Polymyositis/dermatomyositis

1. What muscles are affected?
*2. What are the five subtypes?
*3. What are the clinical features?
*4. What does muscle biopsy and EMG show?
5. What is the treatment?
*6. What are the features of juvenile dermatomyositis?

Answers:
1. Symmetrical weakness of proximal muscles, including shoulder and hip girdle, anterior neck flexors, pharyngeal involvement.
2. I: Primary idiopathic polymyositis (insidious). II: primary idiopathic dermatomyositis (acute). III: Polymyositis/dermatomyositis associated with malignancy. IV: Childhood dermatomyositis/polymyositis --> severe joint contractures. V: Associated with collagen vascular disease.
3. Symmetric proximal weakness which may involve respiratory muscles and cause dysphagia. Skin features include lilac heliotrope rash with periorbital edema and Gotton's papules.
4. Muscle biopsy shows perifascicular atrophy with necrosis of type I and II fibers. EMG shows myopathic cahnges (PSW, fibs, CRD), small short MUAPs with early recruitment.
5. Steroids, azathioprine, methotrexate. ROM, isometric exercises. Follow strength and serum enzymes.
6. Heliotrope rash is predominant, clumsiness, transient arthritis. Responds well to steroids.