Table 4

Comparative features in selected immune myopathy syndromes

Myopathy syndromeClinical featuresPathological features
SRP antibodies Onset: autumn, acute, adultWeakness: severe, proximalSerum CK: very highSteroid responsiveMuscle fibres: degeneration, regeneration. Endomysial connective tissue: increased. Endomysial capillaries: diffuse pathology, reduced number, enlarged, MAC deposition. Inflammation: minimal
Jo-1 antibodies Onset: spring, adultWeakness: moderate, proximalFeatures: interstitial pneumonitis, Raynaud's, arthritisSerum CK: highSteroid responsiveMuscle fibres: perifascicular myopathy. Endomysial capillaries: normal. Perimysium: fragmentation. Inflammation: perimysial, macrophage
Paraneoplastic (necrotic) Onset: acute, older adultWeakness: severe, proximalSerum CK: very highSteroid responsiveMuscle fibres: regional necrosis, MAC deposition in sarcoplasm. Inflammation: within muscle fibres; macrophage
Dermatomyositis Onset age: child or adultWeakness: proximal > distalFeatures: rashSerum CK: highSteroid responsiveMuscle fibres: perifascicular atrophy. Endomysial connective tissue: normal. Endomysial capillaries: regional pathology, reduced number, enlarged, MAC deposition. Inflammation: perivascular, lymphocytic
Myositis + mitochondrial abnormalities Onset age: older adultWeakness: quadriceps, slowly progressiveSerum CK: normal or mildly highSteroid resistantMuscle fibres: focal invasion by inflammatory cells; cytochrome oxidase negative fibres. Inflammation: endomysial, lymphocytic