Myositis, muscle inflammation 4.78/5 (18)

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Myositis is muscle inflammation

Myositis can cause muscle weakness in the thighs and other muscle areas



Myocyte diseases are found in several types, all of which are characterized by rheumatic inflammation of the muscles

They are divided into several subgroups:

  • Dermato-myositis (ICD10 M33.1). The skin is also attacked (eczema), please see separate page here
    • Tissue test (biopsy) shows peri-fascicular rheumatic (autoimmune") inflammation or atrophy of muscle cells
  • Polymyocyte (ICD10 M33.2). Only muscle inflammation
    • Tissue test shows rheumatic inflammation mostly inside the muscle cells: Endo-myseal inflammation (accumulation of CD8 + T lymphocytes where some are observed inside non-dying cells). No vasculopathy or immune complex deposition

The fact that the tissue samples are different confirms that these conditions are also different diseases in the first place, but they are similar. Both conditions are characterized by chronic inflammation of the muscles and the treatment is quite similar.

In addition, there are special forms of myocyte. These include:

    • Some types of myositis do not fit into these sections and are termed "non-specific myositis" (reference: Basharat P, 2015).
    • Most often, the enzyme is CK (creatinekinase) and or Troponin T (cTnT) increased in blood sample
  • Viral myocyte (Virus myocyte) is most commonly seen in children and is rare (reference: Cardin P, 2015). Triggers can be Influenza A and B, H1N1 virus, Coxsackie virus, Epstein-Barr virus, Herpes simplex virus, Parainfluenza, Adeno virus, Echo virus, Cytomegaly virus (CMV), Meslinger virus, Varicella -Zoster, Human immunodeficiency virus (HIV), Dengue fever.
    • Debut 1-14 days after virus infection
    • Strong muscle aches
    • Often few muscle groups are attacked
    • CK can be very high (rhabdomyolysis)
    • Muscle biopsy often nonspecific
    • Effect of anti-viral treatment

Myositis must be distinguished from non-inflammatory disease, so-called "myopathies" which are often hereditary conditions (Muscular Dystrophy) without particular rheumatic inflammation. Neither must myositis be confused with Polymyalgia rheumatica or Non-inflammatory muscle pain syndromes and is also separated from "Rhabdomyolysis"Which is an acute muscle disease for another reason (see differential diagnoses).

Myosite Vastus_lateralis

"Vastus lateralis" is often attacked by myositis. by Original uploader was Chrizz at sv.wikipedia. CC BY SA 3.0

Disease Causes

The cause of myocyte is unknown in most cases (Idiopathic). In some cases, however, a cause is likely to be:

  • Some drugs and drugs
  • Dermatomyositis in adults is associated with the underlying cancer in some cases
  • When the disease is first started, we know that the body's own immune system accidentally attacks the muscles (polymyositis), possibly also the skin (dermatomyositis) of a autoimmune inflammation (Inflammation). Also internal organs, especially lungs (Antisynthetase syndrome, MDA5 syndrome) and the heart can be damaged. In severe muscular inflammation, the kidneys may fail
  • The treatment is to suppress the overactive immune system with immunosuppressive drugs


Myositis diseases are rare with 6-10 cases per 100.000 population (prevalence) (reference: Dobloug C, 2015). Myocyte is thus defined as one rare disease. The number of new people receiving the disease per year is estimated at 0,5-8 per million, which corresponds to approx. 25 new cases in Norway annually (incidence).

  • Women are attacked twice as frequently as men.
  • Most people get sick at the age of 50, but also children (most often Juvenile dermatomyositis) and older people can be attacked


Myositis symptoms develop gradually over weeks and months. Less than half experience pain in the muscles.


  • Gradually weakened muscle strength
    • Thigh muscles: Difficult to get up from squatting or sitting
    • Upper arms: heavy lifting arms over head
    • Neck: Head feels heavy to hold
  • Muscle pain may also have other causes, please read more here (in Danish).


The skin

The skin is attacked by Dermatomyositis, juvenile dermatomyositis (child) og MDA5 syndrome.

Swallowing problem

Reduced muscular function in the esophagus can cause a slight swallowing error or feel that larger pieces of food slip down poorly.

  • Some develop pneumonia or other damage to the lungs because food, drink and, in part, stomach acid get into the lungs. The esophagus is routinely examined with x-ray and / or gastroscopy.


Illustration: V sign is redness on neck and chest wood Dermatomyositis. Openi. Affiliation: Department of General Surgery, Changi General Hospital, Singapore. CC BY 4.0


Muscle strength

  • Reduced muscle strength not caused by pain
  • The thigh muscles (Quadriceps) are often slimmer in both legs

Blood tests

EMG (electromyography))

MRI (magnetic resonance imaging) of the thigh muscles

CT (computer tomography) of lungs

X-ray examination of esophagus (dynamic with contrast agent being swallowed)

Tissue sample (Biopsy) from the currently inflamed muscle should confirm the diagnosis

  • At myositis, tissue tests (muscle biopsy) show typical inflammatory changes (usually vastus lateralis on the thighs, see the illustration above)
  • Before the biopsy is often MRI scan done to locate the best place for biopsy
  • Dermato-myositis:  Tissue test (biopsy) shows peri-fascicular rheumatic (autoimmune") inflammation or atrophy of muscle cells
  • Polymyocyte: Tissue test shows rheumatic inflammation mostly inside the muscle cells: Endo-myseal inflammation (accumulation of CD8 + T lymphocytes where some are observed inside non-dying cells). No vasculopathy or immune complex deposition
  • More about changes in biopsy here (in Danish) (Neuropathology-web)

Criteria for diagnosis

Incorrect diagnosis (similar conditions, differential diagnoses)


Myocyte onset during pregnancy carries the risk of fetal damage. Some women with myositis have SSA antibody (as by Seagrass syndrome / pregnancy) which can cause heart problems (heart block) in the fetus. Low rashes in SSA are most commonly associated with myositis and carry lower risk than high rashes. In a quiet stage of illness my pregnancy has a good prognosis. Nevertheless, pregnancy in myocytes is generally perceived as "risk pregnancy". One should be followed up by the maternity ward and rheumatologist. Prior to a pregnancy, it is important that any drug use is reviewed by a specialist.

Myositis and diet

Not everyone has problems suggesting a changed diet, and a special myocyte diet does not exist.

  • If Esophagus (esophagus) Having reduced muscle function, swallowing can be a problem. Some also swallow "wrong" and get food or drink in the "larynx", that is trachea down to the lungs. Chew your food well and long. Drink for meals. Hard foods can be soaked in sauce or milk.
  • If you use cortisone medicines like Prednisolon, there is a risk Osteoporosis .
    • One should prevent with calcium and vitamin D supplements, such as Calcigran Forte chewable tablets.
    • Unhealthy lifestyle factors such as smoking and high alcohol consumption aggravate the risk of osteoporosis and fractures
  • Being overweight may be due to high Prednisolone doses, but great body weight is unhealthy for muscles, joints and overall physical function. Diet should have low calorie intake (fruits, vegetables, salads, chicken) combined with personalized physical activity.

Some people use antidepressants with Methotrexate or Salazopyrin (sulfasalazine) which counteract normally folic aciduptake from the intestine. Supplements with Folic Acid tablets are therefore recommended. Vegetables and fruits contain natural folic acid.

Combination of several immunosuppressive drugs (eg Prednisolone, Methotrexate, MabThera / Rixathon, Remicade / Remsima / Inflectra) increases the risk of infection.

  • Avoid foods that may contain bacteria. This can be raw meat, raw fish (sushi), raw eggs, non-pasteurized cheese, milk or unwashed vegetables.

Generally about diet in rheumatic diseases here (in Danish)


Before starting treatment, it is important that one is aware of the disease and the treatment objective and the side effects that may occur. Treatment goal is to stop the disease completely, ie obtain remission. Unfortunately, there is no treatment that heals the disease.


Lundberg IE, 2017: EULAR Classification of myositis 

Rheumatological Association / Legeforeningen 2020


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