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.