Pulmonary function tests in idiopathic inflammatory myopathy: Association with clinical parameters in children

Objective To determine the association of decreased lung function in children with idiopathic inflammatory myopathies (IIMs) with specific clinical parameters. Methods This study of 38 children ages 6-23 years diagnosed with definite/probable IIM evaluated the association of myositis-specific/-associated antibodies (MSAs/MAAs), duration of untreated disease at diagnosis, Disease Activity Score for muscle (DAS-M), muscle-derived enzymes (aldolase, lactate dehydrogenase [LDH], aspartate transaminase, and creatine phosphokinase [CPK]), neopterin and von Willebrand factor antigen, and the Childhood Myositis Assessment Scale (CMAS) scores with data from pulmonary function testing (PFT). Results Impaired PFTs were defined as total lung capacity (TLC) or diffusing capacity for carbon monoxide (DLCO) of <80% predicted. The PFTs documented that 37% of the children (14 of 38) had either decreased TLC or decreased DLCO; 5% (2 of 38) had both. Children with decreased TLC alone (7 [18%] of 38) were older both at the time of PFT and diagnosis, had anti-Jo-1 and anti-Scl-70 antibody, and had elevated levels of CPK and neopterin. Children with decreased DLCO alone (5 [13%] of 38) had a shorter duration of untreated disease at diagnosis, had higher DAS-M and total DAS, were positive for anti-Ro and anti-PL-12, had increased LDH, and had elevated levels of neopterin and aldolase, with low CMAS scores for items 1, 3, 10, 11, and 14. Conclusion Assessment of PFTs in children with IIMs should be considered, since more than one-third of patients were found to be impaired. The presence of MSAs/MAAs, an elevated serum neopterin level (mean ± SD 12.4 ± 9.6 nmoles/liter, normal value <10.5), older age at diagnosis, and shorter duration of untreated disease at diagnosis suggest the presence of potential lung pathology.