Background: The current diagnostic criteria for dermatomyositis (DM) exclude patients without muscle involvement. As a result there is a paucity of research related to the complete spectrum of the disease.
Objective: The goal of this study was to evaluate differences in the clinical manifestations of DM seen by dermatology relative to rheumatology. We hypothesized that patients with minimal (hypomyopathic) or no (amyopathic) muscle disease would more likely be seen in dermatology, whereas those with more severe (classic) muscle disease would be seen in rheumatology.
Methods: We performed a retrospective chart review of patients with DM seen by our dermatology and rheumatology departments to classify spectrum, presentation, and complications. Patients seen between July 1, 2003, and June 30, 2006, were identified by Current Procedural Terminology billing code 710.3. Patients with mixed connective tissue diseases or miscoded DM were excluded.
Results: In all, 131 (65%) patients seen in dermatology, 58 (29%) in rheumatology, and 13 (6%) in both departments were identified. In all, 83 (69%) patients seen in dermatology, 27 (23%) in rheumatology, and 10 (8%) in both departments met criteria for inclusion in the study. The number of patients seen in rheumatology given the classification of classic DM (CDM) (24 of 27 [89%]), hypomyopathic DM (2 of 27 [7%]), and amyopathic DM (ADM) (1 of 27 [4%]) differed significantly from dermatology, where CDM comprised 27 of 83 (33%), hypomyopathic DM comprised 23 of 83 (28%), and ADM comprised 33 of 83 (40%) of the population, respectively (P < .001). Sex, ethnicity, and rates of interstitial lung disease differed between departments. There was no difference in the rates of interstitial lung disease between CDM and ADM (P = .30). The degree of muscle involvement did not correlate with the rates of DM-associated malignancy (P = .57). Few patients with ADM had muscle biopsy (n = 1) or electromyography (n = 7) testing. Positive anti-Jo-1 was seen in 2 of 96 patients (2%; one CDM and one ADM, both with interstitial lung disease), reflecting an overall low prevalence of this autoantibody, or a potential problem with the laboratory assay.
Limitations: Patients reflect the population in only one institution and, thus, the results may not be generalizable to other settings or referral centers. Because this is a retrospective chart review, results are limited by missing data and nonstandardized physical examinations and laboratory data across patients and physicians.
Conclusions: There is a clear difference in DM presentation to dermatology and rheumatology by degree of myositis-complicated disease.