Polymyositis
Encyclopedia
Polymyositis("inflammation of many muscles") is a type of chronic inflammation of the muscles (inflammatory myopathy
Inflammatory myopathy
Inflammatory myopathy is a form of myopathy that involves inflammation of the muscle.Inflammatory myopathy is generally synonymous to the term dermatopolymyositis, which, according to ICD-10 encompasses three related diseases: polymyositis, dermatomyositis, and inclusion-body...

) related to dermatomyositis
Dermatomyositis
Dermatomyositis is a connective-tissue disease related to polymyositis and Bramaticosis that is characterized by inflammation of the muscles and the skin.- Causes :...

 and inclusion body myositis
Inclusion body myositis
Inclusion body myositis is an inflammatory muscle disease, characterized by slowly progressive weakness and wasting of both distal and proximal muscles, most apparent in the muscles of the arms and legs...

.

Signs and symptoms

Symptoms include pain, with marked weakness and/or loss of muscle mass in the proximal musculature, particularly in the shoulder and pelvic girdle. The hip extensors are often severely affected, leading to particular difficulty in ascending stairs and rising from a seated position. Thickening of the skin on the fingers and hands (sclerodactyly) is a frequent feature, although this is non-specific and occurs in other autoimmune connective tissue disorders. Dysphagia (difficulty swallowing) and/or other aspects of oesophageal dysmotility occur in as many as 1/3 of patients. Low grade fever and peripheral adenopathy may be present. Foot drop
Foot drop
Foot drop is the dropping of the forefoot due to weakness, damage to the peroneal nerve or paralysis of the muscles in the anterior portion of the lower leg. It is usually a symptom of a greater problem, not a disease in itself. It is characterized by the inability or difficulty in moving the ankle...

 in one or both feet can be a symptom of advanced Polymyositis and inclusion body myositis
Inclusion body myositis
Inclusion body myositis is an inflammatory muscle disease, characterized by slowly progressive weakness and wasting of both distal and proximal muscles, most apparent in the muscles of the arms and legs...

. Polymyositis is also associated with interstitial lung diseases.

Polymyositis is linked to an increase in the occurrence of certain cancers (particularly Non-Hodgkin lymphoma, lung and bladder cancers), but the overall association is weaker than in the related condition Dermatomyositis
Dermatomyositis
Dermatomyositis is a connective-tissue disease related to polymyositis and Bramaticosis that is characterized by inflammation of the muscles and the skin.- Causes :...

. The latter is linked to a significant increase in the risk of a variety of malignances, including ovarian, lung, and pancreatic cancer.

Polymyositis tends to become evident in adulthood, presenting with bilateral proximal muscle weakness often noted in the upper legs due to early fatigue
Fatigue (physical)
Fatigue is a state of awareness describing a range of afflictions, usually associated with physical and/or mental weakness, though varying from a general state of lethargy to a specific work-induced burning sensation within one's muscles...

 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 lymphocytes).

Polymyositis, like dermatomyositis, strikes females with greater frequency than males. The skin involvement of dermatomyositis is absent in polymyositis.

Another concern is Interstitial lung disease (ILD).

Causes

The etiology of polymyositis is unknown and may be multifactorial, perhaps related to autoimmune factors, genetics
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....

, and viruses. In rare cases, the cause is known to be infectious, associated with the pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...

s that cause Lyme disease
Lyme disease
Lyme disease, or Lyme borreliosis, is an emerging infectious disease caused by at least three species of bacteria belonging to the genus Borrelia. Borrelia burgdorferi sensu stricto is the main cause of Lyme disease in the United States, whereas Borrelia afzelii and Borrelia garinii cause most...

, toxoplasmosis
Toxoplasmosis
Toxoplasmosis is a parasitic disease caused by the protozoan Toxoplasma gondii. The parasite infects most genera of warm-blooded animals, including humans, but the primary host is the felid family. Animals are infected by eating infected meat, by ingestion of feces of a cat that has itself...

, and other infectious agents. Polymyositis usually is considered non-fatal in the absence of ILD.

It is hypothesized that an initial injury causes release of muscle auto antigen, which is subsequently taken up by macrophages and presented to CD4+ TH cells. Activated TH cells synthesize IFN-γ that stimulate further macrophages and further inflammatory mediator release like IL-1
IL-1
IL-1 may refer to:* Interleukin 1, a protein* Illinois' 1st congressional district* Illinois Route 1* Building 1 of Infinite Loop , the Headquarters of Apple Inc....

 and TNF-α

Another important event in the pathogenesis of Polymyositis is the increased expression of MHC
Major histocompatibility complex
Major histocompatibility complex is a cell surface molecule encoded by a large gene family in all vertebrates. MHC molecules mediate interactions of leukocytes, also called white blood cells , which are immune cells, with other leukocytes or body cells...

 proteins by m/s cells. Auto-Ag is presented in association with MHC-I molecules on the surface of Myocytes and is recognized by CD8 cytotoxic T cells that subsequently initiate m/s destruction.

Diagnosis

Diagnosis
Diagnosis
Diagnosis is the identification of the nature and cause of anything. Diagnosis is used in many different disciplines with variations in the use of logics, analytics, and experience to determine the cause and effect relationships...

 is fourfold, including elevation of creatine kinase
Creatine kinase
Creatine kinase , also known as creatine phosphokinase or phospho-creatine kinase , is an enzyme expressed by various tissues and cell types. CK catalyses the conversion of creatine and consumes adenosine triphosphate to create phosphocreatine and adenosine diphosphate...

, history and physical examination, electromyograph (EMG) alteration, and a positive muscle biopsy
Biopsy
A biopsy is a medical test involving sampling of cells or tissues for examination. It is the medical removal of tissue from a living subject to determine the presence or extent of a disease. The tissue is generally examined under a microscope by a pathologist, and can also be analyzed chemically...

.

Sporadic inclusion body myositis
Inclusion body myositis
Inclusion body myositis is an inflammatory muscle disease, characterized by slowly progressive weakness and wasting of both distal and proximal muscles, most apparent in the muscles of the arms and legs...

 (sIBM): IBM is often confused with (misdiagnosed as) polymyositis and dermatomyositis that does not respond to treatment is likely IBM. sIBM comes on over months to years; polymyositis comes on over weeks to months. It appears that sIBM and polymyositis share some common features, especially the initial sequence of immune system activation; however, polymyositis does not display the subsequent muscle degeneration and protein abnormalities as seen in IBM. As well, polymyositis tends to respond well to treatments; IBM does not. IBM and polymyositis apparently involve different disease mechanisms than are seen in dermatomyositis
Dermatomyositis
Dermatomyositis is a connective-tissue disease related to polymyositis and Bramaticosis that is characterized by inflammation of the muscles and the skin.- Causes :...

.

Laboratory findings

Presence of Anti Jo antibodies in >65% of patients. Elevated serum creatine kinase
Creatine kinase
Creatine kinase , also known as creatine phosphokinase or phospho-creatine kinase , is an enzyme expressed by various tissues and cell types. CK catalyses the conversion of creatine and consumes adenosine triphosphate to create phosphocreatine and adenosine diphosphate...

 is characteristic, but not specific to polymyositis.

Anti-signal recognition particle antibodies (anti-SRP antibodies) are associated with polymyositis, but are not very specific for it. For individuals with polymyositis, the presence of anti-SRP antibodies are associated with more prominent muscle weakness and atrophy.

Treatment

Typically, high-dose steroids are the treatment of choice. Generally, muscle strength will improve within 4–6 weeks (useful to distinguish from inclusion body myositis). Unresponsive patients may be tried on other immunosuppressive medications. IVIG has also shown to be a beneficial treatment. Specialized exercise therapy
Exercise therapy for idiopathic inflammatory myopathies
Although they vary in particulars, polymyositis, dermatomyositis and inclusion body myositis are idiopathic inflammatory myopathies primarily characterized by chronic inflammation of human skeletal muscle tissue that ultimately causes the necrosis of muscle cells. This degeneration leads to...

may supplement treatment to enhance quality of life.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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