Systemic-onset juvenile idiopathic arthritis (also known as systemic juvenile idiopathic arthritis (sJIA) or the juvenile onset form of Still's disease) is a type of juvenile idiopathic arthritis (JIA) with extra-articular manifestations like fever and rash apart from arthritis. It was originally called systemic-onset juvenile rheumatoid arthritis or Still's disease.

Predominantly extra-articular manifestations like high fevers, rheumatic rash, enlargement of the liver and spleen, enlargement of the lymph nodes, and anemia. Others manifestations include inflammation of the pleura, inflammation of the pericardium, inflammation of the heart's muscular tissue, and inflammation of the peritoneum are also seen.

It is sometimes called "juvenile-onset Still's disease", to distinguish it from adult-onset Still's disease. However, there is some evidence that the two conditions are closely related.

SLE may cause pericarditis - inflammation of the outer lining surrounding the heart, myocarditis - inflammation of the heart muscle, and/or endocarditis - inflammation of the inner lining of the heart. The endocarditis of SLE is non-infectious, and is also called (Libman–Sacks endocarditis). It involves either the mitral valve or the tricuspid valve. Atherosclerosis also occurs more often and advances more rapidly than in the general population.

SLE is one of several diseases known as "the great imitator" because it often mimics or is mistaken for other illnesses. SLE is a classical item in differential diagnosis, because SLE symptoms vary widely and come and go unpredictably. Diagnosis can thus be elusive, with some people having unexplained symptoms of SLE for years.

Common initial and chronic complaints include fever, malaise, joint pains, muscle pains, and fatigue. Because these symptoms are so often seen in association with other diseases, these signs and symptoms are not part of the diagnostic criteria for SLE. When occurring in conjunction with other signs and symptoms (see below), however, they are considered suggestive.

While SLE can occur in both males and females, it is found far more often in women, and the symptoms associated with each sex are different. Females tend to have a greater number of relapses, a low white blood cell count, more arthritis, Raynaud's phenomenon, and psychiatric symptoms. Males tend to have more seizures, kidney disease, serositis (inflammation of tissues lining the lungs and heart), skin problems, and peripheral neuropathy.

Systemic JIA is characterized by arthritis, fever, which typically is higher than the low-grade fever associated with polyarticular and a salmon pink rash. It accounts for 10-20% of JIA and affects males and females equally, unlike the other two subtypes of JIA, and affects adolescents. It generally involves both large and small joints. Systemic JIA can be challenging to diagnose because the fever and rash come and go. Fever can occur at the same time every day or twice a day (often in late afternoon or evening) with a spontaneous rapid return to baseline (vs. septic arthritis of continuous fever). The rash often occurs with fever. It is a discrete, salmon-pink macules of different sizes. It migrates to different locations on skin, rarely persisting in one location more than one hour. The rash is commonly seen on trunk and proximal extremities or over pressure areas.

Arthritis is often absent in the first weeks or even 6–8 months into the illness.

Systemic JIA may have internal organ involvement such as hepatosplenomegaly, lymphadenopathy, serositis, hepatitis, or tenosynovitis.

A polymorphism in macrophage migration inhibitory factor has been associated with this condition.

CREST syndrome (calcinosis, Raynaud's phenomenon, esophageal dysfunction, sclerodactyly, and telangiectasia) is associated with limited scleroderma. Other symptoms include:

Potential signs and symptoms include:

- Cardiovascular: Raynaud's phenomenon (is the presenting symptom in 30% of affected persons, occurs in 95% of affected individuals at some time during their illness); healed pitting ulcers on the fingertips; skin and mucousal telangiectasis; palpitations, irregular heart rate and fainting due to conduction abnormalities, hypertension and congestive heart failure.

- Digestive: gastroesophageal reflux disease, bloating, indigestion, loss of appetite, diarrhoea alternating with constipation, sicca syndrome and its complications, loosening of teeth and hoarseness (due to acid reflux).

- Pulmonary: progressive worsening of shortness of breath, chest pain (due to pulmonary artery hypertension) and dry, persistent cough due to interstitial lung disease.

- Musculoskeletal: joint, muscle aches, loss of joint range of motion, carpal tunnel syndrome and muscle weakness.

- Genitourinary: erectile dysfunction, dyspareunia, scleroderma renal crises and kidney failure.

- Other: facial pain due to trigeminal neuralgia, hand paresthesias, headache, stroke, fatigue, calcinosis and weight loss.

In the skin, systemic sclerosis causes hardening and scarring. The skin may appear tight, reddish, or scaly. Blood vessels may also be more visible. Where large areas are affected, fat and muscle wastage may weaken limbs and affect appearance. Patients report severe and recurrent itching of large skin areas. The severity of these symptoms varies greatly among patients: Some having scleroderma of only a limited area of the skin (such as the fingers) and little involvement of the underlying tissue, while others have progressive skin involvement. Digital ulcers — open wounds on especially on fingertips and less commonly the knuckles — are not uncommon.

These are also referred to as systemic autoimmune diseases. The autoimmune CTDs may have both genetic and environmental causes. Genetic factors may create a predisposition towards developing these autoimmune diseases. They are characterized as a group by the presence of spontaneous overactivity of the immune system that results in the production of extra antibodies into the circulation. The classic collagen vascular diseases have a "classic" presentation with typical findings that doctors can recognize during an examination. Each also has "classic" blood test abnormalities and abnormal antibody patterns. However, each of these diseases can evolve slowly or rapidly from very subtle abnormalities before demonstrating the classic features that help in the diagnosis. The classic collagen vascular diseases include:

- Systemic lupus erythematosus (SLE) – An inflammation of the connective tissues, SLE can afflict every organ system. It is up to nine times more common in women than men and strikes black women three times as often as white women. The condition is aggravated by sunlight.

- Rheumatoid arthritis – Rheumatoid arthritis is a systemic disorder in which immune cells attack and inflame the membrane around joints. It also can affect the heart, lungs, and eyes. Of the estimated 2.1 million Americans with rheumatoid arthritis, approximately 1.5 million (71 percent) are women.

- Scleroderma – an activation of immune cells that produces scar tissue in the skin, internal organs, and small blood vessels. It affects women three times more often than men overall, but increases to a rate 15 times greater for women during childbearing years, and appears to be more common among black women.

- Sjögren's syndrome – also called Sjögren's disease, is a chronic, slowly progressing inability to secrete saliva and tears. It can occur alone or with rheumatoid arthritis, scleroderma, or systemic lupus erythematosus. Nine out of 10 cases occur in women, most often at or around mid-life.

- Mixed connective tissue disease – Mixed connective-tissue disease (MCTD) is a disorder in which features of various connective-tissue diseases (CTDs) such as systemic lupus erythematosus (SLE); systemic sclerosis (SSc); dermatomyositis (DM); polymyositis (PM); anti-synthetase syndrome; and, occasionally, Sjögren syndrome can coexist and overlap. The course of the disease is chronic and usually milder than other CTDs. In most cases, MCTD is considered an intermediate stage of a disease that eventually becomes either SLE or Scleroderma.

- Undifferentiated connective tissue disease (UCTD) is a disease in which the body mistakenly attacks its own tissues. It is diagnosed when there is evidence of an existing autoimmune condition which does not meet the criteria for any specific autoimmune disease, such as systemic lupus erythematosus or scleroderma. Latent lupus and incomplete lupus are alternative terms that have been used to describe this condition.

- Psoriatic arthritis is also a collagen vascular disease.

The signs and symptoms of Kikuchi disease are fever, enlargement of the lymph nodes (lymphadenopathy), skin rashes, and headache. Rarely, enlargement of the liver and spleen and nervous system involvement resembling meningitis are seen. Often a bout of extreme fatigue can occur - often taking hold during latter parts of the day and the affected person can be more prone to fatigue from exercise.

Scleroderma is a group of autoimmune diseases that may result in changes to the skin, blood vessels, muscles, and internal organs. The disease can be either localized to the skin or involve other organs in addition to the skin. Symptoms may include areas of thickened skin, stiffness, feeling tired, and poor blood flow to the fingers or toes with cold exposure. One form of the condition, known as CREST syndrome, classically results in calcium deposits, Raynaud's syndrome, esophageal problems, thickening of the skin of the fingers and toes, and areas of small dilated blood vessels.

The cause is unknown. Risk factors include family history, certain genetic factors, and exposure to silica. The underlying mechanism involves the abnormal growth of connective tissue which is believed to occur as a result of the body's immune system attacking healthy tissues. Diagnosis is typically based on a person's symptoms and may be supported by a skin biopsy or blood tests.

While there is no cure, treatments may improve symptoms. Medications used include corticosteroids, methotrexate, and non-steroidal anti-inflammatory drugs (NSAIDs). Outcomes depend on the extent of disease. Those with localized disease generally have a normal life expectancy. In those with systemic disease typical life expectancy is about 11 years from onset. Death is often due to lung, gastrointestinal, or heart complications.

About 3 per 100,000 people develop the systemic form a year. The condition most often begins in middle age. Women are more often affected than men. Scleroderma was likely first described in 1753 by Carlo Curzio and then well documented in 1842. The term is from the Greek "sklerosis" meaning "hardness" and "derma" meaning "skin".

A connective tissue disease is any disease that has the connective tissues of the body as a target of pathology. Connective tissue is any type of biological tissue with an extensive extracellular matrix that supports, binds together, and protects organs. These tissues form a framework, or matrix, for the body, and are composed of two major structural protein molecules: collagen and elastin. There are many different types of collagen protein in each of the body's tissues. Elastin has the capability of stretching and returning to its original length—like a spring or rubber band. Elastin is the major component of ligaments (tissues that attach bone to bone) and skin. In patients with connective tissue disease, it is common for collagen and elastin to become injured by inflammation (ICT). Many connective tissue diseases feature abnormal immune system activity with inflammation in tissues as a result of an immune system that is directed against one's own body tissues (autoimmunity).

Diseases in which inflammation or weakness of collagen tends to occur are also referred to as collagen diseases. Collagen vascular diseases can be (but are not necessarily) associated with collagen and blood vessel abnormalities and that are autoimmune in nature. See also vasculitis.

Connective tissue diseases can have strong or weak inheritance risks, and can also be caused by environmental factors.

The three major types of JIA are oligoarticular, polyarticular, and systemic.

Kikuchi disease or Kikuchi-Fujimoto disease was described in 1972 in Japan. It is also known as histiocytic necrotizing lymphadenitis, Kikuchi necrotizing lymphadenitis, phagocytic necrotizing lymphadenitis, subacute necrotizing lymphadenitis, and necrotizing lymphadenitis.

It was first described by Dr Masahiro Kikuchi (1935–2012) in 1972 and independently by Y. Fujimoto.

Polyarticular JIA affects five or more joints in the first 6 months of disease. This subtype can include the neck and jaw, as well as the small joints usually affected. This type of JIA is more common in girls than in boys. It accounts for about 40% of JIA cases.

Usually, the smaller joints are affected in polyarticular JIA, such as the fingers and hands, although weight-bearing joints such as the knees, hips, and ankles may also be affected. The joints affected are usually symmetrical, meaning that it affects both joints on both sides of the body (such as both wrists.) Children with polyarticular JIA are also at risk for developing chronic iridocyclitis or uveitis and should also be monitored by an optometrist or ophthalmologist.

Rheumatoid factor may be positive, i.e. seropositive, in children with polyarticular JIA occurring between 9 and 16 years of age and is associated with" HLA DR4" and "HLA DW4". This group has poorer prognosis with about 50% progressing to severe disabiling arthritis, persisting into adulthood. It is generally seronegative in JIA occurring below 10 years of age with a milder disease process and responds better to treatment. Seropositivity is rare in children with systemic JIA. Due to the greater number of joints affected by polyarticular JIA, as well as the tendency to worsen over time, polyarticular JIA must be treated aggressively.

The hallmark symptom of SS is a generalized dryness, typically including dry mouth and keratoconjunctivitis sicca (dry eyes), part of what are known as sicca ("dryness") symptoms. Sicca syndrome also incorporates vaginal dryness and chronic bronchitis. SS may cause skin, nose, and vaginal dryness, and may affect other organs of the body, including the muscles (myositis), kidneys, blood vessels, lungs, liver, biliary system, pancreas, peripheral nervous system (distal axonal neuropathy or small fiber peripheral neuropathy) and brain. Some people have gastrointestinal or esophageal diseases such as GERD, achlorhydria or gastroparesis. Chronic pain with accompanying fatigue and brain fog may also occur.

Skin dryness in some people with SS may be the result of lymphocytic infiltration into skin glands. The symptoms may develop insidiously, with the diagnosis often not considered for several years, because the complaints of sicca may be otherwise attributed to medications, a dry environment, aging, or may be regarded as not of severity warranting the level of investigation necessary to establish the presence of the specific underlying autoimmune disorder.

SS can damage vital organs of the body with symptoms that may plateau or worsen, or go into remission as with other autoimmune diseases. Some people may experience only the mild symptoms of dry eyes and mouth, while others have symptoms of severe disease. Many patients can treat problems symptomatically. Others are forced to cope with blurred vision, constant eye discomfort, recurrent mouth infections, swollen parotid glands, dysphonia (vocal disorders including hoarseness), and difficulty in swallowing and eating. Debilitating fatigue and joint pain can seriously impair quality of life. Some patients can develop renal (kidney) involvement (autoimmune tubulointerstitial nephritis) leading to proteinuria (excess protein in urine), urinary concentrating defect, and distal renal tubular acidosis.

The presentation of amyloidosis is broad and depends on the site of amyloid accumulation. The kidney and heart are the most common organs involved.

Amyloid deposition in the kidneys can cause nephrotic syndrome, which results from a reduction in the kidney's ability to filter and hold on to proteins. The nephrotic syndrome occurs with or without elevations in creatinine and blood urea concentration, two biochemical markers of kidney injury. In AA amyloidosis, the kidneys are involved in 91–96% of people, symptoms ranging from protein in the urine to nephrotic syndrome and rarely renal insufficiency.

Amyloid deposition in the heart can cause both diastolic and systolic heart failure. EKG changes may be present, showing low voltage and conduction abnormalities like atrioventricular block or sinus node dysfunction. On echocardiography, the heart shows a restrictive filling pattern, with normal to mildly reduced systolic function. AA amyloidosis usually spares the heart.

People with amyloidosis do not get central nervous system involvement but can develop sensory and autonomic neuropathies. Sensory neuropathy develops in a symmetrical pattern and progresses in a distal to proximal manner. Autonomic neuropathy can present as orthostatic hypotension but may manifest more gradually with nonspecific gastrointestinal symptoms like constipation, nausea, or early satiety.

Accumulation of amyloids in the liver can lead to elevations in serum aminotransferases and alkaline phosphatase, two biomarkers of liver injury, which is seen in about one third of people. Liver enlargement is common. In contrast, spleen enlargement is rare, occurring in 5% of people. Splenic dysfunction, leading to the presence of Howell-Jolly bodies on blood smear, occurs in 24% of people with amyloidosis. Malabsorption is seen in 8.5% of AL amyloidosis and 2.4% of AA amyloidosis. One suggested mechanism for the observed malabsorption is that amyloid deposits in the tips of intestinal villi (fingerlike projections that increase the intestinal area available for absorption of food), begin to erode the functionality of the villi, presenting a sprue-like picture.

A rare development is a susceptibility to bleeding with bruising around the eyes, termed "raccoon-eyes," caused by amyloid deposition in the blood vessels and a reduced activity of thrombin and factor X, two clotting proteins that lose their function after binding with amyloid.

Amyloid deposits in tissue and causes enlargement of structures. Twenty percent of people with AL amyloidosis have an enlarged tongue, that can lead to obstructive sleep apnea, difficulty swallowing, and altered taste. Tongue enlargement does not occur in ATTR or AA amyloidosis. Enlarged shoulders, "shoulder pad sign," results from amyloid deposition in synovial space. Deposition of amyloid in the throat can cause hoarseness. Aβ2MG amyloidosis (Hemodialysis associated amyloidosis) likes to deposit in synovial tissue, causing chronic synovitis, which can lead to repeated carpal tunnel syndrome.

Both the thyroid and adrenal gland can be infiltrated. It is estimated that 10–20% of individuals with amyloidosis have hypothyroidism. Adrenal infiltration may be harder to appreciate given that its symptoms of orthostatic hypotension and low blood sodium concentration may be attributed to autonomic neuropathy and heart failure.

"Amyloid deposits occur in the pancreas of patients with diabetes mellitus, although it is not known if this is functionally important. The major component of pancreatic amyloid is a 37-amino acid residue peptide known as islet amyloid polypeptide or 'amylin.' This is stored with insulin in secretory granules in B cells and is co secreted with insulin." (Rang and Dale's Pharmacology, 2015.)

Sjögren syndrome (SjS, SS) is a long-term autoimmune disease in which the moisture-producing glands of the body are affected. This results primarily in the development of a dry mouth and dry eyes. Other symptoms can include dry skin, a chronic cough, vaginal dryness, numbness in the arms and legs, feeling tired, muscle and joint pains, and thyroid problems. Those affected are at an increased risk (5%) of lymphoma.

While the exact cause is unclear, it is believed to involve a combination of genetics and an environmental trigger such as exposure to a virus or bacteria. It can occur independently of other health problems (primary Sjögren syndrome) or as a result of another connective tissue disorder (secondary Sjögren syndrome). The inflammation that results progressively damages the glands. Diagnosis is by biopsy of moisture-producing glands and blood tests looking for specific antibodies. On biopsy there are typically lymphocytes within the glands.

Treatment is directed at the person's symptoms. For dry eyes artificial tears, medications to reduce inflammation, punctal plugs, or surgery to shut the tear ducts, may be tried. For a dry mouth, chewing gum (preferably sugar free), sipping water, or a saliva substitute may be used. In those with joint or muscle pain, ibuprofen may be used. Medications that can cause dryness, such as antihistamines, may also be stopped.

The disease was described in 1933 by Henrik Sjögren, after whom it is named; however, a number of earlier descriptions of people with the symptoms exist. Between 0.2% and 1.2% of the population are affected, with half having the primary form and half the secondary form. Females are affected about ten times as often as males and it commonly begins in middle age; however, anyone can be affected. Among those without other autoimmune disorders, life expectancy is unchanged.

An older clinical method of classification refers to amyloidoses as systemic or localised

- Systemic amyloidoses affect more than one body organ or system. Examples are AL, AA and Aβ2m.

- Localised amyloidoses affect only one body organ or tissue type. Examples are Aβ, IAPP, Atrial natriuretic factor (in isolated atrial amyloidosis), and Calcitonin (in medullary carcinoma of the thyroid)

Another classification is primary or secondary.

- Primary amyloidoses arise from a disease with disordered immune cell function, such as multiple myeloma or other immunocyte dyscrasias.

- Secondary (reactive) amyloidoses occur as a complication of some other chronic inflammatory or tissue-destroying disease. Examples are reactive systemic amyloidosis and secondary cutaneous amyloidosis.

Additionally, based on the tissues in which it is deposited, it is divided into mesenchymal (organs derived from mesoderm) or parenchymal (organs derived from ectoderm or endoderm).

Some people develop an initial "inflammatory phase" characterized by systemic illness with signs and symptoms of malaise, fever, night sweats, weight loss, joint pain, fatigue, and fainting. Fainting may result from subclavian steal syndrome or carotid sinus hypersensitivity. There is also often anemia and marked elevation of the ESR or C-reactive protein (nonspecific markers of inflammation). The initial "inflammatory phase" is often followed by a secondary "pulseless phase". The "pulseless phase" is characterized by vascular insufficiency from intimal narrowing of the vessels manifesting as arm or leg claudication, renal artery stenosis causing hypertension, and neurological manifestations due to decreased blood flow to the brain.

Of note is the function of renal artery stenosis in the causation of high blood pressure: Normally perfused kidneys produce a proportionate amount of a substance called renin. Stenosis of the renal arteries causes hypoperfusion (decreased blood flow) of the juxtaglomerular apparatus, resulting in exaggerated secretion of renin, and high blood levels of aldosterone, eventually leading to water and salt retention and high blood pressure. The neurological symptoms of the disease vary depending on the degree; the nature of the blood vessel obstruction; and can range from lightheadedness to seizures (in severe cases). One rare, important feature of the Takayasu's arteritis is ocular involvement in form of visual field defects, vision loss, or retinal hemorrhage. Some individuals with Takayasu's arteritis may present with only late vascular changes, without a preceding systemic illness. In the late stage, weakness of the arterial walls may give rise to localized aneurysms. As with all aneurysms, the possibility of rupture and vascular bleeding is existent and requires monitoring. In view of the chronic process and good collateral development, Raynaud's phenomenon or digital gangrene are very rare in Takayasu arteritis. A rare complication of this condition are coronary artery aneurysms.

Retinal vasculitis is very rare as the only presenting symptom. Often there is sufficient systemic evidence to help the physician decide between any one of the aforementioned possible systemic diseases. For those patients who present with only vasculitis of the retinal vessels, great investigative effort (Chest X-ray, blood test, urinary analysis, vascular biopsy, ophthalmology assessment, etc.) should be undertaken to ensure that a systemic disease is not the hidden culprit.

Autoimmunity is the system of immune responses of an organism against its own healthy cells and tissues. Any disease that results from such an aberrant immune response is termed an "autoimmune disease". Prominent examples include celiac disease, diabetes mellitus type 1, sarcoidosis, systemic lupus erythematosus (SLE), Sjögren's syndrome, eosinophilic granulomatosis with polyangiitis, Hashimoto's thyroiditis, Graves' disease, idiopathic thrombocytopenic purpura, Addison's disease, rheumatoid arthritis (RA), ankylosing spondylitis, polymyositis (PM), dermatomyositis (DM) and multiple sclerosis (MS). Autoimmune diseases are very often treated with steroids.

Ophthalmic examination may reveal neovascularization (creation of new vessels in the retina), retinal vessel narrowing, retinal vessel cuffing, retinal hemorrhage, or possible vitritis (inflammation of the vitreous body) or choroiditis (inflammation of the choroid).

Takayasu's arteritis (also known as Takayasu's disease, "aortic arch syndrome," "nonspecific aortoarteritis," and "pulseless disease") is a form of large vessel granulomatous vasculitis with massive intimal fibrosis and vascular narrowing, most commonly affecting often young or middle-age women of Asian descent, though anyone can be affected. It mainly affects the aorta (the main blood vessel leaving the heart) and its branches, as well as the pulmonary arteries. Females are about 8–9 times more likely to be affected than males.

Those with the disease often notice symptoms between 15 and 30 years of age. In the Western world, atherosclerosis is a more frequent cause of obstruction of the aortic arch vessels than Takayasu's arteritis. Takayasu's arteritis is similar to other forms of vasculitis, including giant cell arteritis which typically affects older individuals. Due to obstruction of the main branches of the aorta, including the left common carotid artery, the brachiocephalic artery, and the left subclavian artery, Takayasu's arteritis can present as pulseless upper extremities (arms, hands, and wrists with weak or absent pulses on the physical examination) which may be why it is also commonly referred to as the "pulseless disease." Involvement of renal arteries may lead to a presentation of renovascular hypertension.

Autoimmune diseases can be broadly divided into systemic and organ-specific or localised autoimmune disorders, depending on the principal clinico-pathologic features of each disease.

- Systemic autoimmune diseases include SLE, Sjögren's syndrome, sarcoidosis, scleroderma, rheumatoid arthritis, cryoglobulinemic vasculitis, and dermatomyositis. These conditions tend to be associated with autoantibodies to antigens which are not tissue specific. Thus although polymyositis is more or less tissue specific in presentation, it may be included in this group because the autoantigens are often ubiquitous t-RNA synthetases.

- Local syndromes which affect a specific organ or tissue:

- Endocrinologic: Diabetes mellitus type 1, Hashimoto's thyroiditis, Addison's disease

- Gastrointestinal: Coeliac disease, Crohn's disease, Pernicious anaemia

- Dermatologic: Pemphigus vulgaris, Vitiligo

- Haematologic: Autoimmune haemolytic anaemia, Idiopathic thrombocytopenic purpura

- Neurological: Multiple sclerosis, Myasthenia gravis, Encephalitis

Using the traditional “organ specific” and “non-organ specific” classification scheme, many diseases have been lumped together under the autoimmune disease umbrella. However, many chronic inflammatory human disorders lack the telltale associations of B and T cell driven immunopathology. In the last decade it has been firmly established that tissue "inflammation against self" does not necessarily rely on abnormal T and B cell responses.

This has led to the recent proposal that the spectrum of autoimmunity should be viewed along an “immunological disease continuum,” with classical autoimmune diseases at one extreme and diseases driven by the innate immune system at the other extreme. Within this scheme, the full spectrum of autoimmunity can be included. Many common human autoimmune diseases can be seen to have a substantial innate immune mediated immunopathology using this new scheme. This new classification scheme has implications for understanding disease mechanisms and for therapy development.

Autoimmune hepatitis, formerly called lupoid hepatitis, is a chronic, autoimmune disease of the liver that occurs when the body's immune system attacks liver cells causing the liver to be inflamed. Common initial symptoms include fatigue or muscle aches or signs of acute liver inflammation including fever, jaundice, and right upper quadrant abdominal pain. Individuals with autoimmune hepatitis often have no initial symptoms and the disease is detected by abnormal liver function tests.

Anomalous presentation of MHC class II receptors on the surface of liver cells, possibly due to genetic predisposition or acute liver infection, causes a cell-mediated immune response against the body's own liver, resulting in autoimmune hepatitis. This abnormal immune response results in inflammation of the liver, which can lead to further symptoms and complications such as fatigue and cirrhosis. The disease may occur in any ethnic group and at any age, but is most often diagnosed in patients between age 40 and 50.