Arthritis (from Greek arthro-, joint + -itis, inflammation; plural: arthritides) is a group of conditions involving damage to the joints of the body.

There are different forms of arthritis and each has a different cause. The most common form of arthritis, osteoarthritis (degenerative joint disease) is a result of trauma to the joint, infection of the joint, or age. Other arthritis forms are rheumatoid arthritis and psoriatic arthritis, autoimmune diseases in which the body attacks itself. Septic arthritis is caused by joint infection. Gouty arthritis is caused by deposition of uric acid crystals in the joint, causing inflammation. There is also an uncommon form of gout caused by the formation of rhomboid crystals of calcium pyrophosphate. This gout is known as pseudogout.

History and physical examination

All arthritides feature pain. Pain patterns may differ depending on the arthritides and the location. Rheumatoid arthritis is generally worse in the morning and associated with stiffness; in the early stages, patients often have no symptoms after a morning shower. In the aged and children, pain might not be the main presenting feature; the aged patient simply moves less, the infantile patient refuses to use the affected limb.

Elements of the history of the disorder guide diagnosis. Important features are speed and time of onset, pattern of joint involvement, symmetry of symptoms, early morning stiffness, tenderness, gelling or locking with inactivity, aggravating and relieving factors, and other systemic symptoms. Physical examination may confirm the diagnosis, or may indicate systemic disease. Radiographs are often used to follow progression or assess severity in a more quantitative manner.

Blood tests and X-rays of the affected joints often are performed to make the diagnosis. Screening blood tests are indicated if certain arthritides are suspected. These might include: rheumatoid factor, antinuclear factor (ANF), extractable nuclear antigen, and specific antibodies.

Types of arthritis

Primary forms of arthritis:

• Osteoarthritis
• Rheumatoid arthritis
• Septic arthritis
• Gout and pseudogout
• Juvenile idiopathic arthritis
• Still's disease
• Ankylosing spondylitis

Secondary to other diseases:

• Lupus erythematosus
• Sarcoidosis
• Henoch-Schönlein purpura
• Psoriatic arthritis
• Reactive arthritis
• Haemochromatosis
• Hepatitis
• Wegener's granulomatosis (and many other vasculitis syndromes)
• Lyme disease
• Familial Mediterranean fever
• Hyperimmunoglobulinemia D with recurrent fever
• TNF receptor associated periodic syndrome
• Inflammatory bowel disease (Including Crohn's Disease and Ulcerative Colitis)

Diseases that can mimic arthritis include:

• Hypertrophic osteoarthropathy
• Multiple myeloma
• Osteoporosis
• Fifth disease (parvovirus infection)