Immune-Mediated Polymyositis, Dermatomyositis, Reactive Arthritis, and Enthesitis

Polymyositis is a systemic connective-tissue disease with inflammatory and degenerative muscle changes. Dermatomyositis usually involves both skin and muscle. The resulting weakness is symmetric, principally affects the limb girdles, and may be accompanied by muscle atrophy.

• Heliotrope rash: eyelid involvement with edema
• Gottron’s rash: erythema of the knuckles with a scaly eruption
• V sign: rash on the neck and anterior chest
• Shawl sign: rash across the back and shoulder

Reactive arthritis, also called Reiter’s syndrome, is a postinfectious seronegative spondyloarthropathy. Its pattern associates arthritis with nonbacterial urethritis or cervicitis, conjunctivitis, and mucocutaneous lesions.

Small, painless, superficial ulcers commonly affect the oral mucosa, tongue, and glans penis; glans involvement is called balanitis circinata. Hyperkeratotic lesions may develop on the palms, soles, and around the nails; this is keratoderma blennorrhagica.

Females are affected more commonly. The characteristic clinical pairing is rash with muscle weakness. Weakness is proximal, and loss of fine motor movements may occur.

Dermatomyositis can be associated with malignancy in 10–20% of cases.

Arthritis is usually the second or third feature and ranges from mild to severe. Joint involvement is generally asymmetric and polyarticular, affecting the large joints of the lower extremities and the toes. Back pain may occur, usually with more severe disease.

Cardiovascular involvement is rare and may include aortitis, aortic insufficiency, and conduction defects.

Serum muscle enzymes are usually elevated, especially transaminases, creatine kinase (CK), and aldolase. CK is described as the most sensitive and useful enzyme and as a reliable biochemical marker of myositis in dermatomyositis.

Enthesopathy is inflammation where a tendon inserts into bone. It is common in reactive arthritis and other seronegative arthritides. Examples include plantar fasciitis, digital periostitis, and Achilles tendinitis.