Inclusion Body Myositis (IBM Inclusion Body Myositis) 4.3/5 (23)

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Inclusion Body-myositis

Inclusion body myositis. Muscle atrophy (thin muscles) in forearms and thighs. Tissue sample with «rimmed vacuole» Illustration: Turner MR, Talbot K - Pract Neurol (2013). . CC BY NC 3.0


The disease is rare, has an unknown cause and develops gradually over months and years in people over the age of 50 (rarely before). Tissue sample from muscle is crucial for the diagnosis.


In Norway, it has been found that 33 / 100.000 has inclusion body myositis (prevalence) (reference: Dobloug C 2015). The disease is thus defined as one rare disease.

  • Men are attacked somewhat more often than women. 
  • The average age at diagnosis is 67 years (ref. Dobloug C, 2015).

Disease history

It often takes 6-8 years from symptom onset to final diagnosis.

  • The muscle strength of the thighs decreases
    • Many people are having trouble getting riding from squatting
    • Difficult to walk up stairs
    • Heavy to get up from a chair
  • Muscles in the forearms and legs often become thinner and weaker eventually
    • Not as weak in both body halves (asymmetric affection)
  • Some people get reduced swallow muscle function and swallowing problems
  • The fingers can get curved

Medical investigations

The physician assesses the muscle strength and muscle size of the legs and arms.

  • Walking on heels and toes can be difficult
  • Problematic to rise from squatting or from the chair without support
  • Thin arms and legs (distal muscle atrophy) (illustration above) and weakness: Finger flexors, grip function (usually non-dominant hand). Weaknesses, myalgia
  • The fingers may be bent (flexion position)
  • Dysphagia (swallowing problem) (30-60%)

No Antibodies in blood samples are available for routine testing (as of 2020). In a study, anti-cytosolic 5′-nucleotidase 1A (cN1A) showed 50% sensitivity (ability to detect IBM) (Felice KJ, 2018).

EMG / neurography can show myopathy changes

MRI of the thigh muscles

  • Changes that are quite characteristic (Reference: Tasca G, 2015)
    • Obvious loss of muscle (atrophy) and fat infiltration
    • Typical localization on the stretch side of the thigh muscles, especially the quadriceps muscles near the knee (distal to the thigh). Often a gradient with increasing changes closest to the knee
    • The sartorius muscles are also often attacked
    • The Recutus femoris muscle is not attacked in everyone
    • Muscles behind the thigh (flexor muscles) attack more variably and can be normal

In blood tests, creatine kinase (CK) is slightly elevated (often around 300)

  • Rarely CK more than 5 x upper reference level

X-ray of esophagus shows reduced swallowing function in approx. 60%

Muscle biopsy is essential for the diagnosis

Tissue sample

Biopsy / Histology: both degenerative and inflammatory features: endomyseal invasion of CD8 + lymphocyte, cytoplasmic and intranuclear inclusions. Amyloid in muscle fibers (crystal-violet staining) ("Alzheimer's in the muscles"). Light microscopy: Vacuoles (see illustration above), intra-nuclear and intra-cytoplasmic inclusions. Electron microscopy: Microtubular filaments in the inclusions. These are colored with Congo red, thioflavin and crystal violet (indicating amyloidosis)

Classification criteria


  • Unfortunately, drugs have little or no effect and side effects can outweigh the benefits, but response to treatment is different from person to person. Occasionally, a treatment attempt is made over 6 months.
  • Mapping of the disease and treatment goals must be outlined in advance. After impact assessment, it is considered whether further medical treatment is appropriate. Uncertain effect of corticosteroids (0-40%), even if CK values ​​improve
  • If treatment attempts with immunosuppressive drugs are done, the dosage is individual. One regime used is:
    • Prednisone 0,5-1mg / kg / day the first week, then reduction so that the dose is 10mg / d after a few weeks. This dose is maintained for up to 6 months 
    • Combined with Methotrexate 7,5mg - 25mg /week over 3 - 6 months or Imurel 1,5 - 2,5 mg / day
    • If not effect on muscle strength and progression after 6 months, one should consider discontinuing treatment.
    • There is no safe effect of Sendoxan, Leukeran, azathioprine (Imurel), Ciclosporin A) or methotrexate in most.
    • Octagam (immunoglobulin) can be attempted by severe affection of esophagus and swallowing difficulties (reference: Cherin, P, Pelletier, S, Neurology 2002)
  • Customized physical exercise and exercises (physiotherapist)
  • Aids for the best possible physical function (occupational therapist)
  • Prevention of fall (occupational therapist)
  • Proper diet and weight

Medical prognosis

The disease is not fatal, but after 5 years from the diagnosis many have to use crutches to go. After 10 years, the function is often further exacerbated (reference: Sedkul & Dalakas, Semin Neurol 1993)


Lundberg IE, 2017: EULAR Classification of myositis 

Norwegian Rheumatological Association



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