Psychiatryniche
A 22-year-old woman is admitted with three weeks of rapidly worsening persecutory beliefs and speech that is increasingly hard to follow. In the last week her family have noticed her lips and jaw moving constantly in chewing motions she cannot stop, and she has had two witnessed generalised convulsions. Her pulse swings between 50 and 140/min and her temperature between 36 and 38.5 degrees Celsius. She has never taken an antipsychotic. Computed tomography of the brain, full blood count, electrolytes, liver biochemistry and a urine drug screen are all normal. Which one of the following investigations should be arranged next?