The myopathies are neuromuscular disorders in which the primary symptom is muscle weakness due to dysfunction of muscle fiber. Other symptoms of myopathy can include include muscle cramps, stiffness, and spasm. Myopathies can be inherited (such as the muscular dystrophies) or acquired (such as common muscle cramps). Myopathies are grouped as follows: congenital myopathies: characterized by developmental delays in motor skills; skeletal and facial abnormalities are occasionally evident at birth
muscular dystrophies: characterized by progressive weakness in voluntary muscles; sometimes evident at birth
mitochondrial myopathies: caused by genetic abnormalities in mitochondria, cellular structures that control energy; include Kearns-Sayre syndrome, MELAS and MERRF
glycogen storage diseases of muscle: caused by mutations in genes controlling enzymes that metabolize glycogen and glucose (blood sugar); include Pompe’s, Andersen’s and Cori’s diseases
myoglobinurias: caused by disorders in the metabolism of a fuel (myoglobin) necessary for muscle work; include McArdle, Tarui, and DiMauro diseases
dermatomyositis: an inflammatory myopathy of skin and muscle
myositis ossificans: characterized by bone growing in muscle tissue
familial periodic paralysis: characterized by episodes of weakness in the arms and legs
polymyositis, inclusion body myositis, and related myopathies: inflammatory myopathies of skeletal muscle
neuromyotonia: characterized by alternating episodes of twitching and stiffness; and
stiff-man syndrome: characterized by episodes of rigidity and reflex spasms
common muscle cramps and stiffness, and
tetany: characterized by prolonged spasms of the arms and legs
The inflammatory myopathies are a group of muscle diseases that involve inflammation of the muscles or associated tissues, such as the blood vessels that supply the muscles. A myopathy is a muscle disease, and inflammation is a response to cell damage. The inflammatory process leads to destruction of muscle tissue, and is accompanied by weakness and sometimes pain. Over time, there can be loss of muscle bulk (atrophy).
The four main types of chronic, or long-term, inflammatory myopathies are:
inclusion body myositis
necrotizing autoimmune myopathy
Myositis, or general muscle inflammation, may be caused by:
autoimmune disorders in which the immune system attacks muscle
an allergic reaction following exposure to a toxic substance or medicine. Among the drugs that have been suspected of contributing to myositis are carticaine (a local anesthetic), penicillamine (a drug used to lower copper levels in the body), interferon-alpha (mostly used to treat cancer and hepatitis), cimetidine (used to treat ulcers), carbimazole (to treat thyroid disease), phenytoin (used to treat seizures), and growth hormone. The vaccine for hepatitis B also has been implicated in some cases.
a virus or other infectious organism such as bacteria or fungi. People with the HIV virus, which causes AIDS, can develop a myositis, as can people with a virus called HTLV-1. Some myositis cases have followed infection with the Coxsackie B virus.
Although the cause of many inflammatory myopathies is unknown, the majority are considered to be autoimmune disorders, in which the body’s immune response system that normally defends against infection and disease attacks its own muscle fibers, blood vessels, connective tissue, organs, or joints.
Inflammatory myopathies aren’t genetic disorders, although there may be genetic factors that make it more or less likely that an inflammatory myopathy will develop.
Signs and Symptoms
General symptoms of chronic inflammatory myopathy include slow but progressive muscle weakness. Inflammation damages the muscle fibers, which causes weakness, and may affect the arteries and blood vessels that pass through muscle. Other symptoms include fatigue after walking or standing, frequent episodes of tripping or falling, and difficulty swallowing or breathing. Some individuals may have muscle pain or muscles that are tender to touch.
Polymyositis affects skeletal muscles (the type involved in body movement) on both sides of the body. It is rarely seen in persons younger than age 20. Generally, the onset occurs between age 30 and 60.Signs and symptoms of polymyositis vary considerably from person to person, which can make it difficult to diagnose. Untreated progressive muscle weakness may lead to difficulty swallowing, speaking, rising from a sitting position, climbing stairs, lifting objects, or reaching overhead. Some people with polymyositis may also develop arthritis, shortness of breath, heart arrhythmias (irregular heartbeats), or congestive heart failure (when the heart is no longer able to pump out enough oxygen-rich blood).
Dermatomyositis is characterized by a skin rash that precedes or accompanies progressive muscle weakness. The rash appears 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. There may be swelling in the affected areas. The rash sometimes occurs without obvious muscle involvement and often becomes more evident with sun exposure.Adults with dermatomyositis may experience weight loss or a low-grade fever, have inflamed lungs, and be sensitive to light. Adult dermatomyositis, unlike polymyositis, may accompany tumors of the breast, lung, female genitalia, or bowel. Children and adults with dermatomyositis may develop calcium deposits, which appear as hard bumps under the skin or in the muscle (called calcinosis). Calcinosis most often occurs one to three years after disease onset but may occur many years later. These deposits are seen more often in childhood dermatomyositis than in dermatomyositis that begins in adulthood.In some cases of polymyositis and dermatomyositis, distal muscles, which are the muscles away from the center of the body, such as those in the forearms and around the ankles and wrists), may be affected as the disease progresses. Polymyositis and dermatomyositis may be associated with collagen-vascular or autoimmune diseases such as lupus. Polymyositis may also be associated with infectious disorders such as HIV, which causes AIDS.
Inclusion body myositis (IBM) is the most common form of inflammatory myopathy in people age 50 years and older and is characterized by slow, progressive muscle weakness and wasting over the course of months or years. IBM affects both proximal and distal muscles, typically in the thighs and forearms, and is often occurs on both sides of the body, although muscle weakness may affect only one side of the body. It also includes features of muscle degeneration with multi-protein aggregates (clumps) in the muscle that can contain toxins seen in Alzheimer’s disease and other neurodegenerative diseases.
Falling and tripping are usually the first noticeable symptoms. The disorder often begins with weakness in the wrists and fingers that causes difficulty with pinching, buttoning, and gripping objects. People may experience weakness in their wrist and finger muscles and atrophy (thinning or loss of muscle bulk) in their forearm muscles and quadriceps muscles in the thighs. Difficulty swallowing occurs in approximately half of IBM cases due to involvement of the throat muscles.
Symptoms of the disease usually begin after the age of 50, although the disease can occur earlier. Unlike polymyositis and dermatomyositis, IBM occurs more frequently in men than in women.
Necrotizing autoimmune myopathy (NAM) is a rare and relatively newly recognized subgroup of inflammatory myopathies. NAM can occur at any age but usually affects adults. Its symptoms are similar to polymyositis and dermatomyositis, with weakness in both the upper and lower body, difficulty rising from low chairs, climbing stairs, or lifting objects. However, the onset of these symptoms can be more severe and sudden, reaching their peak over a period of days or weeks. Other symptoms include fatigue, weight loss, and muscle pain.NAM occurs alone or after viral infections, in association with cancer, in people with connective-tissue disorders such as scleroderma, or, rarely, in people taking cholesterol lowering medications (statins). Muscle weakness and pain may continue to worsen even after individuals stop taking the drugs.
Childhood inflammatory myopathies have some similarities to adult dermatomyositis and polymyositis. They typically affect children ages 2 to 15 years. Symptoms 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 contractures. Contractures result from shortening of muscles or tendons around joints, are caused by inflammation in the muscle tendons, and prevent the joints from moving freely.Children with inflammatory myopathies may have difficulty swallowing and breathing. The heart may also be affected. Between 20 to 40 percent of children with juvenile dermatomyositis develop calcinosis, which can cause significant muscle weakness and pain, joint contracture, skin ulcers, and decreased muscle bulk.
Diagnosis is based on medical history, results of a physical examination that includes tests of muscle strength, and blood samples that show elevated levels of various muscle enzymes and autoantibodies. Diagnostic tools include:
electromyography to record the electrical activity generated by muscles during contraction and at rest
magnetic resonance imaging to reveal abnormal muscle anatomy.
A biopsy sample of muscle tissue should be examined for signs of chronic inflammation, muscle fiber death, vascular deformities, or other changes specific to the diagnosis of a particular type of inflammatory myopathy. A skin biopsy can show changes in the skin associated with dermatomyositis.
Chronic inflammatory myopathies cannot be cured in most adults but many of the symptoms can be treated. Options include:
orthotics and assistive devices
Dermatomyositis, polymyositis, and necrotizing autoimmune myopathy are first treated with high doses of corticosteroid drugs, such as prednisone. This is most often given as an oral medication but can be delivered intravenously.
Immunosuppressant drugs, such as azathioprine and methotrexate, may reduce inflammation in individuals who do not respond well to prednisone. Periodic treatment using intravenous immunoglobulin can increase the chance for recovery in individuals with dermatomyositis, polymyositis, or NAM. Other immunosuppressive agents that may treat the inflammation associated with dermatomyositis and polymyositis include cyclosporine A, cyclophosphamide, mycophenolate mofetil, and tacrolimus.
Injections of adrenocorticotropic hormone gel may be another option for people who do not respond to or cannot tolerate other drug treatment options. Biologic therapies such as rituximab or tumor necrosis factor (TNF) inhibitors such as infliximab or etanercept may be used in severe cases where other treatment options have failed. However, there are very few studies that have shown how well these agents treat polymyositis and dermatomyositis.
Physical therapy is usually recommended to prevent muscle atrophy as well as to maintain muscle strength and range of motion. Bed rest for an extended period of time should be avoided, as people may develop muscle atrophy, decreased muscle function, and joint contractures. A low-sodium diet may help to reduce edema (swelling) and cardiovascular (heart and blood vessel) complications. Occupational therapy can include an assessment of daily activities to address tasks such as feeding, bathing, and dressing.
Many individuals with dermatomyositis may need a topical ointment such as corticosteroids,tacrolimus, or pimecrolimus for their skin disorder. They should wear a high-protection sunscreen and protective clothing, particularly those who are light-sensitive. In rare instances, surgery may be required to remove calcium deposits that cause nerve pain and recurrent infections.
There is no standard, evidence-based course of treatment for inclusion body myositis. The disease is generally unresponsive to corticosteroids and immunosuppressive drugs. Some evidence suggests that immunosuppressive medications or intravenous immunoglobulin may have a slight, but short-lasting, beneficial effect in a small number of cases. Physical therapy may be helpful in maintaining mobility. Other therapy is symptomatic and supportive.
List of Medicines for PM & DM
corticosteroids prednisone tablets (Deltasone); intravenous methylprednisolone sodium succinate (Solu-Medrol): Dampens inflammation and immune response by interfering with processing of antigens and with early triggering of T-cell and B-cell production and later proliferation of B-cells and T-cells. These cells are produced by the immune system in autoimmune diseases such as PM and DM.
azathioprine (Imuran): Interferes with proliferation of B-cells and T-cells.
methotrexate (Rheumatrex, Folex, Mexate): Interferes with proliferation of B-cells and T-cells.
cyclosporine (Neoral, Sandimmune): Keeps T-cells from stimulating production of more T-cells and B-cells (“upstream” of azathioprine and methotrexate action).
cyclophosphamide (Cytoxan): Interferes with proliferation of B-cells and T-cells.
mycophenolate mofetil (CellCept): Interferes with proliferation of B-cells and T-cells.
tacrolimus (Prograf, old name FK506): Keeps T-cells from stimulating production of more T-cells and B-cells (“upstream” of azathioprine and methotrexate action).
hydroxychloroquine sulfate (Plaquenil):Mechanism not understood; used in arthritis, lupus, malaria; can be used to reduce steroid dosage in myositis, particularly in children.
infusion of mixed immunoglobulins; IVIg (Gammar, Gammagard, Sandoglobulin, others): Has complex actions on immune system, such as providing antibodies against patient’s own antibodies; interfering with immune-system reaction to antibody-marked cells; interfering with blood transported chemicals released by immune system; interfering with activation and maturation of T-cells and B-cells.
plasmapheresis: Removes antibodies and proteins made by the immune system from the blood and returns “cleansed” blood to patient.
In most cases, the symptoms of dermatomyositis resolve with therapy. The disease is usually more severe and resistant to therapy in individuals with heart problems. Approximately one-third of individuals with juvenile-onset dermatomyositis recover from their illness, one-third have a relapsing-remitting course of disease, and the other third have a more chronic course of illness.
The prognosis for polymyositis varies. Most individuals respond fairly well to therapy, but some people have a more severe disease that does not. These individuals may have significant disability. Since polymyositis can cause difficulty swallowing, people can become malnourished. They are also at increased risk for falling, which can lead to hip and other bone fractures, disability, or death. In rare cases people with severe and progressive muscle weakness can develop respiratory failure or pneumonia.
Although necrotizing autoimmune myopathy is more difficult to treat than polymyositis and dermatomyositis, it generally responds well to long-term combination immunosuppressive therapies.
IBM is generally resistant to all therapies and currently available treatments do little to slow its progression.
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