Fatty acid binding protein 3 is associated with skeletal muscle strength in polymyositis and dermatomyositis

Objective To determine serum levels and histopathological characteristics of fatty acid binding protein 3 ( FABP 3) in patients with polymyositis ( PM ) and dermatomyositis ( DM ), and to evaluate the correlation between the FABP 3 and muscle strength. Methods The study population included 24 subjects with PM / DM , 12 subjects with asymptomatic or minimally symptomatic hyper‐creatine kinase‐emia ( AMSH ), and 10 healthy control subjects. Muscle strength was measured by using the Manual Muscle Test ( MMT 8). Serum CK , myoglobin and FABP 3 levels were tested. Correlations between variables were studied by using Spearman's rank and partial correlation analysis methods. Immunohistochemical and double immunofluorescent stainings of FABP 3 were performed to investigate its distribution in skeletal muscle. Results PM / DM patients had significantly higher ( P < 0.05) serum FABP 3 levels (35.46 ± 38.45 ng/ mL ) than did AMSH patients (3.77 ± 1.21 ng/ mL ) and healthy control subjects (4.30 ± 3.18 ng/ mL ). MMT 8 scores correlated negatively with CK , myoglobin and FABP 3 levels. Partial correlation analysis was performed and showed that the correlation coefficients between MMT 8 score and serum CK , myoglobin and FABP 3 levels were −0.276 ( P > 0.05), −0.228 ( P > 0.05) and −0.927 ( P < 0.001), respectively. Immunohistochemical and double immunofluorescent staining showed that FABP 3 expression increased in the skeletal muscle of PM / DM patients and was mainly distributed in slow twitch muscle fibers. Conclusion Serum levels of FABP 3 in PM / DM patients were significantly increased and were mainly distributed in slow twitch muscle fibers, displaying a closer association with muscle weakness than did serum levels of CK and myoglobin. FABP 3 is likely to be a useful serum biomarker in PM / DM patients.