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Inflammatory myopathies

Myopathy is a term used to describe muscle disease. The inflammatory myopathies are a group of diseases that involve chronic muscle inflammation, accompanied by muscle weakness. Another word for chronic inflammation of muscle tissue is myositis. The three main types of chronic, or persistent, inflammatory myopathy are polymyositis, dermatomyositis and inclusion body myositis.

Muscle inflammation may be caused by an allergic reaction, exposure to a toxic substance or medicine, another disease such as cancer or rheumatic conditions, or a virus or other infectious agent. The chronic inflammatory myopathies are idiopathic, meaning they have no known cause. They are thought to be autoimmune disorders, in which the body’s white blood cells, which normally fight disease, attack blood vessels, normal muscle fibers and connective tissue in organs, bones and joints.

These rare disorders affect both adults and children, although dermatomyositis is the most common chronic form in children. Polymyositis and dermatomyositis are more common in women than in men. A rare childhood onset form of polymyositis and dermatomyositis can occur in children between the ages of 2 and 15 years. Inclusion body myositis usually affects individuals over age 50.

Common Symptoms

  • Slow but progressive muscle weakness starting in the muscles closest to the trunk of the body, caused by inflammation damage to the muscle fibers
  • Fatigue after walking or standing
  • Tripping or falling
  • Difficulty swallowing or breathing
  • Slight muscle pain or muscles that are tender to touch


Polymyositis affects skeletal muscles – those involved with movement – on both sides of the body. Most cases occur in people between the ages of 31 and 60. In addition to symptoms listed above, progressive muscle weakness leads to difficulty swallowing, speaking, rising from a sitting position, climbing stairs, lifting objects or reaching overhead. People with polymyositis may also experience arthritis, shortness of breath and heart arrhythmias.

Dermatomyositis is characterized by a skin rash that precedes or accompanies progressive muscle weakness. The rash looks patchy, with purple or red discolorations, and characteristically develops on the eyelids and on muscles used to extend or straighten joints, including knuckles, elbows, knees and toes. Red rashes may also occur on the face, neck, shoulders, upper chest, back and other locations, and there may be swelling in the affected areas. Adults with dermatomyositis may experience weight loss or a low-grade fever, have inflamed lungs and be sensitive to light. Children and adults with dermatomyositis may develop calcium deposits, which appear as hard bumps under the skin or in the muscle (called calcinosis).

Inclusion body myositis (IBM) is characterized by progressive muscle weakness and wasting. The onset of muscle weakness is generally gradual, over months or years. Muscle weakness may affect only one side of the body. Falling and tripping are usually the first noticeable symptoms of IBM. For some individuals the disorder begins with weakness in the wrists and fingers that causes difficulty with pinching, buttoning and gripping objects. There may be weakness of the wrist and finger muscles and atrophy (thinning or loss of muscle bulk) of the forearm muscles and quadricep muscles in the legs.

Juvenile myositis has some similarities to adult dermatomyositis and polymyositis. It typically affects children ages 2 to 15 years, with symptoms that include proximal muscle weakness and inflammation, edema (an abnormal collection of fluids within body tissues that causes swelling), muscle pain, fatigue, skin rashes, abdominal pain, fever and shortening of the muscles or tendons around joints, which prevents free movement. Children with juvenile myositis may also have difficulty swallowing and breathing, and the heart may be affected.

Diagnosis

Diagnosis is based on the individual’s medical history, results of a physical exam and tests of muscle strength and blood samples that show elevated levels of various muscle enzymes and auto-antibodies. Diagnostic tools include:

  • Electromyography (EMG)
  • Ultrasound to check for muscle inflammation
  • MRI to evaluate muscle disease
  • Muscle biopsy for signs of inflammation, muscle fiber death or other changes
  • Skin biopsy for patients with dermatomyositis


Treatment

While chronic inflammatory myopathies can’t be cured in most adults, many of the symptoms can be treated. If left untreated, inflammatory myopathy can cause permanent disability. Options for treatment include:

  • Medication
  • Physical therapy
  • Exercise
  • Heat therapy
  • Orthotics and assistive devices
  • Rest


There is no standard course of treatment for IBM. The disease is generally unresponsive to corticosteroids and immunosuppressive drugs. Physical therapy may be helpful in maintaining mobility. Other therapy is symptomatic and supportive.

Source: National Institute of Neurological Disorders and Stroke


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National Institute of Neurological Disorders and Stroke

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