The subjective cognitive decline in Parkinson's disease could predict the development of dementia. Therefore, adequate cognitive screening tests could help provide an accurate diagnosis and prognosis.
The study with these results, "Subjective cognitive decline and progression to dementia in Parkinson's disease: a long-term follow-up study" was published in Journal of Neurology.
Even in the early stages of the disease, mild cognitive impairment can affect patients without Parkinson's disease and is considered a risk factor for the development of dementia (PDD).
In fact, the prevalence of PDD increases with the progression of the disease: from 28% after five years of evolution to 80% after 20 years of illness.
The subjective cognitive decline – acquired self-reported 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 tissue / molecular changes related to the disease and to a higher risk of dementia development. However, the predictive value of this type of impairment of cognitive status has not yet been demonstrated in Parkinson's disease.
Scientists from the University of La Laguna, Spain, studied the neuropsychological profile of subjective cognitive decline in Parkinson's disease and explored which components could better predict PDD development. The team also compared several screening tests to assess subjective cognitive complaints.
A total of 43 patients with Parkinson's and 20 healthy subjects underwent neuropsychological examination using a battery of cognitive tests. All patients were treated for Parkinson's disease and were evaluated during their "on" status – when they respond to medication and have reduced symptoms.
The subjective cognitive decline was diagnosed using two distinct approaches. A semi-structured interview in which the patient provided his subjective opinion about his attention, memory, spoken language, naming, written language, visuospatial skills and executive functions; the diagnosis was made when the patient had at least one cognitive disorder. Furthermore, a subjective diagnosis of cognitive decline was established based on the interview question regarding memory disturbance.
For a slight cognitive diagnosis of damage, investigators followed the criteria proposed by the Movement Disorder Society (MDS)
Based on the results of the interview and the MDS Task Force criteria, patients were diagnosed with subjective cognitive impairment 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 impairment. The difficulties in naming and memory were the most frequent cognitive complaints.
Based on memory disorders, only 10 patients (23.25%) were diagnosed with subjective cognitive decline. Interestingly, 10 of the 22 (45.45%) who were diagnosed with mild cognitive impairment reported no memory complaints.
Subjects with mild cognitive impairment have weaker performance in processing speed (the time taken by a person to perform a mental task), executive functions (a set of mental abilities that help with organization and regulation), skills visuospatial, memory and domains of language, compared to other groups.
There were no significant differences between healthy patients (controls) and patients with Parkinson's disease 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 7.5-year follow-up. 50% of patients with mild cognitive impairment, 33.3% of subjects diagnosed with subjective cognitive decline and 14.3% of patients without subjective cognitive disorders developed dementia, which was associated with poor performance in verbal memory and visuospatial and in the denomination at the beginning of the study.
Furthermore, both language and memory domains were good predictors of dementia development.
"These results are very important for future investigations and also for doctors: the [subjective cognitive decline] assessment is often the first step of cognitive examination and can influence future decisions (eg, to administer a screening test or a complete neuropsychological evaluation), "the researchers wrote.
"Evaluations that do not include procedures to adequately explore cognitive disorders can underestimate the proportion of [Parkinson’s-related subjective cognitive decline] and therefore, [mild cognitive impairment] and then incorrectly classify patients as [Parkinson’s disease] with normal cognition, especially when short cognitive exams are chosen, "they concluded.