INTRODUCTION

Prion diseases are neurodegenerative diseases that have long incubation periods and progress inexorably once clinical symptoms appear. Five human prion diseases are currently recognized: kuru, Creutzfeldt-Jakob disease (CJD), variant Creutzfeldt-Jakob disease (vCJD), Gerstmann-Sträussler-Scheinker syndrome (GSS), and fatal familial insomnia (FFI). CJD accounts for more than 90 percent of sporadic prion disease [1].

These human prion diseases share certain common neuropathologic features including neuronal loss, proliferation of glial cells, absence of an inflammatory response, and the presence of small vacuoles within the neuropil, which produces a spongiform appearance.

The clinical manifestations and diagnosis of Creutzfeldt-Jakob disease will be reviewed here. Variant Creutzfeldt-Jakob disease, Kuru, GSS, and FFI, and the biology of prions and the genetics of prion diseases are discussed separately. (See "Variant Creutzfeldt-Jakob disease" and "Diseases of the central nervous system caused by prions" and "Biology and genetics of prions".)

EPIDEMIOLOGY AND RISK FACTORS

Creutzfeldt-Jakob disease (CJD) is the most frequent of the human prion diseases, although it is still rare. Sporadic (sCJD), familial (fCJD), iatrogenic (iCJD), and variant forms of CJD (vCJD) are all recognized. The vast majority of CJD cases are sporadic (85 to 95 percent), while 5 to 15 percent are due to fCJD; iCJD generally accounts for less than 1 percent [2,3].

Approximately one case of sporadic CJD occurs per 1,000,000 population per year with a worldwide distribution. The mean age for the onset of disease is between 57 and 62 years, although rare cases in young adults and those over 80 years of age have been described [3-7]. Patients with vCJD and iCJD tend to be much younger, which led to an early appreciation that the mode of transmission might be different. fCJD patients have only a slightly younger age of onset compared with sCJD [8]. There is no gender predilection for CJD. In the United States, the incidence of CJD appears to be less in African Americans, American Indians, and Alaska natives compared with the white population, however this observation may have resulted from ascertainment bias [9,10].