When cjd is such a rare disease, why would a doctor declare a cjd diagnosis without a biopsy? father had seizures, false positive prion test, dementia

Creutzfeldt-Jakob Dz: The only currently available way to definitively diagnose creutzfeldt-jakob disease is brain biopsy or autopsy. Doctors are trying develop a spinal fluid test to detect a specific protein marker for neuronal degeneration -- easier than a brain biopsy, but it has a 5-10% false positive rate. http://www.ninds.nih.gov/disorders/cjd/detail_cjd.htm his history & exam must have been very convincing?

CJD / prion disease: In the USA we have about 3000 autopsy confirmed cases of CJD a year. There is a characteristic "periodic" pattern on EEG, Myoclonus and variable clinical course. Autopsy confirmation is the gold standard. In the 5 cases I've seen all the patients had limb apraxia. I've never had much faith in the CSF prion protein assays.

What is a diagnosis: There is a difference between a confirmed diagnosis and a clinical diagnosis. Sometimes a clinical diagnosis is made, without confirmation. For many illnesses, there is no confirmatory test. Most people determine CJD with spinal fluid testing, a biopsy, or autopsy.