Inflammatory myopathies

1. What is the clinical presentation of polymyositis?
2. What skin manifestations are seen in dermatomyositis?
3. What is the clinical presentation of inclusion body myositis?
4. What is seen on muscle biopsy in the inflammatory myopathies?
5. What is seen on EMG in polymyositis?

Answers:
1. Symmetrical proximal weakness, neck flexion weakness, myalgia, dysphagia, dysphonia, no facial or ocular weakness.
2. Periorbital violet rash and edema, Gottron's sign (red-purple patches over knuckles/knees).
3. Asymmetric, slowly progressive painless weakness both prox and distal.
4. Polymyositis bx shows necrosis of type I and II fibers and perifascicular atrophy. Inclusion body myositis bx shows rimmed or cytoplasmic/basophilic vacuoles, and eosinophilic inclusion bodies.
5. CMAP and SNAP normal. EMG shows abnormal activity (most common in paraspinals), early recruit, short duration small amp MUAPs.