Dermatologic manifestations of dermatomyositis
Heliotrope (lilac-colored) rash (<50% of DM patients): purple to erythematous rash affecting the eyelids, malar region, forehead, and nasolabial folds. Note that the eyelids and nasolabial folds are typically spared in the rash of SLE.
Gottron’s papules (60%–80% of DM patients): purple to erythematous flat or raised lesions over the dorsal surface of metacarpals and interphalangeal regions of the fingers (i.e., knuckles). Can also occur over extensor surfaces of the wrists, elbows, and knees.
V-sign rash: confluent erythematous rash over the anterior chest and neck.
Shawl-sign rash: erythematous rash over the shoulders and proximal arms.
Holster-sign rash: erythematous rash over the lateral aspect of proximal thighs.
Nailfold abnormalities: periungual erythema, cuticular overgrowth, dilated capillary loops (: Raynaud’s Phenomenon).
Photosensitivity: common with other rashes mentioned earlier.
Subcutaneous calcification: seen most commonly in JDM; can be very extensive.
DM mimics: these can include cutaneous manifestations of trichinosis, allergic contact dermatitis, and drug reactions (hydroxyurea most common, penicillamine, diclofenac, anti-tumor necrosis factor agents).
Pearl: A patient with proximal muscle weakness, elevated muscle enzymes, and the characteristic rash of DM rarely needs a muscle biopsy to confirm the diagnosis.