CJD is a fatal brain disease first classified in the 1920s. In 1996, doctors reported a variant of the disease, vCJD. Research since suggests that vCJD is the result of exposure to the agent that causes Bovine Spongiform Encephalopathy (BSE) in cattle. This section contains guidance on CJD in general, investigations into vCJD and the possible CJD link, and information about the work of the Department of Health's CJD policy unit...
The age of onset is generally different in variant and sporadic CJD. Variant CJD has tended to affect younger individuals with an average age of onset of around 27. Sporadic CJD has tended to affect middle-aged and elderly individuals. However, this difference is not absolute. There are those with variant CJD with a relatively older onset (including one case aged 74). Sporadic CJD may also affect very young individuals on occasions, including those in their teens and twenties. There is therefore a small overlap in the age group affected by variant CJD and sporadic CJD. The age of an individual is not an absolute guide to the type of CJD.
The duration of illness is generally different in variant CJD and sporadic CJD. Many cases of variant CJD have durations of a year or more. The duration of sporadic CJD is typically a few months, and, in a few cases, a few weeks. However, there is again no absolute distinction. There are cases of variant CJD who have died after an illness of only a few months and there are occasional cases of sporadic CJD with durations of one or two years or even longer. Therefore, the duration of illness is not an absolute guide to the form of CJD.
The symptoms of sporadic and variant CJD tend to be different. In particular, sporadic CJD tends to present with a clearly neurological illness that follows a very rapidly progressive course. In variant CJD, the initial presentation is often with psychiatric or behavioural symptoms and it may not be clear that the individual has neurological illness until several months after the onset. An experienced neurologist can generally distinguish the clinical patterns of sporadic and variant CJD. However, there is some overlap in the symtpoms of the two forms, and, on occasions, it may be difficult to be certain as to the classification of the type of CJD if this were based on the clinical symptoms alone.
Some investigations which are undertaken in CJD may be of great help. In particular, the EEG and the MR scan may be useful. The EEG shows a typical pattern in the majority of cases of sporadic CJD. This typical abnormality has never been seen in variant CJD. The cerebral MRI shows a typical abnormality in the majority of cases of variant CJD which has not been seen in sporadic CJD.
The neuropathological features of variant and sporadic CJD are different. In determining whether an individual has CJD or not, the only absolute test at present is that of neuropathology. Therefore, if an individual has not had neuropathology undertaken on either a brain biopsy in life or at a post mortem, then one cannot be absolutely sure as to the diagnosis. In addition, the neuropathological features of sporadic CJD and variant CJD are quite distinct and this would represent the main definitive method of distinguishing between this two forms of CJD.
There are individuals who do not undergo brain biopsy in life and do not have an autopsy. These individuals may be diagnosed on the basis of "probable sporadic CJD" or "probable variant CJD". Although this does not represent an absolutely definitive diagnosis , if an individual is considered as having "probable" CJD, then it is very likely indeed that this is what they had. Probable sporadic CJD carries a certainty of around 95% or more. To date, all the individuals who have been diagnosed as probable variant in life , who have subsequently had an autopsy have been found to have had variant CJD. http://www.cjd.ed.ac.uk/cjdtype.htm#sporadic