Reversible splenial lesion syndrome with a hyperosmolar hyperglycemic state and neuroleptic malignant syndrome caused by olanzapine

A 27‐year‐old woman with panic disorder taking 20 mg olanzapine daily for 4 months was admitted to Mito Kyodo General Hospital, Mito, Ibaraki, Japan, because of disturbed consciousness with fever, hyperglycemia, hyperosmolarity and elevated creatine phosphokinase. She was diagnosed with a hyperosmolar hyperglycemic state and neuroleptic malignant syndrome. Brain magnetic resonance imaging showed transiently restricted diffusion in the splenium of the corpus callosum, with a high signal intensity on diffusion‐weighted imaging. The neurological abnormalities disappeared along with improvement of metabolic derangements, and the follow‐up magnetic resonance imaging carried out on the 26th day of admission showed complete resolution of the lesions in the splenium of the corpus callosum. These clinical and radiological features are highly suggestive of clinically mild encephalitis/encephalopathy with a reversible splenial lesion. The first case of mild encephalitis/encephalopathy with a reversible splenial lesion caused by olanzapine‐induced hyperosmolar hyperglycemic state and neuroleptic malignant syndrome is reported.