SNOWMASS, COLO. – Serial pulmonary function testing, including diffusion capacity, is routinely warranted – but all too often overlooked – in patients with skin-predominant dermatomyositis.

It’s not widely appreciated that patients with clinically amyopathic dermatomyositis and those with classic dermatomyositis are at similarly high risk for developing interstitial lung disease, Dr. Ruth Ann Vleugels observed at a symposium sponsored by the American College of Rheumatology.

"I often see patients with clinically amyopathic dermatomyositis who are assumed to have skin-limited disease and have never had pulmonary function tests. All these patients really should have serial pulmonary function tests with diffusion capacity studies. This is probably what’s most often forgotten, particularly in the evaluation of our amyopathic patients," declared Dr. Vleugels, a dermatologist who is director of the connective tissue disease clinic at Brigham and Women’s Hospital in Boston and codirector of the rheumatology-dermatology clinic at Children’s Hospital Boston.

She added that patients with amyopathic dermatomyositis, like those with classic dermatomyositis, are also at elevated risk for internal malignancy.

"The take-home message is, clinically amyopathic patients can have cancer and interstitial lung disease. So even though they don’t have muscle disease, we need to screen identically for malignancy and also work them up for interstitial lung disease," the dermatologist continued.

Dr. Vleugels highlighted a retrospective study by investigators at the University of Pennsylvania in Philadelphia that underscored the similarly high risk of interstitial lung disease (ILD) in patients with skin-predominant and classic dermatomyositis.

The study involved 71 patients with dermatomyositis who were screened for ILD via thin-slice chest CT scans and pulmonary function testing that included diffusing capacity for carbon monoxide (DLCO). In all, 35 patients had clinically amyopathic dermatomyositis (a condition formerly known as dermatomyositis sine myositis) and 36 had the classic form of the disease featuring muscle involvement.

The overall prevalence of ILD by CT scan was 23%. The pulmonary disease was present in 10 of 35 patients with clinically amyopathic dermatomyositis and in 6 of 36 subjects with the classic form of dermatomyositis featuring muscle involvement, rates that were not significantly different (Arch. Dermatol. 2010;146:729-38).

All dermatomyositis patients with ILD had a reduced DLCO. In addition, 7 of 35 with clinically amyopathic dermatomyositis and 11 of 36 with classic dermatomyositis had a low DLCO in the absence of CT evidence of ILD. The clinical implication of such findings remains unclear. It may be that an isolated low DLCO with a normal chest CT is an indication of early ILD, or perhaps pulmonary hypertension, but a larger study with longer follow-up will be required to learn whether, in fact, an isolated low DLCO in the setting of dermatomyositis predicts progression to restrictive lung disease.

Because all patients in this study with CT evidence of ILD also had a low DLCO, the investigators recommended that all dermatomyositis patients routinely undergo serial screening with pulmonary function tests. Those with a moderate or severe reduction in DLCO (that is, less than 61% of the predicted value) should undergo thin-slice CT and referral to a pulmonologist for further management.

Dermatomyositis patients with a mildly low DLCO (defined as 61%-75% of predicted) should also have a high-resolution chest CT, as well as echocardiography to rule out pulmonary hypertension. If these studies prove negative, close follow-up with serial pulmonary function tests as well as inquiry regarding the clinical symptoms of shortness of breath and cough is appropriate, according to the Penn investigators.

Dr. Vleugels endorsed this strategy. In addition, because the best available data suggest that 18%-32% of patients with dermatomyositis – whether classic or clinically amyopathic – have or will develop internal malignancy, she and her Boston colleagues routinely obtain CT scans of the chest, abdomen, and pelvis in all patients diagnosed with dermatomyositis. Women with dermatomyositis also undergo transvaginal pelvic ultrasound, which is a better screening tool for ovarian cancer. These studies are supplemented by age-appropriate GI endoscopy and stool occult blood tests. Women also get Pap smears and CA 125 measurement.

The cancer risk is greatest in the first 3 years following diagnosis of dermatomyositis, and remains high for at least 5 years.

The best data on the incidence of dermatomyositis in the United States, according to Dr. Vleugels, come from a population-based Mayo Clinic study conducted in Olmsted County, Minn. The overall incidence of dermatomyositis was 9.63 cases per 1 million population, with 21% of affected individuals having clinically amyopathic dermatomyositis. The internal malignancy rate wasn’t significantly different between patients with classic and clinically amyopathic dermatomyositis (Arch. Dermatol. 2010;146:26-30).

Dr. Vleugels reported having no financial conflicts.

Lung Disease Often Overlooked in Amyopathic Dermatomyositis