The study with those findings, “Subjective cognitive decline and progression to dementia in Parkinson’s disease: a long-term follow-up study,” was published in Journal of Neurology.
Even during the early stages of disease, mild cognitive impairment can affect non-demented Parkinson’s patients, and is considered a risk factor for the development of dementia (PDD).
In fact, the prevalence of PDD increases as the disease progresses: from 28% after five years of evolution to 80% after 20 years of the disease.
Subjective cognitive decline — self-reported acquired difficulties with cognitive functioning — is common in the elderly and can be used as a predictor of dementia. In Alzheimer’s disease, subjective cognitive decline has been linked to disease-related tissue/molecular changes and a higher risk for dementia development. However, the predictive value of this type of cognitive status impairment has not been demonstrated yet in Parkinson’s disease.
Scientists from the University of La Laguna, Spain, investigated the neuropsychological profile of subjective cognitive decline in Parkinson’s disease and explored which components could better predict the development of PDD. The team also compared different screening tests to assess subjective cognitive complaints.
A total of 43 Parkinson’s patients and 20 healthy subjects were subjected to neuropsychological examination using a battery of cognitive tests. All patients were being medicated for Parkinson’s and were evaluated during their “on” state — when they are responding to medication and have reduced symptoms.
Subjective cognitive decline was diagnosed using two distinct approaches. A semi-structured interview in which the patient provided his/her subjective opinion on his/her attention, memory, spoken language, naming, written language, visuospatial skills and executive functions; diagnosis was considered when the patient had at least one cognitive complaint. Additionally, a subjective cognitive decline diagnosis also was established on the basis of the interview question concerning memory complaint.
Based on the results of the interview and on the MDS Task Force criteria, patients were diagnosed as having either subjective cognitive decline or mild cognitive impairment. Of the 43 patients, 13 (30.2%) were diagnosed with subjective cognitive decline, 22 (51.2%) with mild cognitive impairment and 8 (18.6%) had no subjective cognitive complaints. Difficulties in naming and memory were the most frequent cognitive complaints.
Based on memory complaints alone 10 patients (23.25%) were diagnosed with subjective cognitive decline. Interestingly, 10 of the 22 (45.45%) who had been diagnosed with mild cognitive impairment reported no memory complaints.
Mild cognitive impairment subjects performed poorer in the processing speed (the time it takes a person to do a mental task), executive functions (a set of mental skills that helps with organization and regulation), visuospatial skills, memory, and language domains, compared to the other groups.
There were no significant differences between healthy participants (controls) and Parkinson’s disease patients with subjective cognitive decline in any of the neuropsychological measures.
The team also assessed how many patients diagnosed with subjective cognitive decline progressed to dementia after a mean follow-up of 7.5 years. Fifty percent of mild cognitive impairment patients, 33.3% of individuals diagnosed with subjective cognitive decline, and 14.3% of patients without subjective cognitive complaints developed dementia, which was found to be associated with a poor performance in verbal and visuospatial memory and naming at the beginning of the study.
Additionally, both the language and memory domains were good predictors of dementia development.
“These results are highly relevant for future investigations and also for clinicians: the [subjective cognitive decline] assessment is frequently the first step of cognitive examination and can influence future decisions (e.g., to administer a screening test or a comprehensive neuropsychological assessment),” researchers wrote.
“Assessments that do not include procedures to adequately explore cognitive complaints may underestimate the proportion of [Parkinson’s-related subjective cognitive decline] and, therefore, [mild cognitive impairment] and thus misclassify patients as [Parkinson’s disease] with normal cognition, especially when brief cognitive examinations are chosen,” they concluded.