Impact of sex, age at onset, and anti-cN1A antibodies on sporadic inclusion body myositis

Background: Inclusion body myositis (IBM) is a progressive myopathy occurring in patients over 45 years of age, with heterogeneous and variable clinical features. This study aimed to determine the influence of autoantibodies, gender, and age of onset on the clinical features of IBM.

Methods: Medical records and muscle histology findings of 570 participants with suspected IBM were reviewed. Various characteristics of patients who met the 2011 ENMC IBM diagnostic criteria were compared based on the presence of anti-cytosolic 5'-nucleotidase 1 A (cN1A) autoantibodies, gender, age of onset, and disease duration.

Results: Of the 353 patients who met the criteria, 41.6% were female. The mean age at onset was 64.6 ± 9.3 years, and the mean duration from onset to diagnosis was 5.7 ± 4.7 years. 196 of the 353 patients (55.5%) were positive for anti-cN1A autoantibodies and 157 were negative. Logistic regression showed that patients with anti-cN1A autoantibodies had a higher frequency of finger flexion weakness. Multiple regression showed that patients with later age of onset had shorter disease duration, lower BMI, and lower serum CK levels. Male patients had a higher frequency of onset with finger weakness and female patients had a lower BMI.

Conclusion: Autoantibodies, gender, age of onset, and disease duration may influence the clinical presentation of IBM, highlighting the need for a precision medicine approach that considers these factors along with the underlying mechanisms of the disease.