Is there a need to redefine Parkinson's disease?

Parkinson's disease (PD) has initially been described as a clinical syndrome, although the exact definition has changed over the past centuries. The inclusion of the pathological changes added another level of complexity, with Lewy bodies, synuclein deposits and neuronal loss in the substantia nigra being used alternatively. A third level of complexity was added with the recognition of genetic mutations resulting in parkinsonism, sometimes with and sometimes without Lewy body deposition, and the identification of frequent additional important pre-motor manifestations. These different points of view on the definition of PD have important implications on the study of the etiology and even the therapy of PD.