Parkinsonism: heterogeneity of a common neurological syndrome

Parkinsonism refers to a neurological syndrome embracing bradykinesia, muscle rigidity, tremor at rest and impaired postural reflexes, and involving a broad differential diagnosis. Having ruled out secondary causes (most importantly drugs), distinguishing levodopa-responsive idiopathic parkinson's disease (PD) from chiefly treatment-resistant and hence atypical parkinsonism is essential. Recent clinico-pathological studies using data-driven approaches have refined the traditional classifications of parkinsonism by identifying a spectrum of subtypes with different prognoses. For example, progressive supranuclear palsy (PSP), characterised by early vertical gaze limitation and falls, probably has a milder variant with predominant parkinsonism (PSP-P) which may respond quite well to levodopa before converting to the classical disease, relabelled Richardson syndrome (PSP-RS). Analysis of PD subcategories has shown that tremor-dominant forms are probably less benign than was hitherto thought and that in mild cases dystonia should rather be considered. In addition, life expectancy in early onset PD may be shortened. Despite the clinical and pathological overlap of the various subtypes, appreciating the heterogeneity of parkinsonism also includes identifying non-motor features such as early autonomous or cognitive problems which are potentially amenable to pharmacological treatment. Not least, non-motor symptoms, along with postural instability, render the patient particularly vulnerable to side effects, and hence avoiding unnecessary treatment is equally important in the management of parkinsonian disorders.