Introduction: Osmotic demyelination syndrome (ODS) is increasingly recognized to involve extrapontine locations in addition to the better-known central pontine myelinolysis.
Aims: This study describes clinical and radiological features of consecutive patients with ODS detected over 1 year.
Methods: Patients fulfilling clinical and radiological criteria for ODS were prospectively enrolled and were followed with serial assessments during hospital stay and up to 253 days after discharge.
Results: Eight patients (five females) aged 24-89 years were enrolled, comprising 0·06% of all admissions to the general medical and neurology services. All had preceding hyponatraemia and hypokalaemia of various aetiologies. One patient developed ODS after postpartum pituitary haemorrhage, which has been reported only rarely. Sodium levels were corrected at maximal rates exceeding 8 mmol/l/day. Neurological symptoms attributed to ODS began 3-15 days after clinical improvement following sodium correction in four patients; the remainder did not show any intervening lucent interval. Fifty per cent were stuporous at admission, 50% had seizures, 62·5% had symmetric parkinsonism, and 75% had prominent primitive reflexes. Stretch reflexes were absent in 25% and normal or brisk in the remainder. Magnetic resonance imaging (MRI) showed symmetric striatal lesions in all patients, with concomitant pontine involvement in only 25%. Four patients had poor outcomes (modified Rankin score >3), with prognosis dependent on the presence of severe systemic illness, liver dysfunction, encephalopathy, seizures, and degree of disability upon discharge from hospital. Patients with parkinsonism responded to dopaminergic therapy, with chorea, dystonia, and depression as later developments. This series is remarkable for the high incidence of extrapontine lesions, much more common than pontine involvement.