Background and Aims

Inclusion Body Myositis (IBM) is the most frequent myositis among the population over 50 years of age. Clinical and histological criteria enable the diagnosis of this disease. However, in some cases, a biological marker could be of interest like autoantibodies to cytosolic 5'-nucleotidase 1A (cN1A) or 43/44 kDa muscle protein (Mup 44).

The objective of this study was to evaluate retrospectively the clinical diagnostic value of these new antibodies.

Methods

Sera obtained from 44 patients with a definite (n=24) or suspected (n=20) IBM considering classical diagnostic criteria which were followed in clinical departments of different French centers during the last year were analyzed for anti-cN1A antibodies using a commercial ELISA technique (Euroimmun). Twenty five sera from patients with idiopathic inflammatory myopathy or myositis (9 polymyositis, dermatomyositis or anti-synthetase syndrome, 16 other myositis) were analyzed as controls.

Results

Seventeen sera out of 24 definite IBM and 4 out of 20 suspected IBM were found positive for anti-cN1A antibodies using the manufacturer’s cut-off value of 1 AU indicating a prevalence of 71% and 20% respectively whereas only 3 out of the 25 controls (12%) were positive.

Conclusions

In conclusion, despite a known prevalence of anti-cN1A antibodies in 20 to 26% of connective tissue diseases (mostly Sjögren’s Syndrome and lupus), their specificity in our study among myopathies is 88% when compared to similar idiopathic inflammatory myopathy or myositis diseases. Anti-cN1A antibodies could be thus useful for a better diagnosis of IBM and could be proposed as a biomarker of IBM.