Interstitial lung disease (ILD) is a common complication of dermatomyositis (DM) with prevalence up to 65%, and is considered to be one of the determining factors of prognosis. Clinical amyopathic dermatomyositis (CADM), which is a special phenotype of DM, with characteristic cutaneous manifestations but no or only subclinical myopathy. Many studies, mainly from Asia, including ours, have demonstrated that these patients with CADM tend to develop a rapidly progressive ILD (RPILD) and have a poor response to conventional therapy, such as high-dose corticosteroids and immunosuppressants, leading to lethal outcome with a 6-month survival rate of less than 50%.

Pirfenidone, a new oral antifibrotic agent, has been approved for the treatment of idiopathic pulmonary fibrosis (IPF). Randomized controlled trials of pirfenidone in patients with IPF suggested that it could ameliorate pulmonary function decline and improve the progression-free survival. Its utility in connective tissue disease (CTD) related ILD has been implicated, but no evidence has yet demonstrated its efficacy. Therefore, the investigators conduct this study to evaluate the possible therapeutic effects of pirfenidone on RPILD associated with CADM.

Inclusion Criteria:

• Willingness of the subject to participate in the study, proven by signing the informed consent;
• All participants fulfilled the provisional diagnosis of CADM according to the modified Sontheimer's criteria.
• The course of ILD is longer than 3 months, but shorter than 6 months, presenting as increase in level of dyspnea, and worsening of fibrosis on pulmonary HRCT with >10% increase of HRCT score, and/or decrease in %FVC by >10% absolute value.

Exclusion Criteria:

• Participants who are unwilling to sign the inform consent;
• The course of participants ever treated with biologics including basiliximab, or malignancy-associated CADM or overlapped with other CTD, or with alanine transaminase more than 2 times the upper normal limits;
• Pregnancy or lactation.