1 | Symmetrical weakness of limb-girdle muscles and anterior neck flexors | ||
2 | Muscle biopsy evidence typical of myositis | ||
3 | Elevation of serum skeletal muscle enzymes, particularly CK | ||
4 | Typical EMG features of myositis | ||
5 | Typical DM rash, including heliotrope and Gottron’s papules | ||
For the diagnosis of PM | For the diagnosis of DM | ||
Definite | All of items 1–4 | Definite | Item 5 plus 3 of items 1–4 |
Probable | 3 of items 1–4 | Probable | Item 5 plus 2 of items 1–4 |
Possible | 2 of items 1–4 | Possible | Item 5 plus 1 of items 1–4 |
Exclusion criteria: congenital muscular dystrophies, central or peripheral neurological disease, infectious myositis, metabolic/endocrine myopathies and myasthenia gravis
CK = creatinine kinase; DM = dermatomyositis; EMG = electromyogram; PM = polymyositis