Increasing attention has been paid to the prominence of myoclonus in Alzheimer's disease of early onset. This was particularly striking in many family members affected by autosomal dominant Alzheimer's disease linked to chromosome 14, as recently reported by Haltia and colleagues { 11 and by Lampe and associates [2] and discussed in the editorial by Bird [3].
Here onset was in the fourth or fifth decade with the presenting feature being cognitive decline with prominent seizures and myoclonus. In the differential diagnosis they emphasized Jakob-Creutzfeldt disease.
We recently encountered 2 sporadic patients with progressive myoclonus epilepsy and dementia beginning around age 30 years, in whom the differential diagnosis included Kufs' disease, myoclonic epilepsy and ragged-red fibers (MERRF), and the extremely rare disorders late-onset Lafora disease and atypical inclusion body disease [41. To our surprise, Alzheimer's disease was diagnosed by brain biopsy in 1 and autopsy in the other.
Depending on the mode of presentation, such rare patients may be referred to epileptologists or behavioral neurologists. Epileptologists must now consider Alzheimer's disease in the differential diagnosis of adult-onset progressive myoclonus epilepsy, a syndrome where seizures and myoclonus are usu- ally the presenting manifestations but where cognitive impairment also occurs. Behavioral neurologists should consider the aforementioned disorders in sporadic or familial cases of early dementia with myoclonus. In particular, families with dominantly inherited dementia and myoclonus should not be assumed to have Alzheimer's disease, as Kufs' disease can show autosomal dominant inheritance, and MERRF with maternal inheritance can mimic autosomal dominant transmission [4].