polymyositis

By Dr. M. Walravens, rheumatologist, O.L.Vrouw-Clinic Aalst

What is polymyositis (PM)?
What is dermatomyositis (DM)?
Most important symptoms
PM/DM in children
PM/DM in adults
PM/DM and cancer
PM/DM and viruses
Drug-induced PM/DM
PM/DM and other diseases
Localised PM
Diagnosis
Auto-antibodies
Treatment
Prognosis
Heredity

What is polymyositis (PM)?
Polymyositis is aa inflammation of the muscles due to a autoimmune reaction
What is dermatomyositis (DM)?
When polymyositis is accompanied by a skin inflammation, the term dermatomyositis is used (derma = skin).
Most important symptoms
The first symptom is mostly muscle weakness at the height of the pelvic muscles, which results in difficulties with climbing stairs, riding a bicycle, etc. At the same time or shortly afterwards, the same complaints occur in neck and shoulder girdle muscles. Strength loss in muscles may vary, ranging from mild to severe to paralysis. More or less significant muscle pain may be present. Skin manifestations are usually present in the early phase of the disease and they may even precede the muscle problems. In some cases the muscle problems are less important than the skin manifestations. Typical skin symptoms are erythema (redness) and swelling of the skin by oedema (accumulation of excessive amount of fluid in tissues). These symptoms occur on spots exposed to sunlight, but may also be limited to some skin rashes, e.g. on the face. At the height of the extensor side of the fingers and knuckles, a typical reddish to purplish swelling of the skin, sometimes scurfy, occurs in 1 patient out of 3. Another symptom is the red-purplish discoloration of the eyelids, as well as swelling and redness around the fingernail borders, which hurts when they tap a hard surface. Inflammations of the joints with swelling, but without damage to the cartilage or bone occur. Since the heart is also a muscle, it is often involved. In most cases this damage is limited and does not cause problems. Occasionally, it can lead to significant heart impairment. Shortness of breath may occur early, either due to lung involvement or due to involvement of the respiratory muscles. Swallowing difficulties occur sometimes. Kidney involvement is rare and certainly not typical.
PM/DM in children
This disorder is mostly more serious in children than in adults. The course of the disease is characterised by a less favourable outlook, a higher mortality rate, resistance to cortisone treatment, a generalised involvement not only of the muscles and skin, but also of other organs, and especially the gastrointestinal tract, the heart and lungs. Very typical are the intestinal perforations caused by vasculitis (inflammation of the blood vessels) in the intestinal wall. Very serious generalised types (type Banker and Victor) are different from the more chronical type (type Brunstig), which only causes muscle involvement. Both types often evolve into generalised muscle fibrosis (increased formation of connective tissue in the muscle) and muscle calcification, which lead to very significant limitation of motor functions and invalidity.
PM/DM in adults
There is a difference between the acute and chronical (or subacute) form. The acute form is more prevalent in young people and is characterised by a more generalised involvement of muscles, skin, the typical red-purplish discoloration of knuckles and eyelids, with possibly heart and lung damage, swallowing difficulties, vasculitis, fever, a general feeling of being ill and weight loss. This type is less frequent than the chronical (or subacute) type. An intensive and early treatment determines the outcome of the disease. If the disease is not treated, the mortality rate is 7 to 8 out of 10. An early and intensive treatment has reduced this rate to 2 out of 10. The chronical type occurs especially in women between 40 and 60
PM/DM and cancer
Sometimes people with dermatomyositis have tumours that are related to their dermatomyositis. That is why screening for such tumours has to be performed in the early phase of the disease. Men mostly develop a tumour e.g. in the lungs, stomach or prostate, while women are more likely to develop breast- or ovary cancer. Other types of tumours may also occur. In this group more men than women are affected, which indicates that this type is a separate entity. In general, these types of DM are very serious and often the patient dies of his DM and not of the cancer. In most cases, removing the tumour does not improve the DM.
PM/DM and viruses
Scientists have strong evidence that the Coxsackie B virus plays a role in the onset of PM/DM. This was demonstrated by tracing antibodies in the serum and by tracing the virus in the muscle tissue. Other viruses are also suspect.
Drug-induced PM/DM
This type is very rare. About twenty cases have been reported after they had taken D-Penicillamine. When the treatment with this drug is discontinued, the symptoms disappear. Other cases after administration of cimetidine, penicillin, procainamide, hydralazine and propylthiouracil have been reported. Syndromes similar to PM/DM were seen after patients had taken drugs to lower the cholesterol level.
PM/DM and other diseases
PM/DM can occur as a part of other connective tissue diseases. Also other autoimmune diseases like Hashimoto thyroiditis (autoimmune inflammation of the thyroid gland) and pemphigus (autoimmune skin disease) may occur together with PM/DM.
Localised PM
PM only rarely involves just one muscle or muscle group, but it is possible that e.g. only one limb is inflamed.
Diagnosis
There is no single diagnostic test for PM/DM. The diagnosis is made when there are sufficient symptoms of the disease present. These are: Typical symptoms at the level of the shoulders and/or pelvic muscles with distinctive skin manifestations Signs of inflammation and muscle necrosis on a muscle biopsy Increased amount of muscle enzymes in the serum Signs of muscle damage or damage to nerve ends on an electromyography If two of these criteria are satisfied, it is possible to make a diagnosis, but none of the criteria (not even the increase of muscle enzymes) are necessary to be able to make a diagnosis.
Autoantibodies
Antinuclear antibodies are present in 67 % of the patients. Detailed tests sometimes show antibodies against a specific nucleus or cytoplasmatic (cytoplasm = part of the cell outside the nucleus, but inside the cell wall) antigens, namely PM1 (30 to 50% in PM, 5 to 10% in DM), Mi2 (5 to 10% in DM), Jo1 (10 to 30% in PM, especially with lung damage). These antibodies are a diagnostic aid but it does not imply that if they are not present, the diagnosis of the disease cannot be made.
Treatment
In acute PM/DM with severe complaints, quick and intensive treatment is necessary with high to very high doses of corticosteroids. The stage and severity of the disease determines the duration and the dose of the medication. Sometimes immunosuppressives have to be added to the corticosteroid treatment. Mostly azathioprine (Imuran) is used in fairly high doses (up to 3mg/kg-body weight each day). This enables the steroid dose to be reduced more quickly. Other medications used are methotrexatum (Ledertrexate) or cyclophosphamide (Endoxan). Cyclosporine is reserved for those individuals who have the most severe flares of PM/DM and for those who don't respond or respond wrongly to other drugs. Kinesitherapy and physiotherapy are of uttermost importance to prevent permanent damage. Sufficient muscle training is also important, and the training program depends on the evolution of the disease.
Prognosis
PM/DM is a very serious disease and can occasionally be fatal (15 % approximately). Significant residual damage may be caused like muscle contractions and malformations. The prognosis has improved considerably the past few years. The most important reason for this is an early diagnosis and treatment. If the first flare is suppressed, a permanent remission is seen in 60% of the cases after 2 to 5 years. This means that PM/DM is characterised by only one major flare, but it is this flare that can be (life) threatening.
Heredity
PM/DM is not hereditary, although there is a genetic susceptibility. Like in other autoimmune diseases, there is a link with the presence of the HLA haplotype A1/B8/DR3 (HLA is the abbreviation of Human Leukocyte Antigen). The role it plays in the development of the autoimmune diseases is still unknown. Another factor, such as e.g. a virus, is believed to play a role together with the genetic susceptibility to the disease.

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