Recent developments in the neuropathological diagnosis of Parkinson's disease and parkinsonism

The diagnosis of Parkinson's disease (PD) is based mainly on clinical criteria. Large clinicopathological studies reveal however a different diagnosis in up to 25% of the cases (Hughes et al., 1992). Recent advances in molecular biology have shown that some proteins, especially tau and alpha-synuclein, play an essential role in the pathogenesis of parkinsonian and dementing disorders. Such diseases are now classified as tauopathies and synucleinopathies. Progressive supranuclear palsy and corticobasal degeneration are the major tauopathies. To the synucleinopathies belong PD, Lewy body dementia and multiple system atrophy. In pathological conditions abnormal proteins will aggregate in neurons and glial cells and form inclusion bodies. Lewy bodies are the hallmark of Parkinson's disease and Lewy body dementia. Identification of these inclusions and other specific lesions in parkinsonian disorders is facilitated by the routine application on formalin fixed brain of immunohistochemistry for alpha-synuclein, tau and ubiquitin. The purpose of this paper is to briefly review and illustrate the value of these new techniques in the postmortem diagnosis of parkinsonian disorders. Neuropathological examination of the brain is however time consuming and immunohistochemistry represents additional costs. As the selection of brain samples for microscopical examination and antibodies for immunohistochemistry depends on the underlying pathology, some clinical information should be provided to the pathologist such as the clinical diagnosis and when indicated the results of brain imaging studies. A close co-operation between the neurologist and neuropathologist is thus essential to select the most appropriate brains for complete neuropathological investigation.