Interstitial lung disease in classic and skin-predominant dermatomyositis: a retrospective study with screening recommendations

Abstract

Objectives: (1) To determine the prevalence of interstitial lung disease (ILD) and isolated low diffusing capacity for carbon monoxide (DLCO) in a large cohort of outpatients with dermatomyositis. (2) To compare the pulmonary abnormalities of patients with classic dermatomyositis and those with skin-predominant dermatomyositis.

Design: Retrospective cohort study.

Setting: University hospital outpatient dermatology referral center. Patients Medical records of 91 outpatients with adult-onset dermatomyositis seen between May 26, 2006, and May 25, 2009, were reviewed.

Main outcome measures: Presence of ILD on thin-slice chest computed tomographic (CT) scans and DLCO.

Results: Of the 71 patients with dermatomyositis who had CT or DLCO data, 16 (23%; 95% confidence interval [CI], 13%-33%) had ILD as defined by CT results [corrected]. All patients with ILD had a reduced DLCO, and the ILD prevalence was not different between patients with skin-predominant dermatomyositis (10 of 35 [29% ]) and those with classic dermatomyositis (6 of 36 [17% ]) (P = .27). Eighteen of 71 patients with dermatomyositis (25%; 95% CI, 15%-36%) (7 of 35 [20%] with skin-predominant dermatomyositis; 11 of 36 [31%] with classic dermatomyositis; P = .41) had a low DLCO in the absence of CT findings showing ILD. The prevalence of malignant disease was higher in patients with classic dermatomyositis than in those with skin-predominant dermatomyositis (P = .02), and no patients with skin-predominant dermatomyositis had internal malignant disease.

Conclusions: Radiologic ILD and isolated DLCO reductions, which may signify early ILD or pulmonary hypertension, are common in dermatology outpatients with both classic and skin-predominant dermatomyositis. Because DLCO testing is both inexpensive and sensitive for pulmonary disease, it may be appropriate to screen all patients with dermatomyositis with serial DLCO measurements and base further testing on DLCO results.

Figure 1. Lung disease categories

JDM=juvenile dermatomyositis, ILD=interstitial lung disease, DLCO=diffusing capacity for carbon monoxide, CT=computed tomography (thin section).

Figure 2. Initial diffusing capacity for carbon monoxide (DLCO) categories and serial DLCO measurements

All values expressed as: No. patients (%). Serial DLCO defined as >1 DLCO measurement.

Figure 3. Initial screening and management of interstitial lung disease in dermatomyositis patients

HRCT=high resolution computed tomography (of the chest), ILD=interstitial lung disease, R/O=rule out, PFTs=pulmonary function tests, CBC=complete blood count, FEV1=forced expiratory volume in one second, FVC=forced vital capacity. *If spirometry shows obstructive disease (FEV1/FVC<70%) and the patient has a smoking history, note that reduced DLCO may be due to emphysema. However, this will not change management as HRCT is needed to rule out concomitant ILD.