As shown in the above quotation from Jean-Martin Charcot's teaching of the late 19th century, the concept of atypical Parkinsonian disorders and formes frustes of the classic disease emerged in parallel with the definition of Parkinson's disease itself. In 1817, James Parkinson, a London general practitioner, described resting tremor and gait impairment in the small sample of subjects whose symptoms would later be coalesced into a disorder that would bear his name (2). Nearly 50 yr later, Charcot returned to this early description and used his large patient population to study Parkinson's disease in full detail. With access to thousands of elderly patients who lived in the sprawling hospitalcity of the Hopital de la Salpetriere in central Paris, Charcot studied the evolution of signs from very early disease through the most advanced stages (3,4). Charcot used specialized recording equipment to distinguish the rest tremor of typical Parkinson's disease from the tremors typical of multiple sclerosis and other conditions where posture- or action-induced exacerbation occurred (5). He was particularly adept in distinguishing bradykinesia as a cardinal feature of the illness and separating it from weakness. These studies led him to discourage the original designation of paralysis agitans, because patients did not develop clinically significant loss of muscle power until very late. Charcot further emphasized the distinctive elements of rigidity and delineated its distinction from spasticity or other forms of hypertonicity. Finally, he succinctly described the stance and gait of the subject with Parkinson's disease:
His head bends forward, he takes a few steps and they become quicker and quicker to the point that he can even bump into the wall and hurt himself. If I pull on his trousers from behind, he will retropulse in the same distinctive way (4).
From: Current Clinical Neurology: Atypical Parkinsonian Disorders Edited by: I. Litvan © Humana Press Inc., Totowa, NJ
Charcot's celebrated teaching courses and publications established these four features—rest tremor, bradykinesia, rigidity, and postural reflex impairment in balance and stance—as the cardinal features of typical Parkinson's disease. Charcot complemented these studies with documentation of trophic and arthritic features of the illness, with further studies of pain and autonomic nervous system alterations, and with pharmacological observations (3). At the same time, however, as indicated in the introductory quotation of this chapter, he emphasized the importance of recognizing cases that he termed variants or formes frustes, cases that were similar to and yet distinct from the classic, archetypal form of the disease. These cases were termed atypical Parkinson's disease, at a time when the pathological substrate of Parkinson's disease itself remained unknown. As a historical introduction to the conditions that are the primary focus of this book and today collectively termed atypical par-kinsonian disorders, these historical cases provide source material for the early study of conditions later to be separated from Parkinson's disease and defined in the mid- and late-20th century as progressive supranuclear palsy, multiple system atrophy, and corticobasal degeneration.
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