Clinical characteristics and symptom progression of dermatomyositis subtypes: A retrospective analysis of a prospective database.

Background: Disease characteristics of classic dermatomyositis (DM) and clinically amyopathic DM (CADM) are well established, but there exists limited knowledge on the disease progression of these subtypes.

Objective: The objective of this study was to longitudinally track and characterize classic DM and CADM patients who experience changes in disease presentation.

Methods: We conducted a retrospective review of prospectively collected data on 269 DM patients from a longitudinal database.

Results: A total of 51% of the patients had classic DM and 49% had CADM. Forty percent of the classic DM patients became postmyopathic (PmDM). Median Cutaneous Dermatomyositis Disease Area and Severity Index activity (CDASI-A) score was lower in PmDM patients than in classic DM patients (13.0 vs 16.0), but 45% of the PmDM patients had CDASI-A scores > 14. Five percent of the CADM patients developed muscle involvement. Compared with CADM patients, those who developed muscle symptoms had milder skin disease before subtype conversion (median CDASI-A 12.0 vs 16.0) and at subtype conversion (median CDASI-A 9.0 vs 16.0).

Limitations: This was a retrospective study conducted at a single tertiary-care dermatology clinic.

Conclusions: Forty percent of the classic DM patients became PmDM. The majority continue with muscle disease, and many continue to have moderate/severe skin disease. CADM has a low risk of progressing to muscle disease, with the extent of skin disease as a potential predictive factor.