MUSCLE WEAKNESS AFFECTS FUNCTION DIFFERENTLY IN MALES AND FEMALES IN INCLUSION BODY MYOSITIS: PROVIDING RESULTS FOR FOCUSED CLINICAL CARE AND CLINICAL TRIAL DESIGN

Abstract Background Sporadic inclusion body myositis (IBM) is a muscle wasting disorder usually affecting those aged over 50 years, characterised by slowly progressive weakness of the distal upper limbs and proximal lower limbs. Particular weakness of pinch, knee extension and ankle dorsiflexion result in functional decline and disability. Weakness-associated functional decline differences between genders has not previously been investigated. This study aimed to investigate for differences of functional decline in men and women with IBM. Methods A cohort of verified adult IBM patients were followed at a single specialist neuromuscular clinic (Royal Victoria Infirmary, Newcastle-upon-Tyne, UK) between 2004-15, with data collected at each clinic visit. Strength of 11 movements was measured via dynamometry at each clinic visit. Patient-reported function was measured via the Neuromuscular Symptom Score (NSS). Generalised linear modelling, adjusted for disease duration, was carried out to identify associations between strength and function (NSS). Pinch, knee extension and ankle dorsiflexion strength measurements were analysed. Modelling was carried out separately for male and female cohorts. Results Data of 75 participants (47% female) was analysed. A total of 591 measurements were taken. Median age at time of IBM diagnosis was 68.8 years. Median baseline NSS score was 45 (IQR 37, 54) for the male cohort and 40 (IQR 29, 45) for the female cohort. The median disease duration of the study cohort was 2.6 years. Reduced function (NSS) was significantly associated with reduced pinch, knee extension and ankle dorsiflexion strength in the male cohort only (Table 1). No significant associations were observed in the female cohort. Conclusion This is the first study to demonstrate that the progression of weakness, in the characteristic muscle groups affected in IBM, impacts on function differently in men and women. These results illustrate the importance of functional assessment in patients with IBM and the importance of focused physiotherapy upon function-dependent muscle groups. Further, potential gender-based differences of weakness-related function in IBM should be considered when designing clinical trials. Disclosures J. Williams None. A. Oldroyd None. J. Lilleker None. H. Chinoy None. J. Miller None.