(See also Overview of Prion Diseases.)
Fatal insomnia has two forms:
Fatal familial insomnia and sporadic fatal insomnia differ from other prion diseases because they affect predominantly one area of the brain, the thalamus, which influences sleep.
In fatal familial insomnia, symptoms may begin in a person's late 20s to the early 70s (average is 40 years). Death usually occurs 7 to 73 months after symptoms begin. The sporadic form begins slightly later, and life expectancy is slightly longer.
In the familial form, early symptoms include minor difficulties falling and staying asleep and occasional muscle twitching, spasms, and stiffness. During sleep, people may move a lot and kick. Eventually, they cannot sleep at all. Later, mental function deteriorates and coordination is lost (called ataxia). The heart rate may become rapid, blood pressure may increase, and people may sweat profusely.
In the sporadic form, early symptoms include a rapid decline in mental function and loss of coordination. People with this form may not report sleep problems, but sleep studies can detect abnormalities.
Doctors consider fatal insomnia as a rare possible diagnosis when people have typical symptoms, such as rapidly deteriorating mental function, loss of coordination, and/or sleep problems. The following are done to confirm the diagnosis:
The diagnosis of fatal familial insomnia is confirmed by genetic testing.