1. Symmetric progressive muscle weakness affecting the muscles of the shoulder and hip

2. Histologic findings typical of myositis (see text)

3. Increased plasma creatine kinase levels

4. Electromyographic features of an irritative myopathy (active changes and myopathic potentials)

5. Typical cutaneous manifestations: Gottron sign, heliotrope rash, or rash on the anterior chest and shoulders

Diagnosis

Definite

Probable

Possible

Number of symptoms

PM

4

3

2

DM

3 or 4

2

1

Plus typical cutaneous manifestations