Achilles tendinitis: Inflammation of the Achilles tendon, causing swelling and tenderness at the lower end of the calf where it inserts into the heel bone.

Acupuncture: An ancient medical procedure that originated in China more than 2000 years ago. It is based on the theoretical concept of balanced Qi (pronounced 'chee') or vital energy that flows throughout the body via certain pathways that are accessed by puncturing the skin with hair-thin needles at particular locations called acupuncture points. Stimulation of acupuncture points is believed to stimulate the brain and spinal cord to release chemicals that change the experience of pain or cause biochemical changes that may stimulate healing and promote general well-being. See also alternative and complementary remedies; traditional Chinese medicine.

Allele: Alternate forms of a gene at a distinct location (locus) on a chromosome.

Alternative and complementary remedies: These include holistic medicine, folk remedies, and alternative therapies (herbal medications or extracts, homeopathy, Ayurvedics, and traditional Chinese medicine (TCM). These complementary and alternative treatments are mostly based on anecdotal evidence, primarily from individuals who report their own successful use of the treatment. One needs to apply scientific methods to establish the validity of the anecdotal evidence.

Amino acids: Small organic molecules which are the building blocks of peptides and proteins.

Amyloid: A proteinaceous fibrillar material deposited in various tissues and organs, sometimes secondary to a chronic inflammatory disease.

Analgesia: Pain relief, e.g. by such drugs as paracetamol, NSAIDs or narcotics. These pain-relieving drugs are called analgesics (see NSAIDs).

Ankylosing hyperostosis: Also called Forestier's disease or diffuse idiopathic skeletal hyperostosis (DISH). It causes excessive new bone formation along the spine and other sites (at entheses), can result in stiff spine that may be confused with AS.

Ankylosing spondylitis (AS): An inflammatory arthritic disorder, primarily of the axial skeleton (sacroiliac joints and spine), but can affect hip and shoulder joints and infrequently the peripheral joints. It causes chronic back pain and leads to stiffness of the spine. Most of the affected individuals have the HLA-B27 gene.

Ankylosis: Fusion, which may be fibrous, or bony (as in AS).

Annulus fibrosus: The tough outer fibrous layer of the intervertebral disc.

Antibodies: Proteins produced by white blood cells (plasma cells and B lymphocytes) that confer immunity.

Antigen: A substance that causes the body's immune system to produce antibodies that try to eliminate it because the body sees the antigen as foreign or harmful substance (e.g. from invading viruses or bacteria).

Antigen-presenting cell: A cell that ingests and processes foreign substance (e.g. from invading viruses or bacteria) and displays the resulting antigen fragments (small peptides) on its surface to activate those T cells that respond specifically to that antigen.

Aortitis: Inflammation of the aorta, which is the main artery that carries the blood from the heart to ultimately supply the needs of the body.

Arachnoiditis: Fibrosis (scarring) of the membrane covering the spinal cord and spinal nerve roots as they pass through the spinal canal. This results in entrapment of these nerve roots that may cause chronic back and leg pain and neurological dysfunction. It can occur following spinal surgery, and has also been associated in the past with the use of an X-ray contrast medium. Very rarely it can occur in the lower end of the spinal canal in AS without any apparent reason, and is the cause of cauda equina syndrome in this disease.

Arthralgia: Pain in one or more joints without any outward evidence of a joint abnormality.

Arthritis: Literally means inflammation of the joint, and is used to refer to more than 100 joint diseases, some of which may also affect other regions of the body. The plural is arthritides.

Arthritis mutilans: An extremely destructive form of arthritis; the term is usually applied to a very severe form of psoriatic arthritis.

Arthrocentesis: Taking a sample of joint fluid out for testing, obtained by a needle puncture of the joint. Sometimes all of the joint fluid may be aspirated as a part of treatment.

Arthrodesis: A surgically induced or spontaneous fusion of a joint.

Arthroplasty: Surgical procedure to alter a joint, e.g. its excision and replacement by an artificial joint.

Arthroscopy: Inspection of the inside of a joint, e.g. for obtaining a biopsy, usually through a fiber optic instrument called arthroscope.

Autoimmune disease: A disease in which the immune system attacks and destroys the body's own tissues that it mistakenly believes to be foreign.

Axial arthritis: Arthritis in the spine and/or neighboring joints, especially the sacroiliac joints, as in AS, in contrast to arthritis of peripheral (limb) joints.

Ayurveda: The traditional Indian medical system, which claims that health is based on a harmonious relationship between three humors called 'doshas', and disharmony results in disease.

B cells (B lymphocytes): Antibody-producing white blood cells, which mature in the bone marrow. The letter B originally came from bursa of Fabricius where B lymphocytes originate in chickens, but has subsequently been extended to imply the bone marrow.

Bamboo spine: X-ray appearance of spine in advanced AS because of spinal fusion producing a bamboo-like appearance

Biologic response modifiers: Drugs which are also called biologicals for short, and include anti-TNF drugs infliximab (Remicade) and etanercept (Enbrel).

Biopsy: Removal of a small tissue specimen for examination.

Bisphosphonates: Drugs used to treat osteoporosis because they inhibit bone resorption.

Bowel: A word commonly used for the small and large intestines (see gut, large intestine, small intestine).

Brand name: The brand name (trademark) of a drug is coined by the manufacturer in agreement with the regulating agencies, unlike the generic name which indicates its active ingredients. For example, celecoxib is the generic name for the drug whose brand name is Celebrex. The brand name starts with a capital letter but the generic name does not. Several brand name drugs can have the same generic name if they contain the same active ingredient. Thus, Motrin and Aleve are both brand names for the generic drug ibuprofen.

Bursa: A fluid-filled sac found between tissue planes over bony places subject to shearing forces, as over the elbow and knee. It is lined by synovium that secretes the lubricating fluid.

Bursitis: An inflammation of a bursa.

Calcification: Deposition of chalky (calcific) material in tissue, leading to bone formation.

Campylobacter: A type of bacteria. Enteric infections with these bacteria can trigger reactive arthritis in susceptible individuals

Capsule: A thick membrane joining together ends of two adjacent bones to form a joint. Its inside is lined with synovium that forms the joint fluid.

Cartilage: A tissue that covers the ends of bones to form a smooth shock-absorbing surface for joints, and results in very low friction movement. Cartilage also occurs at other sites, such as the nose and the ears.

Cauda equina syndrome: Some people with advanced AS on rare occasions may get this neurological condition resulting from gradual scarring at the lower end of the spine that entraps the lower spinal nerves. The name cauda equina means horsetail, so named because the lowermost spinal nerves slope downward as a bunch before they exit the vertebral column.

CD4+ (CD8+) T lymphocytes: These T cells carry a marker on the surface known as a cluster of differentiation (CD) marker which can be either CD4 or COB. The CD4+ T cells, also known as helper T cells, help orchestrate the antibody responses, and the CDB+ T cells-also called cytotoxic (destructive to cells) or suppressor T cells-are involved in cell-mediated immunity that targets infected cells.

Celiac disease: inability to digest and absorb a protein found in wheat, resulting in poor absorption of nutrients from the foods because of damage to the lining of the small intestine; also called gluten intolerance or non-tropical sprue.

Cervicitis: Inflammation of the cervix, the part of the uterus that protrudes into the vagina.

Chromosome: A thread-like structure within the nucleus of a cell that contains the genes. There are 46 chromosomes in the nucleus of a human cell; 22 of them are in pairs that are given the numbers 1-22, and the remaining two are the X or Y chromosomes (sex chromosomes) that determine a person's sex-males have one X and one Y chromosomes, and females have two X chromosomes.

Chlamydia trachomatis: A bacterium that has a predilection to infect the genitourinary tract. Such an infection is the more commonly recognized initiator of reactive arthritis in the United States.

Clostridium difficile: Bacteria that are normally present in the large intestine, can cause a serious illness called pseudo-membranous colitis in people taking antibiotics, and can sometimes trigger reactive arthritis.

Collagen and connective tissue: A set of fibrous proteins and supporting framework that form the main building blocks of the body, including the internal organs, ligaments, tendon, cartilage, bone, and skin.

Conjunctivitis: Commonly known as pink eye; it is an inflammation of the delicate outer membrane that lines the inside of the eyelids and the white of the eye.

Contracture: Arthritis or prolonged immobility can result in the involved joint becoming less freely moveable. Associated with shortening and wasting of muscles.

Control group: In clinical studies the control.group, which is given either the standard treatment for a medical condition under study or an inactive substance (called a placebo), is compared with a group given an experimental treatment to find its efficacy for the disease under study.

Coping: The psychological processes following any stressful situation.

Cortisone: A natural hormone made by the adrenal gland. Sometimes wrongly used as a synonym for corticosteroids.

Corticosteroids: A group of related compounds which, like cortisone, reduce inflammation and irritation caused by many disease processes, including many forms of arthritis, and skin and bowel diseases.

Crohn's disease: A chronic inflammatory bowel disease (also called ileitis or regional enteritis), that can affect the entire gastrointestinal tract, though it usually involves the lower small intestine, (the ileum) and the adjacent part of the colon.

C-reactive protein (CRP): Its measurement in the blood can be used to detect or grade inflammation.

Cytokine: A soluble protein, produced by white blood cells, that acts as a messenger between cells, either stimulating or inhibiting the activity of various cells of the immune system. There is normally a very delicate balance among the various cytokines.

Cytoplasm: A liquid compartment in the cell, surrounding the central nucleus. The cytoplasm contains mitochondria and other structures or components responsible for normal protein formation, secretion and other cell functions.

DEXA bone scan: A means of measuring the bone density to detect osteoporosis at a much earlier stage as compared to a standard X-ray. DEXA stands for dualenergy X-ray absorption i.e. X-ray absorption at two different quantum energies or wavelengths.

Disorder: A synonym for disease.

Disability: In the context of health experience, a disability is a restriction or lack (resulting from an impairment) of ability to perform an activity in the manner or within the range considered normal.

Distal: Farther away from the trunk. For example, a hand is the distal end of an arm. The opposite is proximal.

DNA: A double-stranded, helical molecule that carries genetic information, primarily present within the nucleus of each cell in plants and animals. It tells the cells exactly what to do and how to perform their functions.

Double-blinded: A doubled-blinded trial produces more objective and unbiased results because neither the research investigators nor the study participants know who is receiving the investigational drug and who is receiving the placebo

Duodenum: The first part of the small intestine. An ulcer on its inner lining is called a duodenal ulcer.

Dowager's hump: A hump in the upper back (thoracic kyphosis) in an elderly woman with osteoporosis.

Dysentery: An infectious disease of the intestine that causes bloody, mucus-filled diarrhea, which can be accompanied by abdominal pain or cramps, fever, and dehydration from excessive diarrhea. It is caused by enteric infections, usually with Shigella, and can sometimes trigger reactive arthritis.

Elimination diet: Requirement that certain foods should not be eaten.

Enteritis: An inflammation (irritation) of the small intestine.

Enthesis: Site of attachment of ligament or tendon to bone.

Enthesitis: Inflammation of an enthesis.

Enthesopathy: An all-inclusive term that covers all abnormalities of an enthesis (e.g. enthesitis is an inflammatory type of enthesopathy).

Enzyme: A protein that acts to promote or facilitate certain biochemical processes in the body; e.g. many enzymes produced in the gut assist in digestion of food.

Epicondylitis: Enthesopathy at bony prominence (epicondyle) of the elbow; may occur on the medial (inner) side (golfer's elbow) or the lateral (outer) side (tennis elbow).

Erythrocyte sedimentation rate (ESR): A blood test commonly used to detect or grade inflammation.

Esophagus: The tube-like passage through which swallowed food travels from the mouth to the stomach.

Familial: A term used to indicate a disease or a trait (an inherited characteristic) which tends to affect more than one member in a family.

Fascia: Tough membrane that encloses muscles and other organs.

Fasciitis: Inflammation of the fascia.

Fibromyalgia: A complex chronic painful condition, primarily occurring in women, characterized by widespread musculoskeletal pain, and fatigue, and accompanied by tender points at defined locations, often associated with a non-restorative sleep pattern.

Fibrositis: A term used interchangeably with fibromyalgia.

Folic acid: and Folinic acid: Members of the vitamin B complex.

Food poisoning: An acute food-borne gastrointestinal infection caused by food contaminated by harmful bacteria that results in symptoms such as diarrhea, abdominal discomfort or cramps, and fever.

Forestier's disease: See ankylosing hyperostosis.

Gastric ulcer: An ulcer on the inner lining of the stomach.

Gastrointestinal tract: Alimentary tract, including esophagus, stomach, duodenum, ileum, large bowel, and rectum.

Gene: Part of the DNA molecule responsible for making proteins. It is the basic unit ofhereditYi all information in the genes (genetic information) is passed from parent to child.

Generic name: See brand name.

Genetic counseling: Informing people about genetic facts that may guide them in making a decision based on a knowledge of disease risk. The word genetic refers to any characteristic that is inherited.

Genetic marker: A gene that is used to identify an individual disease or trait, or trace its inheritance within a family.

Genitourinary tract: The genitalia, the bladder, and the urethral tube through which the bladder empties.

Gut: A word in common use to describe the large and small intestine (see bowel, large intestine, small intestine).

Handicap: In the context of health experience, a handicap is a disadvantage for a given individual, resulting from an impairment or a disability, that limits or prevents the fulfillment of a role that is normal (depending on age, sex, and social and cultural factors) for that individual.

H2~blockers: Medicines such as cimetidine (Tagamet), ranitidine (Zantac), or famotidine (Pepcid), used to treat acid indigestion, heartburn, and ulcer pain. They are so called because they act by blocking histamine-2 signals to reduce the amount of acid produced by the stomach.

Heartburn: Symptoms caused by stomach acid flowing back into the esophagus.

Helicobacter pylori: A corkscrew-shaped bacterium found in the stomach that can predispose to stomach and duodenal ulcers. Previously called Campylobacter pylori.

Heterozygote and homoozygote: An individual inherits a set of two alleles for each HLA locus from his or her parents. For instance, an individual may inherit HLAB27 from one parent and HLA-B8 from the other. Most individuals do not inherit the same gene (belonging to a locus) from both parents, and are said to be heterozygotes. Someone who inherits the same gene, e.g. HLA-B27, from both parents is homozygous for HLA-B27.

HLA: Human leucocyte antigens. These are cell surface proteins, detected by blood testing, that vary from person to person. They are also called tissue antigens or histocompatibility antigens because ideally organ donors and recipients must have compatible HLA; otherwise the transplanted organ is recognized as nonself ('foreign') and is rejected. HLA are related to the workings of the immune system; they present selfand foreign-derived (e.g. viral) peptides (a few amino acids linked together) to T lymphocytes and other cells of the immune system that help the body fight illness. They are of two broad types, called class I and class II HLA. Their genes are located on chromosome 6; the loci are given the letters A, B, C, D, and so on.

HLA-B27: An HLA class I molecule that has been assigned the number 27; its gene is present at the B locus. There are quite a few HLA antigens that confer susceptibility to certain diseases: HLA-B27 to AS, and HLA-DR4 to rheumatoid arthritis, for example.

Hydrotherapy: Physiotherapy in a pool (usually heated).

Idiopathic: Of unknown cause or explanation.

Ileum: The major part of the small intestine (see small intestine).

Ilium (or iliac bone): Major bony component of the pelvis. There is one on each side, joined to the sacrum via the right and left sacroiliac joints.

Impairment: In the context of health experience, an impairment is any loss or abnormality of psychological, physiological or anatomical structure or function (WHO, 1980).

Incidence: The rate of occurrence of some event, such as the number of individuals who get a disease divided by a total given population, per unit of time (usually per year). In contrast to prevalence, incidence describes the number of new cases of a disease among a certain group of people for a certain period of time, i.e. how often a new case is diagnosed.

Inflammation: A typical reaction of tissues to injury or disease, usually marked by four signs: pain, swelling, redness, and heat. It may be acute (as in a bum or in gouty arthritis) or chronic (as in rheumatoid arthritis or chronic infections such as tuberculosis).

Inflammatory bowel disease: A chronic (long-lasting) inflammatory disease of the gut, e.g. ulcerative colitis or Crohn's disease.

Internist: A doctor specializing in internal medicine (not requiring surgery).

Intestine: Also called bowel or gut (see large intestine; small intestine).

Intestinal flora: Bacteria and other organisms that normally grow in the intestine.

Intestinal mucosa: Surface lining of the intestines where the absorption of nuttients takes place.

Intra-articular: Into or within a joint, e.g. intra-articular injection.

Joint: The place where two bones meet. Most joints are composed of cartilage, joint space, fibrous capsule, joint lining (synovium) and ligaments.

Juvenile chronic arthritis (aka juvenile spondyloarthropathy): Arthritis in children 16 years of age or less, that has been present for at least 3 months, and for which no other cause is obvious. It is now preferably called juvenile idiopathic arthritis.

Keratoderma blennorrhagica: Rash on palms of the hands and soles of the feet which may occur in reactive arthritis (Reiter's syndrome); it resembles a form of psoriasis.

Kyphosis: Forward stooping (bowing) of the spine ('humpback' deformity).

Large intestine: Part of the intestine that changes stool from a liquid to a solid form by absorbing water. Often simply called the colon, but in fact includes the appendix, cecum, colon, and rectum; has a total length of about 5 feet (1.5 m).

Leukocyte: White blood cell, part of the immune system.

Ligament: Stretchy tough band of cord-like tissue that connects bones together, and confers stability by restraining excessive joint movement.

Limb girdle joints: Hip and shoulder joints.

Locus: Precise location of a gene on a chromosome.

Lymphocyte: A type of white blood cell present in the blood, lymph and lymphoid tissues; primarily responsible for immune responses (see also B lymphocytes; CD4+ (CD8+) T lymphocytes; T lymphocytes).

Macrophage: A relatively large immune system cell that devours invading bacteria and other intruders, and stimulates other immune cells by presenting them with small pieces of the invaders. Can sometimes harbor large quantities of invading viruses like HIV without being killed, and thus act as a reservoir of such viruses.

Magnetic resonance imaging (MRI): A method of taking pictures of the soft tissues in the body that are clearer than those obtained by X-rays, and without radiation.

Medial: On the inside (as opposed to lateral); not to be confused with the median nerve which is compressed in carpal tunnel syndrome.

Methotrexate: A drug which is used in low doses for the treatment of inflammatory disorders, including various types of inflammatory arthritis, and in very high doses to treat certain cancers. It is sometimes abbreviated to MTX (See also slow-acting anti-rheumatic drugs).

Monoclonal antibodies: Artificially produced antibodies used in research and also for treatment of some diseases. They are produced in a cell culture (clone) by multiplying one single mother cell thus having exactly the same properties (very pure antibody).

MRI: See magnetic resonance imaging.

Nucleus: The central controlling structure within a living cell that contains the genetic codes (in chromosomes) for maintaining life systems of the cell and for issuing commands for cell growth and reproduction.

Nausea: The feeling of wanting to throw up (vomit).

Neurohormones: Biochemical substances made by tissue in the body's nervous system that can change the function or structure, or direct the activity of tissues or organs; e.g. neurotransmitters.

Neurological: Relating to the body's nervous system, which oversees and controls all body functions.

Neurotransmitters: Biochemical substances that stimulate or inhibit nerve impulses in the brain that relay information about external stimuli and sensations, such as pain.

NK (natural killer) cells: Non-specific lymphocytes like killer T cells that attack and kill cancer and infected cells. They are natural killers because they do not need to recognize a specific antigen in order to attack and kill.

NSAID (nonsteroidal anti-inflammatory drug): Noncortisone, non-addictive (non-narcotic) drug that reduces pain and inflammation and is therefore used in the treatment of pain and arthritis.

Oligoarthritis: Inflammation of up to four joints; if more joints are involved, then the disease is called poly, arthritis.

Onycholysis: Nail abnormality and discoloration seen in psoriasis and reactive arthritis; may be accompanied by pitting of the nail in psoriasis.

Osgood-Schlatter's disease: A childhood condition of the site of attachment of the patellar (kneecap) tendon into the tibial tubercle, a bony prominence an inch or so below the kneecap. Results in localized pain and tenderness that can sometimes be confused with enthesitis at this site seen in some children with juvenile AS and related diseases.

Osteitis condensans ilii: Increased bone density (sclerosis) at the sacral side of the sacroiliac joint that is of unknown cause and is usually without symptoms. Its X-ray appearance can be confused with sacroiliitis.

Osteoarthritis (osteoarthrosis): Degenerative disorder of joints, most often from disease in the spine and in the weight bearing joints (knees and hips). Normally seen with aging, but can occur prematurely due to various reasons, for instance after an injury to a joint. Also known as degenerative joint disease, it can cause joint pain, loss of function, reduced joint motion, and deformity.

Osteomalacia: Bone-thinning disorder resulting from deficiency of vitamin D. Can be mistaken for osteoporosis, and can also be confused with spondylitis. The childhood form of osteomalacia is called rickets.

Osteophyte: Bony outgrowth (seen on X-ray) at joint margin of an osteoarthritic joint, or in degenerative disc disease.

Osteoporosis; A disease characterized by reduction in mineral content usually seen with aging, but also in connection with certain conditions such as paralysis, or due to prolonged use of certain drugs, such as corticosteroids.

Paget's disease: A disease characterized by accelerated bone turnover, resulting in the involved bone becoming enlarged but weak and fragile. The bone also feels warmer to touch due to increased blood supply. Also called osteitis deformans.

Pathogenesis: Process of development of a disease.

Pauciarthritis: same as oligoarthritis.

Pelvis: The bony structures in the lowest part of the trunk. The term pelvic is used for anything that belongs or refers to the pelvis.

Peptic ulcer: A sore in the lining of the stomach (gastric ulcer) or duodenum (duodenal ulcer). The word peptic refers to the stomach and the duodenum, where pepsin is present, an enzyme that breaks down proteins. An ulcer can sometimes occur in the lower part of the esophagus in association with heartburn.

Peptide: A few amino acids linked together. Proteins are made of multiple pep tides linked together.

Placebo: Originally a Latin word meaning 'I will please'. Now used for inactive substance (sham) given to participants of a research study in order to test the efficacy of another substance or treatment. In shortterm clinical trials, many of the most valued drugs in clinical use are only about 25% more effective than placebo. Scientists often have to compare the effects of active and inactive substances to learn more about how the active substance affects participants; in such studies both doctor and patient are unaware of who is receiving the active or inactive substance. Such studies are known as double blind placebo controlled studies.

Polyarthralgia: Pains in many joints; conventionally refers to more than four joints, without signs of inflammation in the symptomatic joints.

Polyarthritis: Inflammation in many joints; conventionally in more than four joints.

Preclinical diagnosis; Diagnosis of a genetic disease before there are any symptoms or signs.

Prevalence: The observed number of people in a given population affected with a particular disease or condition at a given time, usually stated as the number of cases observed per 100 000 individuals, or listed as a percentage. In contrast with incidence, prevalence can be thought of as a snapshot of all existing cases at a specified time.

Prognosis: The probable end result or outcome of a disease.

Protein: A large molecule composed of amino acids. Essential components of the body tissue (see also peptide).

Proton pump inhibitors: A group of drugs used to treat heartburn and peptic ulcer disease. These include omprezole (Prilosec), esomeprazole (Nexium) and pansoprazole (Prevacid).

Prospective, randomized, double blind: Study clinical trial or study in which the method of data analysis is specified in a protocol before the study is begun (prospective). Patients are randomly assigned to receive either the study drug or an alternative treatment, and neither the patient nor the doctor conducting the study knows which treatment is being given to which patient (see also placebo).

Proximal: The part of a limb that is closest to the trunk. For example, the shoulder joint forms the proximal end of the upper extremity (opposite of distal).

Psoriasis: A common chronic skin disease, more common in whites (2% of the population) than in other racial groups, in which red flaky lesions occuroften on the elbows and knees, or in the scalp. May cause nail abnormalities.

Psoriatic arthritis: Arthritis associated with psoriasis; occurs in more than 10% of people with psoriasis. May occur in several forms, including a form associated with spinal involvement (psoriatic spondylitis).

Qi: Chinese term for vital energy or life force. Pronounced chee (see acupuncture).

Radiography/radiograph/radiogram/radiologic: Radiography (or roentgenography) is the method of taking a picture with the help of X-rays, and the terms radiograph or simply X-ray are sometimes used for the resulting picture. Radiogram is the correct name for an image taken by radiography.

Randomized, double-blind, placebo-controlled, multicenter trial: A clinical trial in which patients have been randomly assigned to receive either the study drug or the alternative treatment under study. Neither the patient nor the doctor conducting the study knows which treatment is being given; the alternative to the study drug is a placebo; and the study is conducted at several centers.

Range of motion: The extent to which a joint is able to go through all of its normal movements. Range-ofmotion exercises help increase or maintain flexibility and movement in muscles, tendons, ligaments, and joints.

Reactive arthritis: Arthritis resulting from infection elsewhere in the body; i.e. there is no infection in the joint. The most common type is HLA B27-related and may follow certain types of bowel or genitourinary infection.

Reiter's syndrome: A form of HLA B27-related reactive arthritis with a classical triad of arthritis, conjunctivitis, and urethritis, with or without other features of spondyloarthropathies. The term reactive arthritis is now used more commonly to describe this condition.

Rheumatic fever: A form of reactive arthritis triggered by streptococcal sore throat. Its features include very painful joint inflammation (arthritis). It is now uncommon in developed countries but still occurs commonly in other parts of the world. It can cause inflammation and scarring of heart valvos (rheumatic heart disease).

Rheumatoid arthritis: A chronic systemic disease that causes inflammatory changes in the synovium, or joint lining, that result in pain, stiffness, swelling, and ultimately loss of function and deformities of the affected joints due to destruction of the cartilage and adjacent bone. The disease can also affect other parts of the body. In the past it was also called chronic polyarthritis. It is more common in women than men, and at least 70% of patients show a positive blood test for rheumatoid factor.

Rheumatologist: A doctor (board-certified internist or pediatrician) who has had specialized training in diagnosing and treating disorders that affect the joints, muscles, tendons, ligaments, connective tissue, and bones.

Roentgenography: See radiography.

Sacroiliac joints: Two joints, one on either side, in the lower back, between the two pelvic bones called sacrum and ilium.

Sacroiliitis: Inflammation of the sacroiliac joint; bilateral sacroiliitis is a hallmark of AS.

Sacrum: Major bony component of the pelvis, shaped like a wedge on which the spine rests. It forms a joint with ilium, one on each side, via the right and left sacroiliac joints

Salmonella: A group of bacteria comprising many different types that may cause intestinal infection and diarrhea called salmonellosis, which includes typhoid fever. Enteric infections with Salmonella, Shigella, Yersinia, or Campylobacrer are the most common triggers for reactive arthritis, especially in some developing parts of the world.

SAPHO syndrome: So named because of its salient features: synovitis, acne, palmoplantar pustulosis, hyperostosis, aseptic osteomyelitis. This rare disease causes aseptic (no evidence of infection) bone necrosis at multiple sites that can include the sacroiliac joints or the spine. It is known by many different names, but SAPHO syndrome is the most common.

Sausage digit: Finger or toe that is diffusely swollen as a result of tenosynovitis; usually seen in psoriatic and reactive arthritis. It is also called dactylitis.

Scheuermann's disease: A non-inflammatory spinal disease that occurs in adolescence and affects the thoracic spine, especially the discs. Often painless, but can result in a stooped back.

Schober's test: To detect the ability to bend forward (flexibility) of the lumbar spine (see Figure 5g and accompanying caption).

Scoliosis: A non-inflammatory rotational deformity of the spine; results in a lateral curvature.

Selective estrogen receptor modulators (SERM): A class of drugs used in the treatment of osteoporosis; they mimic the effect of estrogen but in a tissueselective manner.

Septic arthritis: Bacterial infection of one or more joints; requires urgent diagnosis and treatment.

Seronegative arthritis: An arthritis that is not associated with the presence of an autoantibody called rheumatoid factor in the blood. Most people with AS and related spondyloarthopathies lack this autoantibody, and therefore these diseases are examples of seronegative arthritis. On the other hand, only about 25% of people with rheumatoid arthritis are seronegative.

Shigella: A group of bacteria that can cause an illness called shigellosis, with high fever and acute diarrhea, sometimes mixed with blood (dysentery). Enteric infections with Shigella can trigger reactive arthritis.

Sibling: Brother or sister.

Skeletal muscles: Muscles that move the bony skeleton, i.e. provide movement at the joints.

Slit lamp: An instrument used by eye specialists (opthalmologists) to look for inflammation or other diseases inside the eye.

Slow-acting and symptom-modifying anti-rheumatic drugs (SAARDS and SMARDs): Drugs such as sulfasalazine and methotrexate, which may be useful in spondyloarthropathies that are resistant to conventional therapy. Any benefit from these drugs takes some time to manifest itself, hence the name. Unlike NSAlDs, these drugs are not pain relievers, but they will help relieve pain if they can first heal or control the underlying inflammation.

Small intestine: The tubular organ, about 20 feet (6 m) long, where most digestion occurs. It is made up of three parts: the duodenum (which is attached to the stomach), jejunum, and ileum (which ends in the large intestine).

Spondylitis: Literally means inflammation of the spine, and is best exemplified by ankylosing spondylitis (AS).

Spondyloarthritis and spondyloarthopathy: AS and related diseases are grouped under this term. These diseases show clinical similarities to some extent, and occur much more often in people who carry the HLAB27 gene.

Spondylolisthesis: A loss of spinal column alignment that results from one vertebra slipping forward on top of another.

Spondylosis: Non-inflammatory degenerative (wear and tear) disease of the spinal column as we get older, such as degenerative disc disease

Steroids: see corticosteroids.

Stomach ulcer: An open sore in the lining of the stomach. also called gastric ulcer.

Sulfasalazine: See slow-acting anti-rheumatic drugs.

Syndesmophytes: Ligamentous bone deposits (ossification) producing fine bony bridging between adjacent vertebral bodies at the margin of the vertebrae, characteristic of AS. They are vertically orientated, unlike osteophytes (seen in degenerative disc disease), which grow horizontally.

Syndrome: A complex of signs and symptoms that when occurring together suggest a particular disease.

Synovium: A thin membrane (normally one or two cell layers thick) lining the inside of the joint capsule. It produces synovial fluid for lubrication and nourishment of the joint cartilage.

Synovitis: Inflammation of the joints resulting from inflamed synoviumj this results in joint inflammation (arthritis).

T cell (or T lymphocyte): T stands for the thymus, where T lymphocytes mature. T cells are white blood cells that playa critical role in immune response, but, unlike B lymphocytes, do not produce antibodies (immunoglobulins). There are two main subtypes: the CD4+ helper T cells and the CD8+ cytotoxic or suppressor T cells.

Tai Chi: A traditional Chinese mind-body relaxation exercise consisting of 108 intricate exercise sequences performed in a slow relaxed manner over a 30 minute period.

Temporo-mandibular joint (TMJ): The jaw joint.

Tendon: A tough cord or band of fibrous tissue by which muscles are attached to bone.

Tendinitis (tendonitis): Inflammation of a tendon.

TENS (transcutaneous electrical nerve stimulation): A type of therapy used to relieve pain that involves passing electricity to nerve cells through electrodes placed on the skin.

TNF (tumor necrosis factor alpha): A cytokine (messenger protein) that plays a key role in the body's immune response by promoting inflammation, controlling the production of other pro-inflammatory molecules, and also helping the cells heal or repair themselves. It attaches to a cell surface protein called TNF receptor to exert its effect on the cell.

Traditional Chinese medicine (TCM): An ancient Chinese system of medicine, that includes meditation, herbal and nutritional therapy, restorative physical exercises and massage, and acupuncture. (See also acupuncture; alternative healthcare and complementary remedies).

Urethritis: An inflammatory condition of the urethra (the tube through which the urine travels from the bladder to the outside during urination).

Ulcer: A sore on the skin surface or on the inside lining of a body part, such as the mouth or stomach.

Ulcerative colitis: An inflammatory disease of the inner lining of the gut that usually involves the colon or rectum. (See also inflammatory bowel disease).

Yersinia: A group of bacteria comprising many different types that may cause intestinal infection and diarrhea. Enteric infections with Yersinia, Salmonella, Shigella, or Campylobacter are the most common triggers for reactive arthritis.