Polymyositis is a chronic inflammatory disease of the skeletal muscle. It is a predominant form of muscular dystrophy, noticed among elderly people. It is categorized as one of the three important forms of myopathies that exist. The response to this condition varies from person to person depending on the strength and dexterity of the muscle tissue. Polymyositis is generally not localized and hence many muscle groups are affected by it.
The most common muscle groups affected by this disease are the muscles associated with the neck (sternocleido mastoid), shoulders (scapular region), trapezoid region, hands and legs mainly hams and quadriceps during walking and running. The symptoms of polymyositis are usually self-limiting. However in case of adverse muscular inflammation, medical attention is required in order to prevent progressive damage of the muscle tissue.
Clinical manifestations of Polymyositis
Polymyositis has many causes - some of the common causes include infections (bacterial or viral), and inherited forms. Viral myagias are one of the forms, which can affect the muscle tissues in an intense manner if ignored. The appropriate intervention for viral Myalgia causing Polymyositis is to identify the exact cause in ruling out other infective forms such as bacterial infection through laboratory diagnosis.
Viral particles can induce the onset of fever causing muscular weakness and fatigue. Sometimes, polymyositis can affect children under these scenarios. Other generalized clinical manifestations of the disease include low-grade fever, weakness, irritability, tenderness, decreased appetite and shortness of breath. Some forms of polymyositis have long-term effects and hence such patients are advised to incorporate immunosuppressive agents. This is recommended when Polymyositis takes the autoimmune disease form.
Diagnosis of Polymyositis
Polymyositis is predominantly diagnosed by the determination of biochemical values such as creatine kinase in the blood. Creatine kinase is produced in case of muscle cell damage, the estimation of which determines the extent of muscle damage caused. Electromyograph (EMG) is also recommended to understand the neuromuscular physiology and the disorders associated with them such as myogenic condition. This is identified by the neuromuscular electrical conduction studies.
In some cases, biopsy is recommended to understand the pathophysiology of the disease through histological anomalies. The specimen is usually taken from the quadriceps or shoulders (deltoid). The pathological identification includes the presence of infiltrated muscle cells and focal regions of muscular degeneration in the muscle fibers.
Treatment of Polymyositis
Polymyositis is predominantly treated by the administration of corticosteroids in order to reduce the inflammation. These drugs can be either given by oral route or through IV administration. Other forms of treatment include immunosuppressant administration in case of autoimmune form of the disease. Azathioprine and methotexrate are generally given as immune suppressants. Appropriate intervention through corticosteroids or immune suppressants can facilitate the motor recovery in neuromuscular conduction.
CK blood test
A Creatinine Kinase test is a blood test that measures the levels of Creatinine phosphokinase (CPK). It is an enzyme found predominantly in the heart tissue, brain and skeletal muscle. The CK blood test is commonly used to diagnose the existence of heart muscle damage. The CK blood test result shows an increase above normal in a person's blood test about six hours after the start of a heart attack.
It reaches its peak in about 18 hours and returns to normal in 24 to 36 hours. When the total CPK level is substantially elevated, then it is indicative of injury or stress to heart, brain or skeletal areas. The small amount of CPK that is normally in the blood comes from the muscles. The CPK blood test also helps in cost-effective management of people with suspected coronary atherosclerosis. It also evaluates the extent of muscle damage caused by drugs, trauma or immobility.
Abnormal CK-MB (one of three CK isoenzymes) or troponin levels are associated with Myocyte Necrosis and the diagnosis of Myocardial infarction. The Cardiac Markers of Cardiac Myocyte Necrosis (damage to the Cardiac muscle cells), myoglobin, CK, CK-MB and troponin I and T are primarily used to identify acute Myocardial Infarction.
It is used in early detection of dermatomyositis and polymyositis. It is also used to distinguish malignant hyperthermia from a post operative infection. It helps to discover carriers of muscular dystrophy.
The normal range for Creatinine Kinase (CK or CPK) blood test:
Male: 38 - 174 units/L
Female: 96 - 140 units/L
Increased levels of CK also can be found in viral myositis and hypothyroidism. Higher than normal CPK levels is indicative of the following conditions:
Serum CKMB levels are tested to check for myocardial injury. It is another important cardiac marker. The primary source of CKMB is myocardium although it is also found in skeletal muscle. Typically CKMB tests have now been replaced by Troponin test. But in cases of abnormal Troponin assay results or suspected re-infarction in the hospital, the CKMB serum test is still used.
High levels of CK MB are noticed in cases of polymyositis and rhabdomyolysis. Patients suffering pulmonary embolism, hypothyroidism, and muscular dystrophy or carbon monoxide poisoning can also show higher levels of serum CKMB. The reference range is about 56.2 pg/mL.
ANA blood test
Antinuclear antibodies (ANA) refer to the unusual antibodies that are detectable in the blood. ANA are gamma-globulins type of antibodies that are found in patients with certain autoimmune diseases. ANA are directed against certain components found in the nucleus of a cell in the body. These antibodies have the capacity of binding certain structures within the nucleus of the cells. The ANA test was first designed by Dr.George Friou in 1957. The laboratory blood test exposes the antibodies in the serum of the blood to cells. It is then determined whether or not antibodies are present that react to various parts of the nucleus of cells. Hence the term 'anti-nuclear' antibody is used.
Fluorescence techniques are adopted to detect the ANA antibodies in the cells. Thus ANA testing is sometimes referred to as fluorescent antinuclear antibody test (FANA). Nowadays, a method to detect antinuclear antibodies called enzyme linked immunosorbent assay (ELISA) is replacing the previous method of immunofluorescent assay technique. The ELISA method is less likely to produce false positive ANA result than the previous method.
Patterns also give doctors a clue as to the type of illness to look for while evaluating a patient. For instance, the disease Scleroderma shows in nucleolar pattern. If a person does not have any autoimmune disease, it is defined in speckled pattern. An ANA blood test is used in patients who might be suffering from Sjogren's syndrome, rheumatoid arthritis, polymyositis, scleroderma, Hashimoto's thyroiditis, juvenile diabetes mellitus, Addison's disease, vitiligo, pernicious anemia, glomerulonephritis and pulmonary fibrosis. ANA can also be found in patients with conditions that are not considered autoimmune diseases such as chronic infections and cancer.
The result of the ANA test is expressed in titers. A titer of 1 to 80 (1:80) means that antibodies could be last detected when 1 part of the blood sample was diluted by 80 parts of another liquid. Usually this other liquid is a diluted salt solution. A larger second number indicates that the antibodies are present in greater concentration. Therefore a titer of 1 to 320 indicated higher concentration of antibodies in the blood than a titer of 1 to 80. The normal values of ANA blood test is : Titer below 1: 20 or 1:40 depending on the test method used.
Positive ANA test result is suggestive of autoimmune disease. It can also mean that the patient has drug induced lupus. Some drugs and infections can also induce false positive ANA test results. Steroids can cause a false-negative result. Medications, especially antibiotics such as isoniazid, penicillin, and tetracycline, birth control pills, lithium and some diuretics such as chlorthalidone can interfere with the test and affect the accuracy of the ANA test result.
Bibliography / Reference
Collection of Pages - Last revised Date: March 18, 2019