Bohan and Peter defined criteria for the diagnosis of myositis and polymyositis. Exclusion of mimicing conditions is important for accurate diagnosis. The authors are from the UCLA School of Medicine.
Criteria:
(1) symmetrical proximal muscle weakness, with or without dysphagia and respiratory muscle weakness. developing over weeks or months
(2) elevation of serum enzymes (CK, aldolase, LDH, transaminases)
(3) electromyographic triad of
(3a) small amplitude, short duration polyphasic motor unit potentials
(3b) fibrillations, positive sharp waves, increased insertional irritability
(3c) spontaneous, bizarre high frequency (complex repetitive) discharges
(4) muscle biopsy abnormalities: skeletal muscle degeneration, regeneration, necrosis, and phagocytosis, with an interstitial mononuclear cell infiltrate
(5) rash of dermatomyositis
(5a) heliotrope rash
(5b) Gottron's papules or sign, involving the finger joints, knees, elbows, and/or medial malleoli
(5c) erythematous and/or poikilodermatous rash
Conditions that must be excluded (see Table 5, page 1264, Targoff):
(1) evidence of peripheral or central nervous system involvement
(2) sarcoidosis
(3) active infection involving muscle
(4) drugs or toxins associated with myopathy
(5) rhabdomyolysis of known cause
(6) metabolic disorders of muscle
(7) presence of an endocrinopathy
(8) muscular dystrophy
(9) giant cell arteritis and other forms of vasculitis
(10) myasthenia gravis
(11) rubella vaccination
(12) atheromatous or carcinomatous microembolization
(13) Guillain-Barre syndrome
(14) malnutrition
Interpretation:
• minimum number of criteria present: 0
• maximum number of criteria present: 5 (with the skin rash)
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Diagnosis
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Polymyositis
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Dermatomyositis
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definite
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4
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3 or 4 + rash
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probable
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3
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2 + rash
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possible
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2
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1 + rash
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