Myositis

Myositis refers to a group of chronic inflammatory muscle diseases characterized by muscle inflammation and progressive muscle weakness. The condition can affect various muscles, including those close to the trunk of the body (proximal muscles), such as the shoulders, upper arms, hips, and thighs.

Types of Myositis

• Polymyositis (PM): Affects the skeletal muscles, which are responsible for movement. It is more common in adults and can occur at any age.
• Dermatomyositis (DM): Characterized by skin rash and muscle weakness. The skin rash typically appears before or at the same time as the muscle weakness.
• Inclusion Body Myositis (IBM): The most common acquired myopathy in adults older than 50 years, characterized by progressive muscle weakness and wasting, especially in the fingers and quadriceps.
• Juvenile Dermatomyositis (JDM) and Juvenile Polymyositis (JPM): Variants of myositis that occur in children under the age of 18.

Causes and Risk Factors

The exact cause of myositis is unknown, but it is believed to be an autoimmune disease, where the body's immune system mistakenly attacks its own muscle tissues. Certain genetic and environmental factors may trigger the onset of the disease in susceptible individuals.

Symptoms

• Muscle weakness, particularly in the proximal muscles (shoulders, upper arms, hips, and thighs)
• Difficulty swallowing (dysphagia) or breathing due to muscle weakness
• Joint pain and stiffness
• Fatigue
• Skin rash (in dermatomyositis)
• Muscle wasting, especially in inclusion body myositis

Diagnosis

Diagnosing myositis involves a combination of the following:

• Medical history and physical examination
• Blood tests to detect elevated levels of muscle enzymes (such as creatine kinase) and autoantibodies
• Muscle biopsy to examine muscle tissue for signs of inflammation and damage
• Electromyography (EMG) to assess the electrical activity of muscles
• Imaging tests, such as MRI or CT scans, to evaluate muscle damage and rule out other conditions

Treatment

Treatment for myositis typically involves a combination of medications and therapies aimed at reducing inflammation, relieving symptoms, and improving muscle strength.

• Corticosteroids (such as prednisone) to reduce inflammation and suppress the immune system
• Immunosuppressive medications (such as methotrexate or azathioprine) to modify the disease course
• Physical therapy to maintain muscle strength and mobility
• Occupational therapy to adapt to any physical limitations
• Speech therapy, if swallowing difficulties are present

Prognosis and Complications

The prognosis for myositis varies depending on the type of disease, severity of symptoms, and response to treatment. Potential complications include:

• Muscle atrophy (wasting) and weakness
• Respiratory failure due to diaphragmatic weakness
• Swallowing difficulties (dysphagia)
• Osteoporosis, particularly with long-term corticosteroid use
• Increased risk of infections and malignancies