Polymyositis (PM) is a type of chronic

inflammation Inflammation (from la, wikt:en:inflammatio#Latin, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or Irritation, irritants, and is a protective response involving im ...

of the

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

s (

inflammatory myopathy Inflammatory myopathy is disease featuring weakness and inflammation of muscles and (in some types) muscle pain. The cause of much inflammatory myopathy is unknown (idiopathic), and such cases are classified according to their symptoms and signs ...

) related to

dermatomyositis Dermatomyositis (DM) is a long-term inflammatory disorder which affects skin and the muscles. Its symptoms are generally a skin rash and worsening muscle weakness over time. These may occur suddenly or develop over months. Other symptoms may inc ...

and

inclusion body myositis Inclusion body myositis (IBM) () (sometimes called sporadic inclusion body myositis, sIBM) is the most common inflammatory muscle disease in older adults. The disease is characterized by slowly progressive weakness and wasting of both proximal ...

. Its name means "inflammation of many muscles" ('' poly-'' + '' myos-'' + ''

-itis Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells, blood vessels, and molec ...

''). The inflammation of polymyositis is mainly found in the endomysial layer of

skeletal muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

, whereas dermatomyositis is characterized primarily by inflammation of the perimysial layer of skeletal muscles.

Signs and symptoms

The hallmark of polymyositis is weakness and/or loss of muscle mass in the proximal musculature, as well as flexion of the neck and torso. These symptoms can be associated with marked pain in these areas as well. The

hip extensors In anatomy, extension is a movement of a joint that increases the angle between two bones or body surfaces at a joint. Extension usually results in straightening of the bones or body surfaces involved. For example, extension is produced by extendin ...

are often severely affected, leading to particular difficulty in climbing stairs and rising from a seated position. The skin involvement of dermatomyositis is absent in polymyositis.

Dysphagia Dysphagia is difficulty in swallowing. Although classified under "symptoms and signs" in ICD-10, in some contexts it is classified as a disease#Terminology, condition in its own right. It may be a sensation that suggests difficulty in the passag ...

(difficulty swallowing) or other problems with esophageal

motility Motility is the ability of an organism to move independently, using metabolic energy. Definitions Motility, the ability of an organism to move independently, using metabolic energy, can be contrasted with sessility, the state of organisms th ...

occur in as many as 1/3 of patients. Low grade fever and

enlarged lymph nodes Lymphadenopathy or adenopathy is a disease of the lymph nodes, in which they are abnormal in size or consistency. Lymphadenopathy of an inflammatory type (the most common type) is lymphadenitis, producing swollen or enlarged lymph nodes. In cl ...

may be present.

Foot drop Foot drop is a gait abnormality in which the dropping of the forefoot happens due to weakness, irritation or damage to the deep fibular nerve (deep peroneal), including the sciatic nerve, or paralysis of the muscles in the anterior portion of t ...

in one or both feet can be a symptom of advanced polymyositis and

. The systemic involvement of polymyositis includes

interstitial lung disease Interstitial lung disease (ILD), or diffuse parenchymal lung disease (DPLD), is a group of respiratory diseases affecting the interstitium (the tissue and space around the alveoli (air sacs)) of the lungs. It concerns alveolar epithelium, pu ...

(ILD) and heart disease, such as

heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, a ...

and conduction abnormalities. Polymyositis tends to become evident in adulthood, presenting with bilateral proximal muscle weakness often noted in the upper legs due to early fatigue while walking. Sometimes the weakness presents itself as an inability to rise from a seated position without help or an inability to raise one's arms above one's head. The weakness is generally progressive, accompanied by lymphocytic inflammation (mainly

cytotoxic T cell A cytotoxic T cell (also known as TC, cytotoxic T lymphocyte, CTL, T-killer cell, cytolytic T cell, CD8+ T-cell or killer T cell) is a T lymphocyte (a type of white blood cell) that kills cancer cells, cells that are infected by intracellular pa ...

s).

Associated illnesses

Polymyositis and the associated inflammatory myopathies have an associated increased risk of

cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...

. The features they found associated with an increased risk of cancer were older age, age greater than 45, male sex,

difficulty swallowing 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 liqui ...

death Death is the irreversible cessation of all biological functions that sustain an organism. For organisms with a brain, death can also be defined as the irreversible cessation of functioning of the whole brain, including brainstem, and brain ...

of skin cells, cutaneous vasculitis, rapid onset of myositis (<4 weeks), elevated

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 pho ...

, higher

erythrocyte sedimentation rate The erythrocyte sedimentation rate (ESR or sed rate) is the rate at which red blood cells in anticoagulated whole blood descend in a standardized tube over a period of one hour. It is a common hematology test, and is a non-specific measure of ...

and higher

C-reactive protein C-reactive protein (CRP) is an annular (ring-shaped) pentameric protein found in blood plasma, whose circulating concentrations rise in response to inflammation. It is an acute-phase protein of hepatic origin that increases following interleukin- ...

levels. Several factors were associated with lower-than-average risk, including the presence of interstitial lung disease, joint inflammation/

joint pain Arthralgia (from Greek ''arthro-'', joint + ''-algos'', pain) literally means ''joint pain''. Specifically, arthralgia is a symptom of injury, infection, illness (in particular arthritis), or an allergic reaction to medication. According to MeSH, ...

Raynaud's syndrome Raynaud syndrome, also known as Raynaud's phenomenon, eponymously named after the physician Auguste Gabriel Maurice Raynaud, who first described it in his doctoral thesis in 1862, is a medical condition in which the spasm of small arteries cau ...

, or anti-Jo-1 antibody. The malignancies that are associated are

nasopharyngeal cancer Nasopharyngeal carcinoma (NPC), or nasopharynx cancer, is the most common cancer originating in the nasopharynx, most commonly in the postero-lateral nasopharynx or pharyngeal recess ( fossa of Rosenmüller), accounting for 50% of cases. NPC occurs ...

lung cancer Lung cancer, also known as lung carcinoma (since about 98–99% of all lung cancers are carcinomas), is a malignant lung tumor characterized by uncontrolled cell growth in tissue (biology), tissues of the lung. Lung carcinomas derive from tran ...

non-Hodgkin's lymphoma Non-Hodgkin lymphoma (NHL), also known as non-Hodgkin's lymphoma, is a group of hematological malignancy, blood cancers that includes all types of lymphomas except Hodgkin lymphomas. Symptoms include lymphadenopathy, enlarged lymph nodes, fever ...

and

bladder cancer Bladder cancer is any of several types of cancer arising from the tissues of the urinary bladder. Symptoms include blood in the urine, pain with urination, and low back pain. It is caused when epithelial cells that line the bladder become mali ...

, amongst others. Cardiac involvement manifests itself typically as heart failure and is present in up to 77% of patients. Interstitial lung disease is found in up to 65% of patients with polymyositis, as defined by HRCT or restrictive ventilatory defects compatible with interstitial lung disease.

Causes

Polymyositis is an inflammatory myopathy mediated by cytotoxic T cells with an as yet unknown

autoantigen In immunology, autoimmunity is the system of immune responses of an organism against its own healthy cells, tissues and other normal body constituents. Any disease resulting from this type of immune response is termed an "autoimmune disease". P ...

, while dermatomyositis is a humorally mediated

angiopathy Angiopathy is the generic term for a disease of the blood vessels (arteries, veins, and capillaries). The best known and most prevalent angiopathy is diabetic angiopathy, a common complication of chronic diabetes. Classification By caliber Ther ...

resulting in myositis and a typical dermatitis. The cause of polymyositis is unknown and may involve viruses and autoimmune factors. Cancer may trigger polymyositis and dermatomyositis, possibly through an immune reaction against cancer that also attacks a component of muscles. There is tentative evidence of an association with

celiac disease Coeliac disease (British English) or celiac disease (American English) is a long-term autoimmune disorder, primarily affecting the small intestine, where individuals develop intolerance to gluten, present in foods such as wheat, rye and barl ...

Diagnosis

Diagnosis is fourfold: History and physical examination, elevation of

, electromyograph (EMG) alteration, and a positive

muscle biopsy In medicine, a muscle biopsy is a procedure in which a piece of muscle tissue is removed from an organism and examined microscopically. A muscle biopsy can lead to the discovery of problems with the nervous system, connective tissue, vascular s ...

. The hallmark clinical feature of polymyositis is proximal muscle weakness, with less important findings being muscle pain and dysphagia. Cardiac and pulmonary findings will be present in approximately 25% of cases of patients with polymyositis. Sporadic

(sIBM) is often misdiagnosed as polymyositis or dermatomyositis but it can be differentiated as myositis that does not respond to treatment is likely IBM. sIBM comes on over months to years; polymyositis comes on over weeks to months. Polymyositis tends to respond well to treatment, at least initially; IBM does not.

Treatment

The first line treatment for polymyositis is corticosteroids. Specialized exercise therapy may supplement treatment to enhance quality of life.

Epidemiology

Polymyositis strikes females with greater frequency than males.

Polymyositis as a distinct diagnosis

The discovery of several myositis-specific autoantibodies during the past decades has enabled the description of other discrete subsets of diagnosis, specifically the discovery of Antisynthetase syndrome in reducing the number of diagnoses of polymyositis.

Society and culture

Notable cases

Dan Christensen Dan Christensen, (October 6, 1942 – January 20, 2007) was an American abstract painter He is best known for paintings that relate to Lyrical Abstraction, Color field painting, and Abstract expressionism. Christensen was born in Cozad ...

, painter of abstract art. Died due to

caused by polymyositis. *

Robert Erickson Robert Erickson (March 7, 1917 – April 24, 1997) was an American composer. Education Erickson was born in Marquette, Michigan. He studied with Ernst Krenek from 1936 to 1947: "I had already studied—and abandoned—the twelve tone sy ...

, American composer and teacher who was a leading modernist exponent of "12-tone" composition. Died from the effects of polymyositis. *

David Lean Sir David Lean (25 March 190816 April 1991) was an English film director, producer, screenwriter and editor. Widely considered one of the most important figures in British cinema, Lean directed the large-scale epics ''The Bridge on the River ...

, film director. *

Eric Samuelsen Eric Roy Samuelsen (April 10, 1956 – September 20, 2019) was an American playwright and emeritus professor of theatre at Brigham Young University in Provo, Utah. He is considered one of the most important Mormon playwrights, and has been cal ...

, playwright. * Victor Manuel Resendiz Ruiz, wrestler. * Cardinal John Wright

References

External links

{{Systemic connective tissue disorders Inflammations Steroid-responsive inflammatory conditions Systemic connective tissue disorders