BACKGROUND: Sporadic fatal insomnia (sFI) and fatal familial insomnia (FFI) are 
rare human prion diseases.
CASE PRESENTATION: We report a case of a 33-year-old female who died of a prion 
disease for whom the diagnosis of sFI or FFI was not considered clinically. 
Following death of this patient, an interview with a close family member 
indicated the patient's illness included a major change in her sleep pattern, 
corroborating the reported autopsy diagnosis of sFI. Genetic tests identified no 
prion protein (PrP) gene mutation, but neuropathological examination and 
molecular study showed protease-resistant PrP (PrPres) in several brain regions 
and severe atrophy of the anterior-ventral and medial-dorsal thalamic nuclei 
similar to that described in FFI.
CONCLUSIONS: In patients with suspected prion disease, a characteristic change 
in sleep pattern can be an important clinical clue for identifying sFI or FFI; 
polysomnography (PSG), genetic analysis, and nuclear imaging may aid in 
diagnosis.