Serial positron emission tomographic findings in an atypical presentation of fatal familial insomnia.

BACKGROUND

Genetic analyses of fatal familial insomnia, a prion disease, disclose a broader range of symptoms than previously described. Although insomnia and dysautonomia have been described as hallmarks of the disease, there is substantial variability in clinical presentation.

OBJECTIVE

To evaluate serial fluorodeoxyglucose positron emission tomographic and electroencephalographic findings in atypical fatal familial insomnia without clinical insomnia.

PATIENT

A 63-year-old man who had a history of gait ataxia developed rapidly progressive dementia with mild dysautonomic features. Genetic investigation confirmed diagnosis of fatal familial insomnia (D178N mutation of the prion protein gene and Val/Met polymorphism on position 129 of the mutated allele) with typical neuropathologic findings.

RESULTS

Clinical signs were not specific. An electroencephalogram showed scanty triphasiclike elements and general slowing. We found thalamic hypometabolism in positron emission tomographic scans to be present in a very early stage with progressive deterioration, and patchy cortical alterations showing progression over 6 months.

CONCLUSIONS

In the absence of clear clinical signs, an electroencephalogram was of major diagnostic value, although its specificity in fatal familial insomnia is under debate. Selective thalamic hypometabolism seems to be an early marker in fatal familial insomnia, while cortical changes vary with clinical presentation and stage.