Patients with primary progressive multiple sclerosis (PPMS) have more severe cognitive impairment than those with relapsing-remitting multiple sclerosis (RRMS), according to a German study that analyzed published data on the topic.
PPMS patients did especially poorly on verbal learning and verbal memory tests, said the study, which suggested that PPMS patients need disease management that specifically focuses on their cognitive difficulties, which do not necessarily correlate with the degree of overall disability.
The study, “Distinct cognitive impairments in different disease courses of multiple sclerosis – A systematic review and meta-analysis,” appeared in the journal Neuroscience & Biobehavioral Reviews, In it, researchers from the University Hospital Münster and the University of Münster in Germany gathered data from 47 previously published studies in an attempt to analyze potential differences in cognitive performance between patients with RRMS and PPMS.
These studies included 4,460 patients — 3,456 with RRMS and 1,004 with PPMS — and plenty of information about patient and disease features. This allowed researchers to perform a meta-analysis of pooled data from various studies, that is considered the highest level of scientific evidence.
Researchers noted that PPMS patients performed worse on cognitive tests, both when considering global scores and tests of specific cognitive domains. Yet both groups scored similarly in levels of anxiety, depression and fatigue.
Using statistical analyses, the research team found that differences in sex, education, disease duration, manual dexterity and fatigue could not explain the poorer test results among PPMS patients. On the other hand, PPMS patients were, on average, older than those with relapsing disease, and the team found that this difference accounted for poorer test results in cognitive tests of processing speed and working memory. Yet differences in other cognitive aspects also remained when researchers took age into account.
Differences in disability, measured by the Expanded Disability Status Scale (EDSS), could also not explain why PPMS patients performed worse on the cognitive tests.
A detailed look revealed that the largest differences between RRMS and PPMS patients were in verbal learning and verbal memory, along with the age-associated difference in processing speed.
Depression and anxiety also brought down processing speed, researchers said, even though the two groups did not differ in their levels of anxiety and depression.
The data shows that cognitive impairment in MS is not directly related to the course of the disease. Research may explain differences in other factors including genetics, the degree of brain tissue loss and medications.