Polymyositis and Dermatomyositis: Causes, Symptoms And Treatment

Polymyositis and dermatomyositis are immunogenic idiopathic myositis, i.e. autoimmune diseases in which the body's immunity is directed against its own cells. More specifically, the muscle fibres.

The two diseases are close, but there are some differences.

Polymyositis - PM, dermatomyositis - DM.

The basis of both forms is an inflammatory and degenerative process that affects the muscles. Dermatomyositis also involves damage to small blood vessels and skin damage with typical skin manifestations.

Muscle problems occur mostly subacutely over several weeks, or chronically, i.e. over a longer time period. The acute course of the disease is rare, but even more severe.

Rare autoimmune rheumatic diseases that affect approximately 7 in 1,000,000 people each year.

The disease affects both sexes, with a slightly higher incidence in women. It can occur at any age and in children.

Early diagnosis and timely treatment are important for all cases.

Want to know more about polymyositis and dermatomyositis?

Polymyositis

This autoimmune disease is characterized by an inflammatory process that is directed against muscle fibre cells - transverse striated muscle.

It is a type of myopathy.

Cellular immunity, CD8+ cytotoxic lymphocytes destroy muscle cells and cause them to die.

The disease occurs mostly in adults after the age of 18.
The period of peak occurrence os reported to be between 40 and 60 years of age.
Juvenile polymyziotis is rare.

Juvenile = young, not yet sexually mature. 
The term refers to diseases that developed in children before the age of 16.

PM is approximately 2.5 times more common in women.

It is characterized by muscle weakness, especially in the higher parts of the muscle groups. The course of the disease varies over a longer period of time.

Subacute = several weeks. 
Chronic = long-term, months, years. 
Acute - abrupt, but this form is very rare. 

Muscle pain may be present but is not necessary.
It is reported to occur in about a third of cases.

Along with polymyositis, in some cases they develop extramuscular problems  and damage to other systems. Fortunately, such cases represent a small percentage.

About 10% of polymyositis co-occurs with other autoimmune rheumatic connective tissue diseases, such as:

• systemic lupus erythematosus
• Sjögren syndrome
• reumatoid arthritis
• also
  • Crohn's disease
  • Bekhterev's disease
  • vasculitis
  • myasthenia gravis
  • primary biliary cirrhosis
  • Hashimoto's thyroiditis
  • psoriasis
  • and others

There is also a risk of co-occurrence with oncological diseases such as paraneoplastic polymyositis. Examples are malignant thymomas, bronchogenic carcinoma, pancreatic carcinoma, cancer of the stomach, bladder, colon and rectum or liver and others.

Dermatomyositis

It is also an autoimmune disease, however, it is not caused by cellular immunity, but humoral. The difference is also that the inflammatory process affects the smallest vessels of muscle fibres.

More precisely, the endothelium of endomysial capillaries, but also other small vessels.

Disruption of microcirculation, ie these small vessels, results in insufficient blood flow to the muscles. The risk of more severe vascular destruction is complete non-bleeding of muscle fibres - microinfarction and death, ie necrosis.

Dermatomyositis usually occurs in the adult population as an adult form. It is stated that the main peak is between 45 and 65 years of age.

It develops less often in childhood, then it is referred to as juvenile dermatomyositis (JDM), beginning in children aged between 5 and 15.

As with PM, it is usually manifested by muscle weakness. Muscle pain occurs mostly in children and in the acute form in adulthood.

The biggest difference compared to polymyositis is...

In addition to muscle problems, dermatomyositis also has skin symptoms. That is why "dermato" is in the name.

These skin changes have a typical manifestation of the disease - heliotrope rash and Gottron papules.

In the pediatric form of JDM, 50% is associated with calcinosis.

In addition, dermatomyositis is reported to develop pulmonary fibrosis in about 10% of cases. Also, necrotizing vasculitis of the gastrointestinal tract (digestive system) and the eyes as well as other extramuscular and extra-skin problems, such as heart disease.

DM + other autoimmune diseases, such as PM.

Please note that the disease can appear after 40 years of age, since there is an increased risk of oncological disease. This represents approximately 6-45% of cases of, for example, cancer of the lungs, colon, pancreas, ovarian cancer in women or prostate cancer in men.

Oncological diseases do not occur in people with juvenile dermatomyositis, i.e. in children.

Why do polymyositis and dermatomyositis occur? The cause of the disease is unknown.

As with other rheumatic diseases, genetic predisposition is reported to play a role. There might be a low familial factor. Direct inheritance is not present.

The influence of the external environment is on the genetic predisposition. In connection with it, it is claimed that the disease can arise as a result of infection (for example, a virus, bacteria), but also the action of toxins or medications.

The risk of triggering the disease is therefore:

• genetic predisposition and presence of HLA antigen
• infection by virus, bacteria, parasite
• exposure to toxins or certain drugs
• UVr radiation
• cancer in adults in PM in about 15% of cases and in DM in about 30% of cases

The diseases are not infectious, so they are not transmissible from person to person.

Polymyositis is based on the inflammatory process that cellular immunity produces. The autoimmune process, and thus the inflammatory reaction, directly damages the muscle fibres.

It's a little different with DM.

Dermatomyositis has a different mechanism of origin. Humoral immunity plays a major role here.

The inflammatory process affects the smallest muscle capillaries, but also other small blood vessels. The result is a microcirculation disorder that reduces blood flow to the muscle fibres.

A more serious condition is when the small blood vessels are damaged to such an extent that they are impassable. The muscle fibres are not supplied with blood, they develop ischemia and microinfarctions with the subsequent death of muscle fibres - necrosis.

Both conditions are characterized by typical problems.

The symptoms are mainly based on muscle damage. However, the forms have some differences.

Polymyositis presents with typical muscle manifestations.

Dermatomyositis also presents with skin problems.

The table shows the manifestations of both diseases

The diagnosis of both diseases is based on the medical history. The patient describes characteristic muscle weakness or other associated symptoms.

This is of course followed by muscle examinations, muscle tests and skin. Blood collection for laboratory tests, CK (serum creatine kinase), MB (myoglobin), MSA (myositis-specific-autoantibodies), and for example AST, ALT and others, including blood count, CRP.

Muscle tissue biopsy is important.

+ EMG (electromyography and muscle activity status) and MRI.

The diagnostic criteria developed by Bohan and Peter (1975) are used to diagnose DM. All 4 criteria are necessary, or 3 criteria + skin changes. If 2 criteria are confirmed, the diagnosis has a probabilistic value.

Diagnostic criteria for DM:

1. clinical criteria - muscle weakness, typical course with symptoms on the skin
2. increased serum creatokinase activity
3. EMG
4. muscle biopsy

Diagnostic criteria for PM:

1. clinical criteria - typical muscle weakness
2. increased creatine kinase activity
3. EMG
4. muscle biopsy

Confirmation of 4 critera = PM, in case of three, it is probable.

There are other classifications of these diseases.
For example, IBM - critera by Griggs et al. from 1995 
Dalakas and Hohlfeld in 2003 stated
that criteria B and P may also indicate other muscular dystrophies and myopathies.

Polymyositis usually develops after the age of 20. It has a gradual course that stretches over weeks to months. The first manifestations are fatigue and muscle weakness.

The course of the disease has a progressive character, whichmeans that the difficulties are gradually getting worse. Fever may be present in acute form. PM is less common in children.

Muscle weakness is present, a person is not able to raise his hands above the level of the shoulders and head over time, he does not hear. Walking uphill and stairs is also a problem, or the sufferer cannot stand up from a squat.

The patient needs support, is confined to a wheelchair, and every-day activities are severely limited. Although weakness in the lower limbs is not as common and intense as affecting the muscles of the upper half of the body.

Dermatomyositis is very similar, however, muscle problems are accompanied by skin damage. This has the typical symptoms when reddish to purple skin occurs over small joints or in the face, shoulders and upper back.

As far as duration is concerned, the course of the disease may be acute, but the disease usually develops over a longer period of time.

DM is characterized by the fact that it mostly affects children from 5 to 15 years of age or adults from 45 to 65 years. The pediatric form often presents with skin calcinosis when calcium is deposited in the skin and subcutaneous tissue, associated with its deformities.

Muscle pain is common in both forms, but it is not a condition.

Dermatomyositis is classified based on the course of the disease:

1. classic DM - classic muscle and skin symptoms are present
2. DM sine myositis 
   • hypomyopathic DM
     • without muscle weakness
     • presence of skin changes 6 months and longer
     • the presence of muscle damage and inflammation in laboratory tests
   • amyopathic DM
     • no muscle-related symptoms
     • skin changes for more than 6 months
     • without laboratory confirmation of muscle involvement
3. DM sine dermatitis - with minimal skin symptoms

After years of experienceing problems, the disease goes into remission and the symptoms withdraw. It is more common in children.

However, at any time there may be a relapse - a recurrence of problems.

What is the prognosis? It is more promising in children. But, of course, it depends on the overall course of the disease.

In children, the risk of death due to serious complications is low. Early detection and timely treatment are helpful circumstances.

In adults, especially the elderly, the risk of death is mainly due to severe muscle impairment, associated with aspiration pneumonia due to inhalation of food and gastric contents as a result of dysphagia. Intestinal vasculitis is another dangerous condition - inflammation of the vessels of the digestive tract in dermatomyositis.