An increase in motor problems like those seen in Parkinson’s disease is associated with the development of Alzheimer’s disease in old age, according to a study in the April issue of The Archives of Neurology.
According to the study, signs similar to those seen in people with Parkinson’s disease (PD), including irregular gait, rigidity, tremor and limited movement, are common in older people without AD, and the presence of these signs may be linked to the development of AD. However, the progression and severity of these signs and subsequent development of AD has not been studied.
Robert S. Wilson, PhD, and colleagues of Rush-Presbyterian-St. Luke’s Medical Center studied the association of the progression of parkinsonianlike signs with the development of AD and cognitive decline. The researchers studied 824 older Catholic clergy members (average age at the beginning of the study was 75.4 years) without any clinical evidence of AD or PD at the beginning of the study. The participants had annual clinical exams and completed a modified version of the Unified Parkinson’s Disease Rating Scale (UPDRS, a test that measures signs of PD), detailed cognitive testing and testing for signs of AD. Participants were followed up for an average of 4.6 years, with some studied for up to 8 years.
The researchers found that over the average follow up time of 4.6 years, 114 participants developed AD. The UPDRS scores increased (indicating a worsening of parkinsonianlike symptoms) in 79 percent of participants, who were divided into groups with the least, moderate or most rapid progression. The researchers found that compared with the 21 percent without progression, the risk of AD more than doubled in the subgroup with the least progression, more than tripled in the moderate subgroup, and increased more than 8-fold in the subgroup with the most rapid progression.
The researchers report that the effect was mostly due to worsening gait and rigidity. They also found that rate of change on the UPDRS measure was inversely associated with the rate of change on tests measuring cognitive function.
The researchers conclude: “In a cohort of more than 700 older persons examined annually for up to 8 years, evidence of parkinsonianlike signs at baseline, as assessed on the UPDRS, was associated with increased risk of incident AD. After controlling for baseline UPDRS, annual rate of progression on the UPDRS was related to disease incidence. Compared with those without progression on the UPDRS, risk of developing AD was increased more than 8-fold in those with the most rapid progression. The results suggest that progression of parkinsonianlike signs in older persons is related to the development of AD.”