A proportion of DLB patients do not suffer from parkinsonism (29%), sometimes even over a prolonged dementia of 5 years or more. However, parkinsonism is more frequently present in DLB than among patients with AD or vascular dementia (VaD) . In the most detailed comparative study of parkinsonism to date, Burn et al.  found that DLB patients had less severe parkinsonism than people with PD-D, but a similar severity of motor deficits compared with PD patients without dementia. The severity of parkinsonism, however, appears to progress similarly in both conditions . The majority of patients with DLB will develop characteristics of parkinsonism, including generalized slowing and postural and gait disturbances . There are some subtle but important differences between DLB, PD-D, and PD in the key parkinsonian signs and symptoms. Postural instability and gait disturbance (PIGD), predominantly mediated by non-dopaminergic lesions, is more pronounced in DLB and PD-D than in PD patients without dementia, whereas the opposite is true for tremor . In addition, parkinsonian features tend to be more symmetrical in PD-D . In a prospective study, those who had PIGD-dominant PD at baseline, or who developed this after having tremor-dominant PD initially, had a higher risk of dementia compared than those who maintained a tremor- dominant phenotype . Importantly, parkinsonism is a key factor explaining the functional impairment in DLB  as well as PD-D.
Cognitive and functional decline
Only one study has directly compared the course of cognitive decline in PD-D and DLB. This study reported that DLB and PD-D patients had a similar rate of decline on cognition over 2 years . There are some indications that the course of disease is more severe in PD-D and DLB than in AD, although few longitudinal comparative studies have been done. The cognitive decline in PD-D  and DLB  seems to be similar to that in AD, but, consistent with the complex clinical symptoms in DLB, functional decline and mortality  progress more rapidly in DLB than in AD.