Table 1

Major muscle biopsy findings

Pathological featureDermatomyositisPolymyositisInclusion body myositis
Particularly important distinguishing features are emphasised either in bold or with ++.
Inflammatory infiltrates Perivascular EndomysialEndomysial
T cells > B cells++
B cells > T cells+
Partial invasion of fibres++++
Scattered necrotic fibres++
Perifascicular atrophy++
Zonal myofibrillar loss+
Rimmed vacuoles++
1° capillary loss+
15 nm filaments++
MHC-1 expression+++++