Tremors and memory symptoms were identified among individuals in a primary care setting as early as 10 years before a Parkinson’s disease diagnosis in a new study.
Most research on the causes and early signs of Parkinson’s disease (PD) have involved patients of Northern European ancestry, Cristina Simonet, MD, of Queen Mary University of London, and colleagues wrote in their paper, published in JAMA Neurology.
Additionally, data on how PD might manifest in different ethnic groups are limited, they said.
In their nested case-control, the researchers examined data from electronic health records of an ethnically diverse population of 1,016,277 adults seen in primary care practices between 1990 and Feb. 6, 2018. They compared individuals with PD with those without PD or other neurologic conditions.
The researchers identified 10 age and sex-matched controls for each PD case, and also conducted an unmatched analysis after adjusting for age and sex. The final study population included 1,055 patients with PD and 1,009,523 controls. The population of PD cases was 15.7% Black, 19.7% South Asian, 50.9% White, and 8.3% other; the population of controls was 13.3% Black, 21.5% South Asian, 43.7% White, and 11.3% other.
“We observed a constellation of symptoms noted by general practitioners up to a decade before diagnosis of PD,” the researchers said. Symptoms were identified across three time intervals (less than 2 years, 2-5 years, and 5-10 years before diagnosis) to better evaluate exposure outcome associations.
In the matched analysis of midlife risk factors, epilepsy showed the strongest association with PD diagnosis across all time periods, and type 2 diabetes or hypertension 5-10 years before diagnosis was associated with later PD.
Prediagnostic signs of PD included both motor and nonmotor manifestations.
The matched analysis revealed a significant increased association between tremor and memory symptoms less than 2 years before diagnosis (adjusted odds ratios of 151.24 and 8.73, respectively) as well as up to 10 years before diagnosis for tremors and up to 5 years for memory symptoms (aOR, 11.4 and 3.09, respectively) in PD patients, compared with controls.
Other strong associations between PD and early nonmotor features in cases, compared with controls, included hypotension (aOR, 6.81), constipation (aOR, 3.29), and depression (aOR, 4.61).
In addition, the researchers found associations for epilepsy that had not been identified in previous studies, and these associations persisted in a replication analysis.
The study findings were limited by several factors, mainly the use of routine primary care data with underascertained factors of interest, and potential mislabeling of PD, the researchers noted. Other limitations included the lack of data on prescription medication for PD, and the recording of memory problems in primary care without supportive testing to confirm cognitive impairment.
The results support a range of comorbidities and symptoms that may present in primary care, and clinicians should consider PD as a possible cause, the researchers wrote.
Make early referral a priority
The study is important because of the lack of diversity in Parkinson’s disease research, lead author Dr. Simonet said in an interview.
“Over the last decade, the global population suffering from Parkinson’s disease has more than doubled,” she said. Causes may include the increasing numbers of older people with longer life expectancy. “However, it seems there are other factors, including environmental, genetic, and lifestyle, that might play a role in increasing the prevalence of Parkinson’s disease.”
“More representative studies, including minority ethnic groups and those living in areas of high social and economic deprivation, are needed,” Dr. Simonet emphasized.
She said that there is little research on the association with epilepsy and hearing loss in early PD, and “for that reason, our results should encourage further studies to confirm a possible link between these manifestations and Parkinson’s disease.”
Early detection may drive better diagnoses
The current study is important for understanding the prediagnostic features and risk factors that may allow for earlier detection of Parkinson’s disease, William Hung, MD, a geriatrics and palliative care specialist of the Icahn School of Medicine at Mount Sinai, New York, said in an interview. “Prior to this study, there was limited understanding of these features.
“One surprise [in the findings] was that ethnicity and socioeconomic deprivation do not appear to be associated with the risk of PD, in contrast to other illnesses such as dementia,” said Dr. Hung. “The array of prediagnostic features associated with PD is not surprising, but nonetheless important for clinicians to know to consider whether PD could be the underlying cause.”
The take-home message for primary care is that “there are features, such as hearing loss, history of epilepsy, autonomic symptoms, motor symptoms, among others, for which clinicians should consider PD as part of the differential diagnosis as underlying cause and consider referral to specialists for diagnostic clarification,” said Dr. Hung.
“Additional research is needed to translate these findings to care, perhaps developing decision aids, interventions that may help with diagnosis and evaluation,” as is work on understanding the link between PD and symptoms such as hearing loss and epilepsy, he said.
Primary care offers opportunity to identify risk factors
The current study represents an important step in early recognition of PD, with implications for helping patients access treatments promptly and improve their quality of life, Bhavana Patel, DO, Shannon Chiu, MD, and Melissa J. Armstrong, MD, of the University of Florida, Gainesville, wrote in an accompanying editorial.
“The primary care setting is commonly where symptoms heralding the onset of PD are first discussed. However, little is known regarding the prediagnostic manifestations of PD that are seen in primary care clinics, particularly in underserved populations,” they wrote.
The study included many risk factors and prodromal markers associated with research criteria for prodromal PD, but did not include several risk and prodromal markers in the Movement Disorders Society research criteria, “such as symptoms suggestive of REM sleep behavior disorder, excessive daytime sleepiness (which overlaps with, but is distinct from, fatigue), urinary dysfunction, pesticide and solvent exposure, caffeine use, level of physical activity, and family history,” they said.
Even in individuals with diagnosed PD, certain symptoms, particularly nonmotor symptoms, are commonly underreported,” and primary care clinicians may not recognize these symptoms as PD risk factors, the authors noted.
However, “in addition to contributing to possible models of modifiable risk factors for PD, study results may also further inform algorithms designed to predict PD diagnoses in primary care,” they said. The study also highlights the need for more multivariable models to better identify PD risk factors and strategies for early identification of PD in primary care.
Several study coauthors received funding related to the study from Barts Charity, Health Data Research UK, the Department of Health and Social Care (England) and the devolved administrations, and leading medical research charities, as well as the National Institute for Health Research UCLH Biomedical Research Centre. Lead author Dr. Simonet and Dr. Hung had no financial conflicts to disclose. Dr. Patel disclosed support from the National Institute on Aging, the Mangurian-Fixel-McKnight Collaboration for Pilot Studies in Lewy Body Dementia, and the American Brain Foundation and the Mary E. Groff Charitable Trust. Dr. Chiu reported receiving grants from Mangurian-Fixel-McKnight Collaboration for Pilot Studies in Lewy Body Dementia and the Smallwood Foundation. Dr. Armstrong disclosed funding from the National Institute on Aging, the Florida Department of Health, the Lewy Body Dementia Association, the Alzheimer’s Therapeutic Research Institute/Alzheimer’s Clinical Trial Consortium, the Alzheimer’s Disease Cooperative Study as Data Safety Monitoring Board the Parkinson’s Foundation, and the American Academy of Neurology.