Dermatomyositis
Dermatomyositis
Dermatomyositis involves myositis plus skin changes; it has a female predominance; and the highest risk of malignancy of the inflammatory myopathies.
Skin Changes (Dermatomyositis)
Various skin changes can be found including:
- Heliotrope eyelid rash refers to inflammation of the face that manifests blue-violet (or violaceous) color (like a lilac, hence: heliotrope), which involves the eyelids (it includes varying degrees of periorbital edema).
- Butterfly-shaped, malar erythematous rash (note that malar refers to its site: the cheek and butterfly refers to its shape) crosses the nasolabial folds because this distinguishes it from the malar rash of systemic lupus erythematosus, which spares the nasolabial folds.
- Shawl sign: an erythematous, photosensitive rash across shoulder, neck, and back of the head, where a shawl would sit.
- Gottron's papules: small, swollen inflammatory lesions of red scaly areas over the knuckles.
- Calcinosis cutis, which is aberrant calcium depositions in the skin and subcutaneous tissues, which cause yellowish or white dermal lesions and stiffening with finger joint immobility.
- Dermatomyositis leads to the dystrophic calcinosis.
- Note that metastatic, iatrogenic, and idiopathic forms of calcinosis also exist.
Histopathology
Perifascicular atrophy refers to small, atrophic fibers, which is the hallmark pathological feature in DM.
- It's a specific but insensitive finding (only found in ~ 50% cases).
- There may be other findings as well, including perivascular inflammation: membrane attack complex deposition around small blood vessels, which is non-specific but common in DM.