Background/Purpose:

Interstitial lung disease (ILD) frequently complicates Polymyositis (PM) and Dermatomyositis (DM) and accounts for significant morbidity and mortality in affected patients.  Patients with Myositis associated Interstitial Lung Disease (MA-ILD) are often refractory to conventional treatment which commonly includes the use of glucocorticoids with or without azathioprine, methotrexate or mycophenolate.  In recent years, tacrolimus has shown favorable outcomes in refractory MA-ILD.  Little is known about clinical variables that are associated with a response to treatment.  The aim of this study is to evaluate clinical predictors of response to conventional treatment and tacrolimus.

Methods:

This is a retrospective study of 54 patients with MA-ILD seen in Rheumatology and Pulmonology clinics at The University of Chicago.  Myositis was diagnosed based on Bohan and Peter criteria and ILD was diagnosed based on abnormalities on CT scan of chest. Chart review was performed and clinical variables were compared between the groups who responded versus failed to conventional treatment. All patients received glucocorticoids with at least one disease modifying agent (DMARDs such as azathioprine, methotrexate, mycophenolate mofetil) as conventional treatment for MA-ILD.  In those who failed conventional treatment, and were challenged with tacrolimus, clinical predictors to treatment were again evaluated. We strictly defined improvement in myositis (serial CK and objective muscle weakness) and ILD (serial pulmonary function tests and symptoms including cough and dyspnea). The response to tacrolimus was measured by observing the improvement in myositis, ILD and changes in the doses of glucocorticoids.

Results:

Our study included 30 patients with PM, 20 with DM, and 4 patients with clinically amyopathic dermatomyositis (CADM).  The mean age was 44.8 years (14.8 SD), and 48% of patients were African Americans.  23 out of 54 patients failed to respond to conventional treatment. Patients who had PM were more likely to respond to conventional treatment as compared to DM (p=0.017). There were 20 patients who received tacrolimus for treatment of refractory MA-ILD.  There was an improvement in ILD in 94% of patients and improvement in myositis in 75% of patients after the addition of tacrolimus.

The mean dose of prednisone at the time of initiation of tacrolimus was 33.6 +/- 4.3 mg.  After 3-6 months the mean dose of prednisone was 11.9 +/- 1.8 mg, p < 0.0001 (65% decrease) and was 7.32 +/- 1.7 mg, p < 0.0001 (78% decrease) by the end of 1 year. The mean dose of azathioprine at the time of initiation of tacrolimus was 88.15 +/- 16.7 mg.  By the end of 1 year the mean dose of azathioprine was 48.6 +/- 15.3 mg (p=0.003, 45% decrease).

Conclusion:

PM/DM/CADM is a group of rare, heterogeneous diseases and predicting their response to treatment remains challenging.  Patients with PM associated ILD were more likely to respond to conventional treatment than patients with DM associated ILD.  Tacrolimus is a favorable option in patients with refractory MA-ILD and was successful in decreasing the dose of baseline glucocorticoids and other DMARDS.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/myositis-associated-interstitial-lung-disease-clinical-predictors-of-failure-to-conventional-treatment-and-their-response-to-tacrolimus/