Background/Purpose: A few cases of the concomitant development of interstitial pneumonia associated with dermatomyositis (DM-IP) and rheumatoid arthritis (RA) have been reported mainly in Asia, but the details are still unclear. The possible induction of dermatomyositis (DM) and polymyositis by TNF inhibitor has been pointed out, but no conclusion has been reached. We investigated the clinical features of DM-IP which concomitantly developed during the treatment of RA.

Methods: The subjects were 14 consecutive patients with DM-IP complicating RA treated at our department between November 2005 and October 2015, and the clinical features, such as patient background, clinical symptoms, examinations, treatment, and outcome, were retrospectively investigated. RA was diagnosed using the 1987 Revised ACR classification criteria and 2010 ACR/EULAR classification criteria, and DM was diagnosed using the criteria of Bohan and Peter. For the classification of clinically amyopathic dermatomyositis (CADM), the criteria of Sontheimer and Gerami were used. IP was diagnosed using chest HRCT, and the pattern was classified following the 2013 Update of the International Multidisciplinary Classification of the Idiopathic Interstitial Pneumonias.

Results: The median (IQR) onset age of DM-IP was 62.5 years old (54-68.5). All patients were female, and 4 were smokers (29%). The duration of RA illness until the development of DM-IP was 1,095 days (577-1,580). DM-IP newly developed during RA treatment in 5 patients at our department and the incidence was 0.57%. Nine patients were transferred for IP treatment from other hospitals. ACPA was >100, 15-100, and <15 U/mL at the time of RA diagnosis in 7 (54%), 3 (23%), and 3 (23%), respectively, RF was 58 IU/mL (33-149), and radiologic damage was noted in 11 (79%). RA was treated with MTX in 6 (42.9%), PSL in 6 (42.9%), BUC in 2 (14.3%), TAC in one (7.1%), biologics in 4 (28.6%) (ETN in 3 and GLM in 1), and others in 4 (28.6%). IP exacerbated within one month in 3 (21.4%) and 1-3 months in 4 (28.6%), and a slow course taking 3 months or longer was observed in 7 (50%). At the onset time of DM-IP (at the time of diagnosis), KL-6 was 769 U/mL (368-1,215), aldolase was 7.2 U/L (5.8-11.2), CK was 83 U/L (40-331), and ferritin was 119 (91-253) ng/mL. On chest HRCT, the NSIP and OP patterns were noted in 7 each (50%), and no honeycomb lung was seen. In all patients, dorsal lower lung field-dominant shadows newly appeared. On imaging before the development, the NSIP pattern was observed in 4 (28.6%), but no existing feature of IP was noted in 10 (71.4%). DM-IP was treated with PSL in all patients, and IVCY, CsA, and TAC were administered to 3, 9, and 3 patients, respectively. Cyclosporin was administered at 4 mg/kg in all treated cases, and cyclophosphamide was concomitantly administered to severe cases. Regarding the outcome, remission was achieved in all patients without recurrence.

Conclusion:  DM-IP frequently developed concomitantly with RA in females with a high ACPA titer. Various DMARDs were used in previous RA treatment, but TNF inhibitor was used as a biological product in all cases. When NSIP and OP appear dominantly in the lower lung field during RA treatment, the concomitant development of DM-IP should be suspected.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/concomitant-development-of-interstitial-pneumonia-associated-with-dermatomyositis-and-rheumatoid-arthritis/