Last Updated on August 2, 2019
Myositis can be caused by infection, injury, certain medicines, exercise, and chronic disease and is characterized by a chronic, progressive, inflammatory disease which most often is indicated by muscle weakness and other associated symptoms.
Muscle weakness, sometimes with muscle pain and general tiredness and fatigue are general features of the condition.
It can be chronic persistent or in an acute form.
Myositis and its subtypes are rare diseases. It can affect people of any age but are most common in children between 5 and 15 years of age and most adults are between 30 and 60 years of age.
Most of the these affect more women than men with the exception being inclusion body myositis, which affects more men than women.
There is currently no known cure for any form of myositis, however, with proper, expeditious treatment, some patients may experience partial or complete remission.
There are also refractory cases in which patients do not respond to the typical medications.
Types of Myositis
Idiopathic
In this group, the cause of the muscle inflammation is unknown. There are three major types
- Dermatomyositis
- Polymyositis
- Inclusion body myositis
Others are
- Juvenile Dermatomyositis and Juvenile Polymyositis
- Necrotizing Autoimmune Myopathy
- Orbital or Ocular
Polymyositis and dermatomyositis are most common in women, whereas inclusion body myositis affects men more often.
Polymyositis and dermatomyositis are autoimmune disorders.
In inclusion body myositis, the muscle contains tiny structures that resemble viral particles (called inclusion bodies), although no viral infection has been identified in association with this disease.
Conditions quite similar to polymyositis or dermatomyositis may accompany other autoimmune diseases.
Antisynthetase syndrome and mixed connective tissue disease are such disorders.
Muscle weakness can develop over a period of days, weeks, or months, is typically symmetrical, and affects proximal muscles, such as the quadriceps, hip flexors, neck, and deltoid muscles.
There is often difficulty in climbing stairs, rising from a chair or the floor, turning in bed, lifting, styling hair, or reaching over the head for something like an item on a shelf.
Dysphagia may occur in some people.
In addition to muscle weakness, dermatomyositis is characterized by a rash of the skin.
Inclusion body myositis causes slow, progressive, asymmetrical weakness and atrophy of the muscles of the wrists and fingers, muscles in the front of the thigh, and dorsiflexors of ankle and feet. Therefore the patients lose the ability to walk, suffer frequent falls and injuries, lose hand function, and have swallowing difficulties.
Juvenile dermatomyositis affects children in childhood or the teen years.
Orbital or Ocular myositis affects the extraocular muscles of the eye,
Necrotizing Autoimmune Myopathy has symptoms similar to polymyositis.
Mixed connective tissue disease is considered as an overlap of three diseases, systemic lupus erythematosus, scleroderma, and polymyositis.
Infectious
Some viral infections may cause myositis. Myositis also can be caused by parasites infection like trichinosis.
Pyomyositis is a bacterial infection that causes pus formation inside a muscle. It usually is caused by Staphylococcus bacteria.
It is seen in tropical climates and people who inject drugs.
Benign Acute Myositis
In benign acute myositis, a young child suddenly develops severe leg pain and cannot walk normally. These symptoms are dramatic and frightening, but they usually disappear within a few days. Benign acute myositis usually occurs in children who are recovering from the flu or some other respiratory infection caused by a virus.
Myositis ossificans
Myositis ossificans or heterotopic ossification is extra-skeletal ossification that occurs in muscles & other soft tissues. It is now denoted by better term heterotopic ossification. It affects the function of the normal soft tissues around bones and joints.
Drug-induced
In drug-induced myositis, muscle inflammation occurs as a side effect of a medication or a combination of medicines. This is rare.
Cholesterol-lowering drugs called statins, [atorvastatin, lovastatin, and simvastatin] and zidovudine used for HIV/AIDS are among others known to be associated with myositis.
Clinical Presentation
Symptoms of myositis can include muscle weakness, muscle pain, and muscle tenderness. Other symptoms vary, depending on the specific cause of myositis.
Idiopathic inflammatory myopathies typically cause painless, slowly progressive muscle weakness though 40% of people may have pain too.
In polymyositis and dermatomyositis affects proximal muscles including the muscles of the neck, shoulders, and hips. Some patients also have difficulty swallowing.
In dermatomyositis, skin symptoms like purple discoloration of the eyelids, a red rash on the face and neck, or scaly patches, usually on the knuckles may accompany.
In inclusion body myositis, weakness typically starts in the upper legs and later affects the upper arms and muscles farther away from the center of the body. Swallowing may be difficult.
Infectious myositis presents with muscle aches and flu-like symptoms when associated with viral flu.
When caused by trichinosis, symptoms in the early stages include diarrhea and vomiting. Later, as the parasites invade the muscles, symptoms can include fever, eye redness with swelling in the lids and muscle pain.
Patients with pyomyositis usually have a fever, and the muscle is painful, tender and slightly swollen. Skin over the muscle may be red and hot.
In benign acute myositis, there would be trouble walking and complains of calf muscles pain. There would be a history of recent fever, runny nose, sore throat, and other upper respiratory symptoms.
In the case of drug-induced myositis, the symptoms usually begin soon after a person starts taking a new drug or a combination of drugs. A detailed history of drug intake should be noted.
Lab Studies
General lab tests to know CBC, ESR, C reactive protein to look for infection
Enzyme Levels
Often, but not always, patients with myositis have elevated levels of enzymes found in the muscle which may indicate the presence of muscle damage. The enzymes are also found in the other tissues like liver and clinical context and correlation is very important.
- Aldolase
- Alanine aminotransferase or serum glutamate pyruvate transaminase [ALT or SGPT]
- Aspartate aminotransferase or serum glutamic-oxaloacetic transaminase [AST or SGOT]
- Creatine Phosphokinase
- Lactate dehydrogenase
Antibody Tests
ANA
Antinuclear antibody is found in autoimmune disorders that affect many tissues and organs throughout the body.
Myositis-Specific Antibodies
It is estimated that more than 50% of these patients have Myositis-specific antibodies.
Biopsy
A muscle biopsy is performed to assess the musculoskeletal system for abnormalities.
The muscles often selected for sampling are the biceps, deltoid or quadriceps.
The biopsy could be needle muscle biopsy or surgical muscle biopsy.
Skin Biopsy in case of dermatomyositis and rule out other disorders, such as Lupus. If the skin biopsy confirms the diagnosis, a muscle biopsy may be unnecessary.
EMG (Electromyography)
An electromyography is performed by inserting a thin needle electrode through the skin into muscles. Electrical activity is measured and recorded as muscles are tensed and relaxed. The needle is moved to different locations in the same muscle. One or more muscles may be tested.
MRI
It helps to identify the abnormal muscle tissue and can be used to locate the best site for a biopsy to establish the site for biopsy
Tests for Lung Diseases
Xray is the basic investigation to look for changes in the lung tissue. Pulmonary function tests would tell about the functional aspects of the lung. For those with lung involvement, this test may be performed at various intervals to determine improvement or disease progression.
Treatment of Myositis
For Idiopathic inflammatory myopathies following options are available
- Corticosteroids drug, such as prednisone
- Methotrexate
- Azathioprine
- Intravenous immunoglobulin
- Severe cases
- Muscle weakness causing life-threatening breathing or swallowing problems
- Other medications
- Cyclosporine
- Rituximab
- Mycophenolate mofetil
- Cyclophosphamide.
There is no reliably effective treatment for inclusion body myositis.
For the one associated with autoimmune disease, treatment of the underlying disease may be helpful
It is very important to maintain gentle muscle and joint movement, particularly in cases where myositis develops during childhood to prevent joint stiffness.
As the condition is brought under control, a gentle exercise programme can be started and gradually increased following the advice of a physiotherapist.
Infectious myositis of viral origin would be relieved when flu goes away.
Antiparasitic medication like albendazole will kill the trichinosis parasites.
For pyomyositis, drainage of the abscess by making an incision or by inserting a needle may be required in addition to antibiotics.
Benign acute myositis is self-limiting condition. Medication for pain may be required. The child gets better within a few days.
Myositis ossificans needs rest and anti-inflammatory medication. It may regress on its own or if it makes the joint stiff, surgical removal may be contemplated.
Drug-induced myositis will improve with stopping the causative drug.
Prognosis
The outlook varies, depending on the type.
With proper treatment, most people with polymyositis or dermatomyositis eventually regain at least some muscle strength. Often, muscle strength returns to normal. Typically, inclusion body myositis does not improve with treatment.
Progression of the illness may lead to complications like swallowing or breathing problems. Eventually, some patients need a support to walk or may need a wheelchair.
Medications taken to treat these muscle diseases may cause complications that affect prognosis.
Other types generally have a good prognosis.
