[Interstitial lung diseases in polymyositis and dermatomyositis]

Interstitial lung disease is one of the most common respiratory manifestations in polymyositis and dermatomyositis. It still remains a severe complication of the disease, leading to death related to ventilatory insufficiency in 30-66% of patients.

Time onset of interstitial lung disease is variable, although interstitial lung disease onset precedes initial manifestations of polymyositis/dermatomyositis in roughly half of the patients. Moreover, clinical presentation of interstitial lung disease can be dichotomized, according to patients' pulmonary manifestations, into: 1) both acute and aggressive lung disease similar to Hamman-Rich syndrome; 2) slowly progressive lung disease; and 3) an asymptomatic pattern. The methods of choice adopted for early diagnosis of interstitial lung disease are high-resolution computed tomography scan and pulmonary function tests, which should be performed during both initial evaluation of polymyositis/dermatomyositis and follow-up. Because anti-JO1 antibody is considered to be a marker of interstitial lung disease in polymyositis/dermatomyositis, close pulmonary follow-up of anti-JO1-positive patients with polymyositis is therefore required for early detection of subclinical impairment. Furthermore, histological lung findings provide prognostic data; patients with bronchiolitis obliterans organizing pneumonia (BOOP) indeed appear to have a more favorable outcome than those with usual interstitial pneumonia or diffuse alveolar damage. Finally, as a guide to both the severity and progress of interstitial lung disease, the significance of other investigations, notably bronchoalveolar lavage, remains controversial.

Specific therapy of interstitial lung disease has not yet been clearly established in polymyositis/dermatomyositis patients. Corticosteroid therapy is considered the first line of therapy for polymyositis/dermatomyositis patients with interstitial lung disease. The association of cyclophosphamide and corticosteroids may be the most effective in patients with steroid-resistant interstitial lung disease. Early diagnosis and management of this disease is therefore of the utmost importance.