Inflammatory myopathy, also known as idiopathic inflammatory myopathy (IIM), is disease featuring

muscle weakness Muscle weakness is a lack of muscle strength. Its causes are many and can be divided into conditions that have either true or perceived muscle weakness. True muscle weakness is a primary symptom of a variety of skeletal muscle diseases, includ ...

inflammation Inflammation (from ) is part of the biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. The five cardinal signs are heat, pain, redness, swelling, and loss of function (Latin ''calor'', '' ...

of muscles ( myositis), and in some types, muscle pain (

myalgia Myalgia or muscle pain is a painful sensation evolving from muscle tissue. It is a symptom of many diseases. The most common cause of acute myalgia is the overuse of a muscle or group of muscles; another likely cause is viral infection, espec ...

). The cause of much inflammatory myopathy is unknown (

idiopathic An idiopathic disease is any disease with an unknown cause or mechanism of apparent spontaneous origin. For some medical conditions, one or more causes are somewhat understood, but in a certain percentage of people with the condition, the cause ...

), and such cases are classified according to their

symptom Signs and symptoms are diagnostic indications of an illness, injury, or condition. Signs are objective and externally observable; symptoms are a person's reported subjective experiences. A sign for example may be a higher or lower temperature ...

s and signs,

electromyography Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph to produce a record called an electromyogram. An electromyo ...

MRI Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to generate pictures of the anatomy and the physiological processes inside the body. MRI scanners use strong magnetic fields, magnetic field gradients, and rad ...

, and laboratory findings. It can also be associated with underlying cancer. The main classes of idiopathic inflammatory myopathy are

polymyositis Polymyositis (PM) is a type of chronic inflammation of the muscles ( inflammatory myopathy) related to dermatomyositis and inclusion body myositis. Its name is derived . The inflammation of polymyositis is mainly found in the endomysial layer ...

(PM),

dermatomyositis Dermatomyositis (DM) is a Chronic condition, long-term inflammatory disorder, inflammatory Autoimmune disease, autoimmune disorder which affects the skin and the muscles. Its symptoms are generally a skin rash and worsening muscle weakness over ...

(DM) (including juvenile, amyopathic, and sine-dermatitis form), inclusion-body myositis (IBM), immune-mediated necrotising myopathy (IMNM), and focal autoimmune myositis.

Diagnosis

Idiopathic inflammatory myopathy is a

diagnosis of exclusion A diagnosis of exclusion or by exclusion (''per exclusionem'') is a diagnosis of a medical condition reached by a process of elimination, which may be necessary if presence cannot be established with complete confidence from history, examination o ...

. There are a number of known causes of myopathy, and it is only once these have been ruled out that a clinician should assign an idiopathic inflammatory myopathy. The usual criteria for a diagnosis of PM are weakness in muscles of the head, neck, trunk, upper arms or upper legs; raised blood serum concentrations of some

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

s such as

creatine kinase Creatine kinase (CK), also known as creatine phosphokinase (CPK) or phosphocreatine kinase, is an enzyme () expressed by various tissues and cell types. CK catalyses the conversion of creatine and uses adenosine triphosphate (ATP) to create phos ...

; unhealthy muscle changes on

; and biopsy findings of (i)

muscle cell A muscle cell, also known as a myocyte, is a mature contractile Cell (biology), cell in the muscle of an animal. In humans and other vertebrates there are three types: skeletal muscle, skeletal, smooth muscle, smooth, and Cardiac muscle, cardiac ...

degeneration and regeneration and (ii) chronic inflammatory infiltrates in muscle cells. If heliotrope (purple) rash or Gottron's papules are also present, then the diagnosis is DM. In DM, myositis may not be clinically apparent but detectable via biopsy or

. If the criteria for PM are met but muscle weakness also affects the hands and feet or is not accompanied by pain IBM should be suspected, and confirmed when muscle cell biopsy reveals (i)

cytoplasm The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...

vacuole A vacuole () is a membrane-bound organelle which is present in Plant cell, plant and Fungus, fungal Cell (biology), cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water ...

s fringed by

basophilic Basophilic is a technical term used by pathologists. It describes the appearance of cells, tissues and cellular structures as seen through the microscope after a histological section has been stained with a basic dye. The most common such dye ...

granules and (ii) inflammatory infiltrate comprising mostly CD8 T lymphocytes and

macrophage Macrophages (; abbreviated MPhi, φ, MΦ or MP) are a type of white blood cell of the innate immune system that engulf and digest pathogens, such as cancer cells, microbes, cellular debris and foreign substances, which do not have proteins that ...

s; and electron microscopy reveals filamentous inclusions in both

and nucleus.

Treatment

There have been few randomized treatment trials, due to the relative rarity of inflammatory myopathies. The goal of treatment is improvement in

activities of daily living Activities of daily living (ADLs) is a term used in healthcare to refer to an individual's daily self-care activities. Health professionals often use a person's ability or inability to perform ADLs as a measure of their Performance status, functi ...

and muscle strength. Suppression of immune system activity (

immunosuppression Immunosuppression is a reduction of the activation or efficacy of the immune system. Some portions of the immune system itself have immunosuppressive effects on other parts of the immune system, and immunosuppression may occur as an adverse react ...

) is the treatment strategy. Patients with PM or DM almost always improve to some degree in response to treatment, at least initially, and many recover fully with maintenance therapy. (If there is no initial improvement from treatment of PM or DM, the diagnosis should be carefully re-examined.) There is no proven effective therapy for IBM, and most IBM patients will need assistive devices such as a cane, a walking frame or a wheelchair. The later in life IBM arises, the more aggressive it appears to be.

Polymyositis and dermatomyositis

In severe cases of PM and DM with systemic signs, an initial three to five days on intravenous

corticosteroid Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. Two main classes of corticosteroids, glucocorticoids and mineralocorticoids, are invo ...

( methylprednisolone) may be used; but normally treatment begins with a single daily (after breakfast) high dose of oral corticosteroid (

prednisone Prednisone is a glucocorticoid medication mostly used to immunosuppressive drug, suppress the immune system and decrease inflammation in conditions such as asthma, COPD, and rheumatologic diseases. It is also used to treat high blood calcium ...

). After a month or so the strength of every second day's dose is very gradually reduced over three to four months, to minimize the negative effects of the prednisone. When a high dose of prednisone cannot be reduced without losing muscle strength, or when prednisone is effective but it is producing significant complications, "steroid sparing" oral

immunosuppressant Immunosuppressive drugs, also known as immunosuppressive agents, immunosuppressants and antirejection medications, are drugs that inhibit or prevent the activity of the immune system. Classification Immunosuppressive drugs can be classified ...

s such as azathioprine, mycophenolate mofetil,

methotrexate Methotrexate, formerly known as amethopterin, is a chemotherapy agent and immunosuppressive drug, immune-system suppressant. It is used to treat cancer, autoimmune diseases, and ectopic pregnancy, ectopic pregnancies. Types of cancers it is u ...

and

cyclosporine Ciclosporin, also spelled cyclosporine and cyclosporin, is a calcineurin inhibitor, used as an immunosuppressant medication. It is taken orally or intravenously for rheumatoid arthritis, psoriasis, Crohn's disease, nephrotic syndrome, ecz ...

, may be used in combination with reduced prednisone. Some of these steroid sparing drugs can take several months to demonstrate an effect. To minimize side effects, patients on corticosteroids should follow a strict high-protein, low-carbohydrate, low-salt diet; and with long-term corticosteroid use a daily calcium supplement and weekly vitamin D supplement (and a weekly dose of Fosamax for postmenopausal women) should be considered. For patients not responding to this approach there is weak evidence supporting the use of intravenous

immunoglobulin An antibody (Ab) or immunoglobulin (Ig) is a large, Y-shaped protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as pathogenic bacteria, bacteria and viruses, includin ...

ciclosporin Ciclosporin, also spelled cyclosporine and cyclosporin, is a calcineurin inhibitor, used as an immunosuppressant medication. It is taken Oral administration, orally or intravenously for rheumatoid arthritis, psoriasis, Crohn's disease, nephr ...

tacrolimus Tacrolimus, sold under the brand name Prograf among others, is an immunosuppressive drug. After Allotransplantation, allogenic organ transplant, the risk of organ Transplant rejection, rejection is moderate. To lower the risk of organ rejectio ...

, mycophenolate mofetil and other agents; and trials of

rituximab Rituximab, sold under the brand name Rituxan among others, is a monoclonal antibody medication used to treat certain autoimmune diseases and types of cancer. It is used for non-Hodgkin lymphoma, chronic lymphocytic leukemia (in children and ad ...

have indicated a potential therapeutic effect.

Inclusion-body myositis

Despite its very similar clinical presentation to PM, IBM does not respond to the drugs that effectively treat PM, and there is no proven effective therapy for IBM. Alemtuzumab is being studied but as of May 2013 it had not demonstrated clinical effectiveness in IBM.

Dysphagia Dysphagia is difficulty in swallowing. Although classified under " symptoms and signs" in ICD-10, in some contexts it is classified as a condition in its own right. It may be a sensation that suggests difficulty in the passage of solids or l ...

(difficulty swallowing) may be improved by intravenous immunoglobulin, though more trials are needed. Non-fatiguing, systematic strength-building exercise has demonstrated benefit. Occupational and rehabilitation therapists can offer good advice on walking without falling and performing fine motor tasks, and can provide appropriate canes, braces and wheelchairs. Speech pathologists can provide advice on preventing choking episodes and reducing the anxiety of an immanent aspiration for both patients and carers.

Epidemiology

Every year between 2.18 and 7.7 people per million receive a diagnosis of PM or DM. Around 3.2 children per million per year are diagnosed with DM (termed juvenile dermatomyositis), with an average age of onset of seven years. Diagnosis of adult DM commonly occurs between 30 and 50 years of age. PM is an adult disease, usually emerging after the age of twenty. PM and DM are more common in females, more common in Caucasians, and least common in Asians. At any given time, about 35.5 people per million have IBM; it emerges after the age of 30 (usually after 50), and may be more common in males.

Differential diagnoses

Myositis (inflammation of the muscle) can be caused secondary to a number of primary diseases including: infection, muscle trauma, medications and toxins, inherited muscle diseases, and autoimmune disease such as

lupus Lupus, formally called systemic lupus erythematosus (SLE), is an autoimmune disease in which the body's immune system mistakenly attacks healthy tissue in many parts of the body. Symptoms vary among people and may be mild to severe. Common ...

. Other autoimmune diseases can mimic the symptoms of IMM (muscle weakness and autoantibodies), including Lambert–Eaton myasthenic syndrome,

myasthenia gravis Myasthenia gravis (MG) is a long-term neuromuscular junction disease that leads to varying degrees of skeletal muscle weakness. The most commonly affected muscles are those of the eyes, face, and swallowing. It can result in double vision, ...

, and the muscle form of

sarcoidosis Sarcoidosis (; also known as Besnier–Boeck–Schaumann disease) is a disease involving abnormal collections of White blood cell, inflammatory cells that form lumps known as granulomata. The disease usually begins in the lungs, skin, or lymph n ...

. Although idiopathic inflammatory myopathy (IIM) is a diagnosis of exclusion, it is often the initial misdiagnosis of several acquired non-inflammatory myopathies. This is due to a number of factors, including: * overlapping symptoms (such as muscle weakness, pain, elevated CK); * that delaying treatment for an inflammatory myopathy, in order to exclude potential non-inflammatory myopathies, may cause irreversible damage (although administering immunosuppressants and glucocorticosteroids to non-inflammatory myopathies may also cause damage); * that many of the testing methods for idiopathic inflammatory myopathy are non-specific (the same results could apply to many different myopathies); * and the unfamiliarity of the many rare diseases that are outside of rheumatology. Acquired non-inflammatory myopathies include toxin-induced myopathies, endocrine myopathies, metabolic myopathies, muscular dystrophies, congenital myasthenic syndrome, nutritional imbalances, and infection.

References

External links

{{Medical resources , DiseasesDB = 29473 , ICD10 = {{ICD10, M, 33, , m, 30, {{ICD10, G, 72, 4, g, 70 , ICD9 = {{ICD9, 359.6, {{ICD9, 710.3-{{ICD9, 710.4 , ICDO = , OMIM = , MedlinePlus = , eMedicineSubj = , eMedicineTopic = , MeshID = D009220 Systemic connective tissue disorders