Lessons of the month: Not just morning sickness.

A 34-year-old woman (gravida 4; para 3) at 17 weeks of pregnancy presented with abnormal behaviour for 3 weeks associated with difficulties in walking. She had been admitted 2 months prior with hyperemesis gravidarum and was also diagnosed with thyrotoxicosis. Vomiting and poor oral intake persisted after discharge. She was euthyroid otherwise. Clinical examination revealed a dehydrated and confused patient. She had nystagmus and ataxic gate. Magnetic resonance imaging of the brain showed symmetrical signal changes of posteromedial part of thalamus. A diagnosis of Wernicke's encephalopathy (WE) was made and intravenous thiamine was given leading to gradual improvement of symptoms. Her thyroid function test normalised without any treatment. WE can occur in severe hyperemesis gravidarum. Prompt recognition of WE and replacement with thiamine is important to prevent neurological sequelae and mortality. Gestational transient thyrotoxicosis, which is self-limiting, is more prominent in patients with hyperemesis gravidarum and requires only symptomatic treatment. © Royal College of Physicians 2020. All rights reserved.