Polymyositis
Information on the causes, symptoms, diagnostic studies, and treatments of skeletal muscle inflammation.
Symptoms and Causes
Polymyositis is a chronic inflammation of the skeletal muscles, which are attached to the bones and are responsible for voluntary body movement. This condition causes severe muscle weakness and fatigue.
The prognosis of polymyositis is variable, as it depends on the stage of disease progression and the patient’s individual characteristics. In most cases, treatment helps restore muscle strength, allowing patients to resume their daily activities without affecting quality of life or life expectancy.
Symptoms
The most prominent symptoms of polymyositis are:
- Muscle weakness: occurs symmetrically on both sides of the body and progresses gradually. It is more common in the shoulders, hips, and thighs (proximal muscles).
- Morning muscle and/or joint stiffness (upon awakening or after periods of inactivity).
- Generalized fatigue.
- Shortness of breath.
- Dysphagia: difficulty swallowing when the muscles involved in deglutition are affected.
- Voice changes.
- General malaise.
- Muscle pain.
- Fever.
- Progressive weight loss.
Causes
The causes of polymyositis are not fully understood. It is classified among idiopathic inflammatory myopathies, as studies indicate that it is an autoimmune disease in which the immune system mistakenly attacks the body’s muscles.
This immune response may be associated with:
- Abnormal T-cell activity (a type of white blood cell) targeting unidentified muscle antigens, leading to inflammation.
- Viral infection.
- Connective tissue disorders.
- Certain types of cancer.
Risk factors
The risk of developing polymyositis increases in the following situations:
- Age: it usually occurs between 30 and 60 years of age, although it is more common after the age of 50.
- Sex: it is more frequent in women.
- Genetic predisposition.
- Autoimmune diseases: systemic lupus erythematosus, Sjögren’s syndrome, rheumatoid arthritis, scleroderma.
- Persistent infections.
- HIV.
Complications
Polymyositis may lead to the following complications:
- Malnutrition due to swallowing difficulties.
- Aspiration pneumonia (passage of food or saliva into the lungs).
- Cardiac involvement (myocarditis, arrhythmias).
- Respiratory failure.
- Muscle calcifications.
- Muscle atrophy.
Prevention
As an autoimmune condition, polymyositis cannot be prevented.
Which specialist treats polymyositis?
Polymyositis is a rheumatologic disease. Its management involves rheumatology, with the collaboration of physical therapists and, in some cases, speech-language therapy.
Diagnosis
The diagnosis of polymyositis requires a comprehensive approach combining different assessments. The most commonly used are:
- Physical examination: evaluation of symptoms, muscle strength, and joint function.
- Blood tests: elevated serum levels of creatine kinase (CK) and aldolase indicate muscle inflammation. In addition, antibodies associated with inflammatory myopathies and polymyositis may be detected.
- Electromyography (EMG): a fine needle electrode is inserted into the muscle to measure electrical activity during contraction and relaxation. Abnormal patterns suggest muscle disease.
- Magnetic resonance imaging (MRI): images obtained using radio waves and a magnetic field allow the detection of inflammatory processes.
- Muscle biopsy: a muscle tissue sample is obtained for laboratory analysis. Findings suggestive of polymyositis include:
- Tissue damage.
- Inflammatory cells (lymphocytes, macrophages).
- MHC-I expression in intact muscle fibers.
- Muscle atrophy.
- Necrosis: cell death.
Polymyositis can be classified into three different types according to the Bohan and Peter diagnostic certainty criteria:
- Definite polymyositis: the disease is confirmed based on the following findings (all four criteria are met):
- Clinical: muscle weakness and elevated muscle enzyme levels in the blood.
- EMG: electromyographic pattern consistent with muscle disease.
- Biopsy: evidence of muscle inflammation and damage.
- Probable polymyositis: a high likelihood of disease based on two possible profiles (three of the four criteria are met):
- Typical clinical presentation and compatible EMG findings, but minimal evidence of inflammation on biopsy.
- Atypical clinical presentation for polymyositis, compatible EMG findings, and evidence of inflammation and necrosis on biopsy.
- Possible polymyositis: the disease may be present because clinical findings and EMG are compatible, but the biopsy is normal (two of the four criteria are met).
Treatment
Polymyositis has no cure; therefore, treatment focuses on controlling and alleviating symptoms. The most effective strategies to improve patients’ quality of life include:
- Pharmacological treatment:
- Corticosteroids to reduce inflammation, with the possibility of gradual dose reduction if symptoms are controlled.
- Immunosuppressive agents to prevent the immune system from attacking muscle tissue, thereby minimizing muscle damage.
- Biologic agents: microorganisms are used to manage symptoms when conventional medications fail to achieve the desired results.
- Physical therapy: a combination of exercise and manual therapy to maintain muscle strength, flexibility, and range of motion. In the long term, it helps prevent muscle atrophy.
- Speech therapy: strategies are taught to compensate for muscle changes that interfere with swallowing and speech.
Polymyositis is a chronic disease and therefore requires lifelong treatment, along with regular medical follow-up to monitor disease progression and adjust therapy when necessary. During these periodic visits, particular attention is paid to the patient’s nutritional status, which may be compromised due to swallowing difficulties.
