Classical Parkinson disease versus Parkinson complex--reflections against staging and in favour of heterogeneity.

Pathological studies have prompted the idea that Parkinson disease (PD) is a multisystem disorder, which starts far away from the nigrostriatal dopamine system and it goes through a long pre-clinical period. Evidence from epidemiological research, functional imaging, olfaction and sleep studies provides support to this hypothesis. Accordingly, PD is seen as an homogeneous disease which sequentially affects different neural structures leading to a well-defined clinical picture. This concept, recently named PD complex, has deep theoretical and practical implications which raise some concerns. This report shows the concept of classical PD as opposed to PD complex. Although the relevance of the central argument concerning the PD complex concept is admitted, it needs to be fully proved before premature conclusions are drawn. In contrast, the notion of classical and clinically significant PD can explain many of the well-characterized pathological and clinical features of the disease and it gives support to the idea that the magic word in PD is variability.