Growing evidence suggests that Parkinson's disease (PD) often starts with non-motor symptoms that precede diagnosis by several years. In the first study to examine patterns in the quality of life of Parkinson' disease patients prior to diagnosis, researchers have documented declines in physical and mental health, pain, and emotional health beginning several years before the onset of the disease and continuing thereafter. Their results are reported in the latest issue of Journal of Parkinson's Disease.
"We observed a decline in physical function in PD patients relative to their healthy counterparts beginning three years prior to diagnosis in men and seven and a half years prior to diagnosis in women," says lead investigator Natalia Palacios, PhD, Department of Nutrition, Harvard School of Public Health. "The decline continues at a rate that is five to seven times faster than the average yearly decline caused by normal aging in individuals without the disease."
The study included 51,350 male health professionals enrolled in the Health Professionals Follow Up Study (HPFS) and 121,701 female registered nurses enrolled in the Nurses' Health Study (NHS). In both ongoing studies, participants fill out biannual questionnaires about a variety of lifestyle characteristics and document the occurrence of major chronic disease. In the NHS study, questionnaires measured health-related quality of life in eight areas: physical functioning, role limitations due to physical problems, role limitations due to emotional problems, vitality, bodily pain, social functioning, mental health, and general health perceptions. In the HPFS, only physical functioning was assessed.
Researchers identified 454 men and 414 women with PD in the two cohorts. At 7.5 years prior to diagnosis, physical function among PD cases, in both men and women, was comparable to that in the overall cohort. A decline began approximately 3 years prior to diagnosis in men and approximately 7.5 years prior to diagnosis in women. Physical function continued to decline thereafter at a rate of 1.43 and 2.35 points per year in men and women, respectively. In comparison, the average yearly decline in individuals without PD was 0.23 in men and 0.42 in women. Other measures of quality of life, available only in women, declined in a similar pattern.
Dr. Palacios notes that a strength of the study is the availability of prospective data on both PD patients and a healthy comparison group, and the ability to chart the deterioration in functioning and quality of life over the whole study follow-up, which included many years prior to diagnosis.
"This result provides support to the notion that the pathological process leading to PD may start several years before PD diagnosis," says Dr. Palacios. "Our hope is that, with future research, biological markers of the disease process may be recognizable in this preclinical phase."