Is the Impact of Somatic Diseases on Cognitive Functions Clinically Important?

Background/Objectives: Somatic multimorbidity and mental disorders are associated with impaired cognitive functions, but the clinical importance has rarely been considered. This study evaluated the clinical importance of the associations between cognitive functions and somatic comorbidity. Methods: This cross-sectional study used data from the national research and quality registry “The Norwegian Registry of Persons Assessed for Cognitive Symptoms” (NorCog). Out of 9525 persons in the registry, 3794 (males/females 1789 (47%)/2005 (53%) with a mean age of 74.8 (SD 8.6) years) with mild cognitive impairment (MCI) and dementia had complete registration of age, sex, BMI, years of education, depression (Cornell scale), and somatic diseases and were included in the study. Cognitive functions were assessed with a Norwegian version of Mini-Mental State Examination (MMSE-NR3), Word List Memory Test (WLMT) Immediate and Delayed recall, and Trail Making Test (TMT) A and B. Changes were compared with established limits for minimal clinically important differences (MCID). Twenty-six somatic disorders were registered and grouped into cardiovascular disease, cerebrovascular disease, neurological disease, and metabolic disease. All associations between cognitive functions and somatic diseases were studied using linear regression with the cognitive test scores as dependent variables and somatic diseases as predictors Results: The number of comorbidities and cerebrovascular disease was statistically significantly associated with improved MMSE-NR3 and WLMT Immediate and Delayed test scores. The changes in scores were not clinically important. Neurological disease was associated with improved WLMT Delayed scores and impaired TMT-A scores, but neither change was clinically important. Conclusions: There were statistically significant associations between somatic morbidity and cognitive functions, but none were clinically important. Referral to MCID in addition to statistical differences deserves increased attention in clinical studies.