characteristic shape. Serial MRI should show a progressive decrease of T2-weighted pontine signal, but this may not fully resolve. MRI changes can mimic multiple sclerosis.

The differential diagnosis of central pontine myelinolysis includes diffuse hypoxic encephalopathy and brainstem and thalamic infarction from thrombosis of the basilar artery; MRI may help to distinguish these entities. A number of therapeutic approaches have been tested, although no specific therapy exists. Correction of serum sodium should not exceed 12mEq/24h. Recovery varies from no improvement to substantial recovery, although the outcome of this condition is frequently fatal.

Differential Diagnosis List

Final Diagnosis

Central pontine myelinolysis

URL:	https://eurorad.org/case/1617
DOI:	10.1594/EURORAD/CASE.1617
ISSN:	1563-4086