Sporadic fatal insomnia masquerading as a paraneoplastic cerebellar syndrome.

Background: Sporadic fatal insomnia is a rare prion disease that has recently been recognized.

Objective: To report a unique case of sporadic fatal insomnia in a woman with progressive cerebellar deterioration who was originally thought to have a paraneoplastic cerebellar syndrome.

Design: Case report describing a patient with autopsy-proven sporadic fatal insomnia.

Patient: A 56-year-old woman with progressive cerebellar ataxia who was found to have a retroperitoneal non-Hodgkin lymphoma.

Results: Autopsy demonstrated marked degenerative changes in the thalamus, cerebellum, and inferior olivary nucleus. A mild spongiform change was present in the thalamus and cortical gray matter. Western blot analysis confirmed the presence of abnormal, protease-resistant prion protein (PrP(Sc)), characteristic of sporadic fatal insomnia.

Conclusions: Clinicians should be aware of this rare prion disease and should strongly consider the importance of autopsy toward the investigation of unusual neurological diseases.