The effect of cognitive impairment on the predictive value of multimorbidity for the increase in disability in the oldest old: the Leiden 85-plus Study

Objectives: this study investigates the predictive value of multimorbidity for the development of disability in the general population of very old people and the role of cognitive impairment in this association. Design: the Leiden 85-plus Study (1997-2004) is an observational prospective cohort study with 5 years of follow-up. Setting: general population of the city of Leiden, the Netherlands. Subjects: population based sample of 594 participants aged 85 years. Methods: disability in activities of daily living (ADL) was measured annually for 5 years with the Groningen Activity Restriction Scale (range 9-36, 9 = optimal). Multimorbidity is defined as the presence of two or more chronic diseases at age 85 years. Cognitive function was measured at baseline with the mini-mental state examination (MMSE). Results: at baseline participants with multimorbidity had higher ADL disability scores compared with those without [median 11 inter-quartile range (IQR 9-16) versus 9 (IQR 9-13) ADL points, Mann-Whitney U test P < 0.001]. Stratified into four MMSE groups, ADL disability increased over time in all groups, even in participants without multimorbidity (P trend < 0.001). Multimorbidity predicted accelerated increase in ADL disability in participants with MMSE of 28-30 points (n = 205, 0.67 points/year, P < 0.001), but not in participants with lower MMSE scores (all P > 0.100). Conclusion: the predictive value of multimorbidity for the increase in ADL disability varies with cognitive function in very old people. In very old people with good cognitive function, multimorbidity predicts accelerated increase in ADL disability. This relation is absent in very old people with cognitive impairment.