Case presentation

A 41-year-old man presented in May 2023 with a new-onset episode of generalised seizure and postictal confusion. He became restless and irritable at the emergency department, with nausea and vomiting. Over the previous 10 days, he had developed a fever and for 5 days had experienced new-onset intermittent headaches and fatigue. He had a history of hypertension but was otherwise well.

On examination, he was febrile to 37.6℃ with mildly elevated blood pressure (144/80 mmHg) but normal oxygen saturation (96%). His Glasgow Coma Scale score was 11 (eye 3, verbal 3, motor 5). He was disorientated, unable to follow commands and spoke disorganised words. He could localise to noxious stimuli in all limbs. Muscle strength, tone and reflexes were normal throughout with flexor plantar responses. There was no neck stiffness or asterixis.

Initial investigations showed leucocytosis of 18.7×10⁹/L (4.0–11.0) with 83.3% neutrophils and elevated C reactive protein at 12.9 mg/L (<10) along with mildly elevated transaminases. He had severe hypokalaemia at 2.4 mmol/L (3.5–4.9) but no endocrine, urinary or coagulation abnormalities. Autoimmune serological screening was negative, and serology for HIV and syphilis was negative. CT scan of chest showed bilateral interstitial pneumonia (figure 1A). Contrast-enhancement MR scan of brain showed a dilated left lateral ventricle without parenchymal and leptomeningeal abnormalities (figure 1B–C). Continuous electroencephalogram (EEG) showed mid-amplitude theta slowing over the frontocentral and temporal region with a frontal dominance, suggesting encephalopathy (figure 1D).

Questions for consideration

What is the differential diagnosis?

The differential diagnosis is broad for a patient …