Inflammatory Myopathies

Original Editor - Lucinda hampton Top Contributors - Lucinda hampton, Rachael Lowe, Kim Jackson and Tony Lowe


The idiopathic inflammatory myopathies (IIMs) are a group of rare, acquired disorders with primary features of muscle weakness and inflammatory lesions identified in skeletal muscle specimens.The three most mentioned of the idiopathic, immune-mediated varieties of IIMs are: dermatomyositis (DM), polymyositis (PM) and inclusion body myositis (IBM)[1].

Patients typically present with sub-acute to chronic onset of proximal weakness manifested by difficulty with rising from a chair, climbing stairs, lifting objects, and combing hair. They are uniquely identified by their clinical presentation consisting of muscular and extramuscular manifestations. Laboratory investigations, including increased serum creatine kinase (CK) and myositis specific antibodies (MSA) may help in differentiating clinical phenotype and to confirm the diagnosis. However, muscle biopsy remains the gold standard for diagnosis. These disorders are potentially treatable with proper diagnosis and initiation of therapy. Goals of treatment are to eliminate inflammation, restore muscle performance, reduce morbidity, and improve quality of life.[2]

This video gives a brief summary of the condition(s).

Pathological Process, Incidence and Prevelance

The etiopathogenesis of these diseases is not fully understood. An autoimmune etiology of the IIMs is supported by the presence of serum autoantibodies, complement deposition in muscle tissue (in DM patients), lymphocyte-mediated cytotoxicity, and general clinical improvement in response to immunosuppression. Environmental triggers and genetic susceptibility are likely also involved with clear HLA gene associations and geographic case clusters. For example, HLA gene DRB1*0301 allele is associated with PM and IBM.[1]

  • The prevalence and incidence of these muscle diseases varies and is dependent on definitions and diagnostic criteria.
  • Overall annual incidence rates for the IIMs vary from 2.18 to 7.7 per million
  • Incidence rates also change with age and gender. There is a bimodal age distribution with peaks at age <15 and another between ages 45–54. There is a slight female predominance (F:M = 1.5:1.0)
  • IBM is the most common subtype in men over the age of 50 .
  • Under age 50, DM is more common than PM
  • Incidence seems to be increasing, but this may reflect changes in disease awareness, medical billing codes, medical record technology, and more sensitive diagnostic tools.

Clinical Presentation

Patients typically present with sub-acute to chronic onset of proximal weakness manifested by:
Five Times Sit to Stand Test.jpg
  • Difficulty with rising from a chair
  • Climbing stairs
  • Lifting objects
  • Combing hair

They are uniquely identified by their clinical presentation consisting of muscular and extramuscular manifestations.[2]

Diagnostic Procedures

Over the course of time, several different criteria have emerged to classify the IIM. Bohan and Peter criteria are the earliest and still widely used[2]

Diagnostic criteria for IIM.

Criteria Comments
1. Symmetrical weakness of limb girdle muscles

2. Elevated levels of muscle enzymes 3. Myopathy on EMG 4. Muscle biopsy evidence of inflammation 5. Skin rash in the case of DM

• Very simple

• Most widely known and used • Very sensitive • Least specific • Can only be used for DM and PM

Criteria PM
Myopathic DM
Amyopathic DM
Definite Probable Definite Probable Definite

Myopathic muscle weakness Yes Yes Yes Yes No
Electromyographic findings Myopathic Myopathic Myopathic Myopathic Myopathic or non-sepcific
Muscle enzymes High (up to 50 times normal) High (up to 50 times normal) High (up to 50 times normal) or normal High High (up to 10 times normal) or normal
Muscle biopsy findings Primary inflammation with the CD8/MHC-1 complex and no vacuoles Ubiquitous MHC-1 expression but no CD8 positive infiltrates or vacuoles Perifascicular, perimyseal or perivascular infiltrates; perifascicular atrophy Perifascicular, perimyseal or perivascular infiltrates; perifascicular atrophy Non-specific or diagnostic for DM (sub clinical myopathy)
Rash or calcinosis Absent Absent Present Not detected Present


These are the most commonly used medications used for myositis:

  • Corticosteroids - include mediations such as prednisone, methylprednisolone, prednisolone, and others. Acthar is a synthetic form of the hormone ACTH and is also used to treat myositis diseases.
  • Immunosuppressants. Immunosuppressants used in treating myositis include methotrexate, azathioprine, mycophenolate mofetil, cyclosporine, tacrolimus, cyclophosphamide, and hydroxychloroquine.
  • Immunoglobulin therapy - is a blood product derived from large pools of donated human plasma that contains the part of the blood that contains antibodies.[4]

Management / Interventions Physiotherapy

A key component for treatment is an early rehabilitation program with the inclusion of strength-building and aerobic exercises, in addition to a rigorous evaluation of these activities for remission of disease and the education of the patient and his/her caregivers[5].

Physical and occupational therapy are essential and along with orthotic devices if needed. These help patients improve mobility, retain motor function, prevent contractures that can arise and may help prevent steroids side effects like weight gain, osteoporosis, and type 2 fiber atrophy.

  • Strengthening programs twice weekly can be started as early as 2–3 weeks from the acute phase.
  • With severe cases, passive range of motion exercises can be done for 3 months, until strength improve; at which point strengthening exercises are initiated. There is growing evidence for safety and beneficial effects of physiotherapy and home exercise programs in myositis .

A recent study demonstrated the effect of a 12-week aerobic exercise program in 10 children IMM's. At the end of this longitudinal study, the subjects showed an improvement in muscle strength and function, aerobic conditioning, and a better quality of life[2].

There is a strong association between aerobic capacity and general health, both in healthy individuals and those with myositis. Regular physical activity and exercise can improve one’s quality of life and reduce the risk of serious chronic diseases, such as type II diabetes, osteoporosis, hypertension, and cardiovascular disease. These are all complications of myositis diseases or their treatment, so exercise is doubly important.[4]

The below video is a great first in the series of exercises for myositis from the myositis society. It links on to further exercises in course.


Education is also important for the client and caregivers/family. This can include education on the following aspects

  • Food pyramid usda.jpg
    Diet and nutrition
  • Sun protection
  • Mind and body practices
  • Self-care practices


  1. 1.0 1.1 Gazeley DJ, Cronin ME. Diagnosis and treatment of the idiopathic inflammatory myopathies. Therapeutic advances in musculoskeletal disease. 2011 Dec;3(6):315-24. Available from: (last accessed 9.12.2019)
  2. 2.0 2.1 2.2 2.3 Malik A, Hayat G, Kalia JS, Guzman MA. Idiopathic inflammatory myopathies: clinical approach and management. Frontiers in neurology. 2016 May 20;7:64. Available from: (last accessed 9.12.2019)
  3. Mayo clinic Living well with IM Available from: (last accessed 9.12.2019)
  4. 4.0 4.1 The myositis association Myositis Available from: (last accessed 9.12.2019)
  5. Souza FH, Araújo DB, Vilela VS, Bezerra MC, Simões RS, Bernardo WM, Miossi R, Cunha BM, Shinjo SK. Guidelines of the Brazilian Society of Rheumatology for the treatment of systemic autoimmune myopathies. Advances in Rheumatology. 2019;59. Available from: (last accessed 9.12,2019)
  6. Myositis association Myositis exercises Available from: (last accessed 9.12.2019)