Classic CJD is a human prion disease. It is a neurodegenerative disorder with characteristic clinical and diagnostic features. This disease is rapidly progressive and always fatal. Infection with this disease leads to death usually but not always within 1 year of onset of illness.

Important Note: Classic CJD is not related to "mad cow" disease.
Classic CJD also is distinct from "variant CJD", another prion disease that is related to BSE.

Please see the links below for more information.

• Mad Cow Disease, aka Bovine Spongiform Encephalopathy (BSE)
• Variant Creutzfeldt-Jakob Disease (vCJD)

Occurrence and Transmission

Classic CJD has been a recognized disease since the early 1920s. The most common form of classic CJD is believed to occur sporadically in both genetically predisposed individuals and in random persons, and is caused by the spontaneous transformation of normal prion proteins into abnormal (mutated) prions. This disease occurs worldwide at a rate of approximately one case per 1 million individuals per year, although rates of up to two cases per million are not unusual. The risk of CJD increases with age. In persons aged over 50 years, the annual rate is approximately 3.4 cases per million, slightly elevated compared to the norm. In recent years, the United States has reported fewer than 300 cases of CJD a year.

Whereas the majority of cases of CJD (about 85%) occur sporadically, a smaller proportion of patients (5-15%) develop CJD because of inherited mutations of the prion protein gene. These inherited forms include Gerstmann-Straussler-Scheinker syndrome and fatal familial insomnia.

Clinical and Pathologic Characteristics of Classic CJD

Classic CJD characteristics in comparison with variant CJD, are presented in the table below:

Clinical and Pathologic Characteristics Distinguishing Classic CJD from Variant CJD

Characteristic	Classic CJD	Variant CJD
Median age at death	68 years	28 years
Median duration of illness	4-5 months	13-14 months
Clinical signs and symptoms	Dementia; early neurologic signs	Prominent psychiatric/behavioral symptoms; painful dyesthesiasis; delayed neurologic signs
Periodic sharp waves on electroencephalogram	Often present	Often absent
"Pulvinar sign" on MRI*	Not reported	Present in >75% of cases
Presence of "florid plaques" on neuropathology	Rare or absent	Present in large numbers
Immunohitochemical analysis of brain tissue	Variable accumulation	Marked accumulation of protease-resistance prion protein
Presence of agent in lymphoid tissue	Not readily detected	Readily detected
Increased glycoform ratio on immunoblot analysis of protease-resistance prion protein	Not reported	Marked accumulation of protease-resistance prion protein
Source: Adapted from Belay E., Schonberger L. Variant Creutzfeldt-Jakob Disease and Bovine Spongiform Encephalopathy. Clin Lab Med 2002;22:849-62.
*An abnormal signal in the posterior thalami on T2- and diffusion-weighted images and fluid-attenuated inversion recovery sequences on brain magnetic resonance imaging (MRI); in the appropriate clinical context, this signal is highly specific for vCJD.

Date:June 29, 2005
Content source: National Center for Infectious Diseases