Brain biopsy in Creutzfeldt–Jakob disease: evolution of pathological changes by prion protein immunohistochemistry

The formation of protease‐resistant prion protein (PrPsc) is considered to be an early event in the pathogenesis of Creutzfeldt–Jakob disease (CJD) and hence its demonstration in brain biopsies by immunohistochemistry is considered diagnostic. We analysed eight brain biopsies from the frontal cortex collected from different parts of India from cases diagnosed as CJD on clinical and pathological grounds for the expression of prion protein (PrP). The duration of illness in these cases varied from 2 months to 1 year. Immunohistochemistry was carried out on paraffin sections using two different clones (KG9 and 3F4) of monoclonal antibodies to PrP. Although all eight cases showed classical features of spongiform encephalopathy of varying severity, only five of the eight cases revealed PrPsc in the brain tissue. The immunolabelling was focal and all areas with spongiform change were not labelled. A temporal evolution in the staining pattern was evident – particulate diffuse labelling (synaptic type) in early stages (2 months), perivacuolar deposits in intermediate stages (5–6 months), and dense plaques in late stages (12 months).