Fatal insomnia, which includes fatal familial insomnia and sporadic fatal insomnia, are rare hereditary or sporadic prion disorders causing difficulty sleeping, motor dysfunction, and death.
(See also Overview of Prion Diseases.)
Fatal familial insomnia (FFI) results from an autosomal dominant mutation in the PRNP gene (1). Average age at onset is 40 years (ranging from the late 20s to the early 70s). Life expectancy is 7 to 73 months. Early symptoms of FFI include increasing difficulty falling asleep and maintaining sleep, as well as cognitive decline, ataxia, and psychiatric symptoms. Sympathetic hyperactivity (eg, hypertension, tachycardia, hyperthermia, sweating) may occur later.
Sporadic fatal insomnia (sFI) lacks a PRNP gene mutation. Average age at onset is slightly older than FFI, and life expectancy is slightly longer than in FFI. Early symptoms include cognitive decline and ataxia. Sleep abnormalities are not commonly reported but can usually be observed during a sleep study.
Fatal insomnia should be considered as a rare possibility when patients have rapidly progressive cognitive impairment accompanied by behavioral or mood changes, ataxia, and sleep disturbances. Suspicion of FFI or sFI should prompt a sleep study by polysomnography, looking for complete disruption of sleep architecture, and/or brain FDG-PET or SPECT imaging to look for characteristic isolated thalamic hypometabolism (1). Genetic testing can confirm the diagnosis of the familial form. MRI and measurement of 14-3-3 protein and tau in cerebrospinal fluid (CSF) are not useful. CSF RT-QuIC is commonly negative in FI.
There is only supportive treatment for fatal insomnia.
Reference
1. Cracco L, Appleby BS, Gambetti P: Fatal familial insomnia and sporadic fatal insomnia. Handb Clin Neurol 153:271-299, 2018. doi: 10.1016/B978-0-444-63945-5.00015-5
