A 74-year-old male with a history of hypertension treated with diuretics presented at the emergency department complaining of generalized weakness over the past week. Clinical examination revealed that the patient was lethargic with a blood pressure of 140/80 mm Hg. Blood investigations detected serum sodium of 97 mEq/L and potassium of 3.1 mEq/L. Four days after sodium correction, the patient developed dysarthria, quadriparesis, and impaired consciousness, requiring endotracheal intubation. T2-weighted and FLAIR brain MRI showed hypersignal in the central pons and bilateral striatum, without gadolinium enhancement, consistent with central pontine and extrapontine myelinolysis (Fig. 1). After 1 month, he was able to walk without ventilatory support and showed normal performance on bedside mental status testing. Approximately 6 months later, he gradually developed generalized chorea, mainly in the lower limbs. There was no exposure to neuroleptic medications. He was treated with risperidone (1 mg/day) and responded well (see Video).
Figure 1. Brain MRI with central pontine and extrapontine myelinolysis. (A and B) Axial FLAIR images showing characteristic hyperintensity in the central pons with corresponding (C) coronal T2-weighted view. (D) Axial FLAIR image showing symmetric hyperintense abnormalities in putamen (arrow) and head of the caudate nuclei with corresponding (E and F) coronal T2-weighted view.
This case supports the notion of CPM and EPM being part of a clinical spectrum with overlapping features. Our patient presented initially with the symptoms of CPM, exhibiting lethargy, quadriparesis, and dysarthria. His subsequent clinical course was characteristic of EPM with the development of an unusual extrapyramidal manifestation, a choreic syndrome. Differential diagnoses of choreic movements, such as tardive dyskinesia, hyperglycemia, stroke, and loss of proprioception, were ruled out.
Osmotic demyelination syndromes (ODS) are becoming increasingly reported. Recent evidence suggests that the distinctive clinical, pathological, and radiological features of ODS may not be as characteristic as initially believed, and that the clinical syndrome of ODS may be expanding to include a wider variety of patients. Early reports stressed the rarity of extrapyramidal symptoms in ODS, often thought to be masked by corticospinal or brainstem dysfunction, but noted delayed development of tremor, rigidity, bradykinesia, dystonia, choreoathetosis, and released reflexes that manifested 10 to 150 days after ODS begins.[4, 5] Extrapontine sites most frequently involve the cerebellum (55%), lateral geniculate body (41%), putamen (34%), thalamus (34%), and cerebral cortex/subcortex (34%).[6, 7] MRI has enabled ante-mortem diagnosis of ODS and has expanded its clinical spectrum with the detection of many mild, atypical, or asymptomatic cases. Microscopically, the lesion shows degeneration and loss of oligodendrocytes with preservation of axons, unless the lesion is very advanced. The presence of extrapyramidal signs is reported in up to 60% of EPM cases, particularly parkinsonism and dystonia. Few cases of chorea after EPM have been reported,[4, 8-10] typically with onset weeks to months later possibly resulting from alterations in the rate or pattern of activity in thalamic, pallidal, subthalamic, or cortical neurons in response to an ineffective neuronal repair, leading to an aberrant neuronal reorganization after recovery from a severe akinetic-rigid state. Our case had predominant involvement of the head of the caudate nucleus and the lateral putamen, an unusual distribution, when compared to previously reported cases of EPM. A bilateral striatum lesion possibly resulted in variable dysfunctions of both direct and indirect striatopallidal pathways, leading to increased thalamocortical drive and hyperkinetic movement, which had a good response to neuroleptic administration (risperidone).