dermatomyositis

introduction

a connective-tissue disease related to polymyositis (PM) that is characterized by inflammation of the muscles and the skin
may also affect the joints, the esophagus, the lungs, and, less commonly, the heart
~100-200 cases per million
more common in women
juvenile form is similar
is often associated with Anti-Jo1 antibodies, Anti-signal recognition particle antibodies (anti-SRP) and Anti-Mi-2 antibodies
often associated with underlying cancers, in particular, ovarian tumours, lung cancer, and pancreatic cancer

presents as a proximal symmetrical muscle weakness with vasculitis affecting the skin, muscles and internal organs
many find it hard to raise their arms to comb their hair or walk up the stairs due to the proximal muscle weakness
other possible features:
- calcinosis can occur in the skin, joints and tissues
- Gottron lesions
  - scaly erythematous eruptions or red patches overlying the knuckles, elbows, and knees are a characteristic feature
- periungual telangiectasiae
- heliotropic (purple) rash over the upper eyelids
- Shawl (or V-) sign is a diffuse, flat, erythematous lesion over the back and shoulders or in a “V” over the posterior neck and back or neck and upper chest, which worsens with UV light.
  - erythroderma is not a flat, erythematous lesion similar to the shawl sign but located in other areas, such as the malar region and the forehead.
- mechanic's hands (also in PM)
  - rough, cracked skin at the tips and lateral aspects of the fingers forming irregular dirty-appearing lines that resemble those seen in a labourer
- psoriaform changes in the scalp
- centripetal flagellate erythema comprises linear, violaceous streaks on the trunk (possibly caused by itching pruritic skin)
- calcinosis cutis (deposition of calcium in the skin) is usually seen in juvenile dermatomyositis, not adult dermatomyositis
- dysphagia occurs in a third
- priapism
- dystrophic calcifications in the muscles on XR

raised creatinine kinase (CK) and erythrocyte sedimentation rate (ESR)
muscle biopsy:
- mixed B- and T-cell perivascular inflammatory infiltrate
- perifascicular muscle fiber atrophy