While patients with some types of parkinsonism have a shorter lifespan, those with Parkinson’s disease without cognitive impairment have a normal life expectancy, a Swedish population-based study suggests.
The study, “Early predictors of mortality in parkinsonism and Parkinson disease: A population-based study,” was published in the journal Neurology.
Studies have shown that life expectancy for Parkinson’s patients is reduced. However, conflicting data exists regarding the size of, and specific factors accounting for, the reduced survival compared with the general population.
Most studies of survival in Parkinson’s disease have been “hospital-based or have used register-based case-finding methods,” the researchers wrote. However, these designs may give rise to biased results.
In particular, cases of mild Parkinson’s disease may have been underrepresented, along with a lack of referral of older patients to hospital clinics.
“There are also few studies of the survival in unselected populations of patients with new-onset idiopathic parkinsonism (including atypical parkinsonism), rather than PD [Parkinson’s disease],” the researchers said.
Parkinsonism is a general term for neurological disorders that cause movement problems similar to those of Parkinson’s disease.
Parkinson’s dementia has also been associated with shorter survival, but mild cognitive impairment — an intermediate clinical stage not meeting the criteria for dementia — has not been studied in detail.
Aiming to address these gaps, the researchers assessed all-cause mortality and associated risk factors in a group of 182 Swedish patients with idiopathic parkinsonism, including 143 with Parkinson’s, 13 with multiple system atrophy (MSA), and 18 with progressive supranuclear palsy (PSP).
Patients were diagnosed from January 2004 through April 2009 in an area with 142,000 inhabitants. All underwent neurological, neuropsychological, neuroimaging, and laboratory tests, and received standard or advanced treatments during a long-term follow-up of up to 13.5 years. Memory and thinking skills, along with Parkinson’s symptoms, were assessed at the start of the study and at least once a year.
The team used a battery of validated tests, including the Unified Parkinson’s Disease Rating Scale (UPDRS) to assess both motor and non-motor symptoms; the modified Hoehn and Yahr Scale for disease progression; Mini-Mental State Examination (MMSE), which measures cognitive impairment; and the 39-item Parkinson’s Disease Questionnaire, a self-administered questionnaire that addresses aspects of functioning and well-being.
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Assuming a mean age of 71.7 years at baseline (the beginning of study) in idiopathic parkinsonism — meaning the disease is of unknown causes — the expected survival was 9.6 years for people with Parkinson’s and 6.1 years for people with PSP or MSA (atypical parkinsonism).
A total of 109 patients died during the study, including 54% of those with Parkinson’s, 89% of people with PSP, and 92% of patients with MSA. Of note, the lower survival observed in people with MSA or PSP — who had a mortality rate more than three times higher than the general population — was in line with previous studies.
In early Parkinson’s disease, mild cognitive impairment, freezing of gait, hyposmia (reduced sense of smell), decreased dopamine transporter activity in brain areas called caudate and putamen (implicated in motor control), and elevated white blood cells in the cerebrospinal fluid — the liquid surrounding the brain and spinal cord — (suggesting an activated immune response) were significantly associated with shorter survival.
Of note, the dopamine transporter is a protein responsible for the uptake of dopamine — a neurotransmitter present in low levels in Parkinson’s patients — back into neurons.
Importantly, the expected survival in Parkinson’s disease was 11.6 years without mild cognitive impairment and 8.2 years with mild cognitive impairment.
“Patients with Parkinson disease presenting with normal cognitive function seem to have a largely normal life expectancy,” the researchers wrote.
“The findings underscore the importance of an early [Parkinson’s]-MCI diagnosis,” they said.
Among the study’s limitations, the investigators mentioned that autopsies to confirm diagnosis were only conducted in five of the 109 people who died, and none of those with MSA. However, they believe that the long duration of follow-up minimized the risk of an incorrect diagnosis.