Mixed Connective Tissue Disease
MCTD is characterized by having features of multiple connective tissue disorders, but primarily SLE, polymyositis/dermatomyositis, and scleroderma. Symptoms can evolve over time and do not present in a specific order [112]. Criteria for diagnosis include 1) Raynaud’s phenomenon 2) detectable anti-RNP antibodies 3) one additional sign or symptom of SLE, polymyositis/dermatomyositis or SSc [113, 114].
MCTD can be accompanied by any of the pulmonary manifestations of SLE, JDM, or SSc, most often, pleural effusions, pulmonary hypertension, and ILD. The prevalence of overall pulmonary involvement in children is unknown, but most adults with MCTD have pulmonary involvement [115-119], which increases the risk for mortality.
The disease course of ILD in pediatric MCTD is not well defined. In a prior cross-sectional study of 52 pediatric MCTD patients followed for a mean of 16 years, ILD was diagnosed in 27%. On PFTs, patients with ILD had lower FVC and TLC than controls. Notably, in this study, while FVC declined overtime, CT findings of ILD did not worsen [33]. A second long-term follow up study of pediatric MCTD (n = 34) hints at a potentially progressive nature of ILD in MCTD — at initial presentation, 22% of patients had restrictive lung disease, 21% had reduced DLCO and 14% had pulmonary fibrosis on chest CT, increased to 64% with restrictive lung disease, 58% with reductions in DLCO and 100% with fibrosis at long term follow up. 6% of patients in this series had pulmonary hypertension [120]. In addition to fibrosis, chest CT findings previously reported in MCTD include reticulations, ground glass opacities, interlobular septal thickening, airspace consolidations, and/or traction bronchiectasis [32].
Treatment pediatric MCTD patients is directed at specific complications that emerge and overlap with treatment paradigms used in SLE, polymyositis/dermatomyositis and SSc.