Dissecting parkinsonism: cognitive and gait disturbances

Parkinsonism is usually designated a movement disorder. However, cognitive impairment comprises a major part of many parkinsonian syndromes, and inversely correlates with quality of life. Parkinsonian features are largely attributed to subcortical dopaminergic dysfunction, although other brain regions and neurotransmitters also contribute. This is illustrated by phenotypic differences among different parkinsonian syndromes. Slowed processing speed and executive dysfunction are generally expected in parkinsonian patients, but additional cognitive features can suggest specific pathological substrates, e.g. apraxia in corticobasal degeneration. Similarly, motor symptoms generally include combinations of bradykinesia, rigidity, rest tremor, and postural instability, although nuanced differences and associated clinical features often help differentiate between parkinsonian syndromes. Human gait requires complex synchronisation at every level of the nervous system, yet occurs with minimal conscious effort on behalf of the walker. Deviations from the normal gait pattern can result from otherwise unnoticeable insults to the body, both intrinsic and extrinsic to the nervous system. Gait is almost always abnormal in parkinsonism, ranging from subtle arm swing asymmetry to discrete episodes of gait freezing. Moreover, one's cognitive state can directly affect one's quality of gait. The notion that a gait profile could in fact be a disease-specific biomarker is an area of great research interest. This review focuses on the manifestations of, and correlations between, cognitive and gait impairment in common parkinsonian conditions, and provides guidance for a clinical approach to assessing them.