Fusion, which may be fibrous, or bony (as in ankylosing spondylitis)


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

Axial Spondyloarthritis (axSpA)

A form of spondyloarthritis in which the predominant symptom is back pain, and where radiographic (evident on X-ray) sacroiliitis might or might not be present

Biologic Response Modifiers

Called biologicals/biologics for short are any medicinal products manufactured in or extracted from biological sources. They include TNF-a blockers such as infliximab (Remicade), adalimumab (Humira), etanercept (Enbrel), golimumab (Simponi), and certolizumab pegol (Cimzia).

C-Reactive Protein (CRP)

Its measurement in the blood can be used to detect or grade inflammation


A small protein released by cells that has a specific effect on the interactions between cells, on communications between cells, or on the behavior of cells.

The cytokines includes the interleukins, lymphokines and cell signal molecules, such as tumor necrosis factor and the interferons, which trigger inflammation and respond to infections.


Site of attachment of ligament or tendon to bone


Inflammation of an enthesis

Erythrocyte Sedimentation Rate (ESR)

A blood test commonly used to detect or grade inflammation

Genetic Marker

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


A word in common use to describe the large and small intestine

Human Leucocyte Antigens (HLA)

Cell surface proteins, detected by blood testing, that vary from person to person; also called tissue antigens because ideally organ donors and recipients must have compatible HLA, otherwise the transplanted organ is recognized as foreign and is rejected

Related to the workings of the immune system; present self and 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

Consist of two broad types, called class I and class II HLA


An HLA class I molecule that has been assigned the number 27

Quite a few HLA antigens confer susceptibility to certain diseases: HLA-B27 to AS, and HLA-DR4 to rheumatoid arthritis, for example.


Of unknown cause or explanation

Inflammatory Bowel Disease

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


Forward stooping (bowing) of the spine

Monoclonal Antibodies

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

Non-radiographic Axial Spondyloarthritis (nr-axSpA)

Form of axial spondyloarthritis in which X-ray changes are not present, but clinical symptoms may occur

During this time, up to 70% of patients may have visible inflammation in the sacroiliac joints and/or the spine on MRI.

NSAID (Nonsteroidal Anti-inflammatory Drug)

Non-cortisone, non-addictive (non-narcotic) drugs that reduce pain and inflammation and are therefore used in the treatment of pain and arthritis

Patient Registry

An organized system that uses observational study methods to collect uniform data (clinical and other) to evaluate specified outcomes for a population defined by a particular disease, condition, or exposure, and that serves a predetermined scientific, clinical, or policy purpose(s)


Inflammation in many joints; conventionally in more than four joints


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

Range of Motion

The extent to which a joint is able to go through all of its normal movements

Range of motion exercises help increase or maintain flexibility and movement in muscles, tendons, ligaments, and joints.


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

Sacroiliac Joints

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

Spondyloarthritis and Spondyloarthropathy (SpA)

Umbrella under which AS and related diseases are grouped

These diseases show clinical similarities and occur much more often in people who carry the HLA-B27 gene.

The diseases in this grouping are:

  • Ankylosing spondylitis
  • Reactive arthritis
  • Psoriatic arthritis
  • Juvenile spondyloarthritis
  • Enteropathic arthritis (spondylitis/arthritis associated with inflammatory bowel disease)
  • Undifferentiated spondyloarthritis

Sausage Digit

Finger or toe that is diffusely swollen; usually seen in psoriatic and reactive arthritis; also called “dactylitis”

Tumor Necrosis Factor-alpha (TNF-α)

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; attaches to a cell surface protein called TNF receptor to exert its effect on the cell

TNF-α Blockers

Biologic medications that block the action of TNF-α and can reduce inflammation

Stay Informed

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