Pulmonary Function Tests in Idiopathic Inflammatory Myopathy: Association With Clinical Parameters in Children

Abstract

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.

A high level of serum neopterin is associated with rapidly progressive interstitial lung disease and reduced survival in dermatomyositis

“…Increased levels of neopterin have been reported in various clinical disorders, including several autoimmune diseases. The significant elevation of serum levels of neopterin in DM patients observed in our study are in agreement with previously published studies . In addition, we found that serum levels of neopterin correlated with disease activity in DM patients, as previously reported in juvenile myositis patients .…”

Consensus-based recommendations for the management of juvenile dermatomyositis

“… 62 The expert group determined that all children should have assessment of lung involvement at time of diagnosis by pulmonary function tests, including carbon monoxide (CO) diffusion capacity. 63 64 Further testing is necessary in those with an abnormal restrictive pattern, preferably in collaboration with a paediatric pulmonologist. The performance of pulmonary function tests can be difficult in very young children and can also be affected by general muscle weakness.…”

“… 63 There is insufficient evidence to advise on frequency of assessment during follow-up, but physicians should be aware of the long-term risk of lung involvement especially in those with a high myositis damage index (MDI) score 62 and a regular assessment of lung function may be prudent in patients that have positive anti-RNA synthetase antibodies. 64 …”

Pediatric Idiopathic Inflammatory Myopathies: An Update on Diagnostic and Treatment Strategies

“…In contrast, subclinical involvement of the respiratory muscles is rather frequent with a reduced total lung capacity in 26 to 78% of the patients. 14, 60,61 Dyspnea at exertion is found in up to 40% of the patients 14 and is more frequent in patients with polymyositis than in dermatomyositis or overlap syndromes. Restriction can be caused either by muscle weakness or by reduced motility of the thoracic wall.…”