Patients with late onset of PD tend to have an accelerated evolution of the disease, thus cognitive and functional decline may manifest more rapidly and intensely. This phenomenon results from a swift neurodegenerative process in the brain.
Regarding clinical manifestations, patients with predominant rigidity, postural instability and gait difficulty usually have faster disease progression and tend to be more cognitively impaired; on the other hand, those with tremor predominance tend to have slower illness progression and a more preserved cognition.1 Several earlier studies have showed association between cognitive decline and rigidity or instability.1,5,14,31,32 Moreover, Jankovic & Kapadai1 found that the tremor subtype of PD was associated with preserved mental condition, earlier age at onset and slower progression of the disease in comparison with postural instability and gait difficulty, which were associated with cognitive impairment, more severe bradykinesia, and a more rapid progression of PD. In addition to postural instability and gait disturbances, Emre et al.14 and Burn et al.32 found an association between rigidity and cognitive impairment in patients with PD. Evolution of dementia in patients with more severe motor symptoms such as postural instability and gait difficulty have been associated to rate of neurodegeneration and cell loss in several neurochemical systems, in addition to more rapid cognitive decline.32