Seropositivity for NT5c1A antibody in sporadic inclusion body myositis predicts more severe motor, bulbar and respiratory involvement

Abstract

Objectives: To explore phenotypic differences between individuals with sporadic inclusion body myositis (sIBM) who are seropositive for the NT5c1A antibody compared with those who are seronegative.

Methods: Cross-sectional clinical, serological and functional analysis in 25 consecutive participants with sIBM.

Results: All participants met criteria for clinically defined or probable sIBM. 18 of 25 participants with sIBM (72%) were seropositive for the NT5c1A antibody. No differences between median age and duration of illness between the two groups were seen. Females have higher odds of being seropositive (OR=2.30). Participants with seropositive sIBM took significantly longer to get up and stand (p=0.012). There were no significant differences between the two groups in terms of distance covered on a 6 min walk. Seropositive participants were more likely to require assistive devices such as a walker or wheelchair for mobility (OR=23.00; p=0.007). A number of secondary (exploratory) outcomes were assessed. NT5c1A seropositive sIBM cases had lower total Medical Research Council (MRC) sum score and MRC sum score on the right (p=0.03 and 0.02, respectively). Participants with the NT5c1A antibody were significantly more likely to have symptoms of dysphagia (OR=10.67; p=0.03) and reduced forced vital capacity (p=0.005). Facial weakness occurred in 50% of seropositive participants while it was only seen in 14% of seronegative participants.

Conclusions: Even though the small sample size limits definite conclusions, our cross-sectional study showed seropositivity to the NT5c1A antibody is associated with greater motor and functional disability in sIBM. The study also suggests more prominent bulbar, facial and respiratory involvement in individuals positive for NT5c1A antibodies.

Keywords: INCL BODY MYOSITIS; MUSCLE DISEASE; MYOPATHY; RESPIRATORY MEDICINE; SWALLOWING.

Figure 1

Box-Whiskers plot of primary outcome measures. (A) Showing the differences in timed get up and stand test between the seropositive and seronegative sporadic inclusion body myositis (sIBM) groups. Seropositive participants took significantly longer to get up and stand from a standard chair compared with seronegative participants (median time was 15.2 s (n=17) in the seropositive participants versus 2.3 s in the seronegative participants (n=7; p=0.12)). (B) Showing the distance covered on a 6 min walk test between the two groups. Seropositive participants covered a median distance of 733 feet (n=17) while the seronegative participants covered a distance of 830 feet (n=7). There was no significant difference between the two groups.