Polymyositis (and Dermatomyositis)

Introduction

• Chronic autoimmune disease. Peak incidence age 40-60; M:F = 1:2 
• Where skin is involved, the condition is known as dermatomyositis.

Clinical

• Main finding is a symmetrical muscle weakness and wasting involving the proximal muscles of the shoulder and pelvic girdles.
• Muscle pain and tenderness in 50%.
• Arthralgia and arthritis in 50%.
• Dysphagia in 50% due to oesophageal muscle involvement.
• Raynaulds may be present.
• In dermatomyositis, the rash is classically a heliotrope violet discolouration of the eyelids, forehead and cheeks. There may also be rash on hands and knees.

Diagnosis

• CK is frequently elevated.
• Muscle biopsies of muscle +/- skin.
• EMG studies: shows characteristic pattern.