Table 1.

Characteristics of the study population including demographic, laboratory, and clinical data.

Demographic, Laboratory, and Clinical DataPM, n = 12DM, n = 10Possible DM Sine Dermatitis, n = 5Nonspecific Myositis, n = 14Not Myositis, n = 23IBM, n = 18All Patients*, n = 83
Median followup, yrs (range)5.0 (0.5–9.0)8.8 (3.5–12)6.5 (3.0–9.5)6.5 (0.5–12)8.0 (3.0–13)6.0 (2.5–10)7.0 (0.5–13)
Median age, yrs (range)62 (30–80)47 (7–77)57 (18–59)47 (31–83)52 (24–77)65 (48–81)60 (7–83)
EMG, M/N/0/−8/0/2/24/0/0/64/0/1/011/5/0/39/2/2/1111/5/0/348/12/5/25
Autoantibodies, tested/positive#9/510/95/512/1022/148/657/50
Creatine kinase above ref. value129514221780
Partial invasion as Amato/ENMC11120616**36
Perifascicular atrophy06504015
Therapy response, +/(+)/0/−††2/7/3/07/3/0/03/1/1/05/5/4/01/1/19/20/0/17/119/17/44/3
Neoplasia within 4 yrs2300005
Overlap syndrome532611027
  • * The group defined as immune-mediated necrotizing myopathy had only a single male patient; EMG showed myopathic findings, and his blood samples elevated creatine kinase and autoantibodies; he responded well to therapy.

  • ** In the biopsy of 1 patient the criteria of partial invasion according to Griggs classification were met, but the criteria of the Amato/ENMC classification were not. Another patient met all clinical and laboratory criteria of the Griggs classification (including amyloid deposits) except for partial invasion, and the diagnosis of possible IBM was chosen.

  • # Screening was performed for antinuclear antibody and extractable nuclear antigen.

  • M: myopathic findings; N: neuropathic findings; 0: normal findings; –: not performed.

  • †† +: complete or near-complete improvement of muscle strength; (+): incomplete but obvious improvement in muscle strength; 0: no or only slight improvement in muscle strength; –: no treatment was given. PM: polymyositis; DM: dermatomyositis; IBM: inclusion body myositis; EMG: electromyography; ENMC: European Neuromuscular Centre.