Table 4.

Muscle biopsy features, treatments, and duration of disease in anti-Jo1–positive patients diagnosed with DM and PM.

DM, n (%)PM, n (%)p
Perivascular inflammation9 (69.2)6 (85.7)0.6
Perifascicular atrophy8 (61.5)4 (57.1)1
Primary inflammation4 (30.8)4 (57.1)0.4
Mitochondrial dysfunction*2 (25.0)2 (16.7)1
Necrotizing myopathy2 (15.4)0 (0.0)0.5
Immunosuppression prior to biopsy8 (61.5)3 (42.9)0.6
Taking immunosuppression during biopsy6 (54.4)3 (42.9)1
Corticosteroids during biopsy4 (30.8)2 (28.6)1
Days from the onset of symptoms to the biopsy, median (Q1–Q3)725 (531–874)374 (37–435)0.1
  • * Because not all biopsies were stained with cytochrome oxidase, mitochondrial dysfunction could not be assessed in all cases. Fisher’s exact test and Wilcoxon rank-sum test p values are shown for the categorical and quantitative variables, respectively. DM: dermatomyositis; PM: polymyositis.