Diagnosing muscle disease in a cohort of classic dermatomyositis patients seen at a rheumatologic dermatology outpatient clinic.

Existing criteria include muscle biopsies to improve the probability of capturing dermatomyositis (DM), but not much is known whether less invasive diagnostic procedures may be just as useful.We aim to determine if skin biopsy, electromyography (EMG), or magnetic resonance imaging (MRI) of the involved muscle can be done in lieu of muscle biopsies.Two hundered and seventy-five patients were reviewed to investigate the presence of cutaneous and muscle disease, their timing in relation to diagnosis, and results of skin biopsies, muscle biopsies, MRIs, and EMGs.Of the cases who had findings consistent with DM on muscle biopsy, 65% were in agreement with diagnostic features on EMG or MRI. Results of skin and muscle biopsies supported DM in 67% of patients who underwent both procedures.A limited number of patients had muscle biopsies.In the presence of DM-specific skin findings, less invasive procedures may be sufficient to diagnose DM, and guide its management.

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Authors: S Ahmed, J Concha, S Chakka, R L Krain, D Zamalin, G Foulke, V P Werth