A cross-sectional study of memory and executive functions in patients with sporadic inclusion body myositis.

INTRODUCTION Sporadic inclusion body myositis (IBM) is a degenerative and inflammatory acquired myopathy characterised by muscle deposition of various proteins typically associated with Alzheimer's disease and other neurodegenerative diseases. While cognitive impairment is not noted as a clinical feature of IBM, evidence is lacking. We aimed to investigate whether cognitive performance of patients with IBM differs from population norms, focussing on cognitive domains affected in early Alzheimer's disease (memory, executive function), and to test whether disease duration and the level of disability of IBM are associated with cognitive function. METHODS Twenty-four patients with IBM (mean [SD] age 62.0 [7.2] years; disease duration 9.6 [4.8] years) were assessed cross-sectionally on neuropsychological tests covering multiple cognitive domains, including the Preclinical Alzheimer Cognitive Composite (PACC). Performance was compared to published normative data adjusted for age, sex and education (National Alzheimer's Coordinating Center; N = 3268). Associations were examined between PACC score, disease duration and level of disability (assessed using the IBM Functional Rating Scale [IBMFRS]). RESULTS Across all cognitive tests, group performance was within ±1SD of the normative mean. There was no evidence of associations between PACC score and either disease duration (ρ = -0.04, p = 0.87) or IBMFRS total score (ρ = 0.14, p = 0.52). DISCUSSION Memory and executive function in patients with IBM did not differ from normative data, and we observed no evidence of associations between the cognitive composite and disease duration or level of disability. This addresses a question frequently asked by patients, and will be of value for clinicians and patients alike. This article is protected by copyright. All rights reserved.