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The most important crystal arthropathy is
caused by deposition of uric acid, causing true gout.
Urate gout is characterized by deposition of urate crystals in joints and soft
tissues, which is caused by the presence of hyperuricaemia. Uric acid is
normally derived from the breakdown of purines and is excreted in the urine.
Urate gout is largely confined to men, although some women develop it after the
menopause. It can present at any time between the ages 20 and 60 years, most
cases presenting with an acute attack of arthritis, often affecting the big toe.
There are two main reasons for hyperuricaemia:
• Underexcretion of uric acid.} Seen in the majority of patients with urate
gout, but of uncertain origin. It is clinically associated with hyperlipidaemia,
renal failure, alcohol consumption, and some drugs (diuretics).
• Overproduction of uric acid.} High-cell turnover (leukaemia and chemotherapy
for tumours). Rare congenital enzyme defects of purine metabolism.
In the majority of patients with urate gout, disease is probably the result of
polygenic factors leading to underexcretion of uric acid (primary gout). Only a
small proportion of patients develop urate gout as a result of overproduction of
Urate crystals are deposited in certain joints, particularly the
metatarsophalangeal joint of the big toe, stimulating an acute inflammatory
reaction leading to a painful acute arthritis. Uric acid crystals are also
deposited in the soft tissues around joints, where their presence excites a
foreign-body giant-cell reaction. These soft tissue masses may enlarge to
produce a palpable mass composed of white chalky material (tophi).
In the joint the urate crystals are deposited on the surface of the articular
cartilage to form a white powdery deposit, beneath which the cartilage shows
degenerative changes. Attacks of acute gouty arthritis are intermittent and may
be precipitated by dietary indiscretion.
Urate crystals deposited in the kidney may lead to an interstitial nephritis and
to renal calculi composed of uric acid. Precipitation of urates in renal tubules
may produce acute tubular necrosis and acute renal failure in leukaemic patients
with massive purine release after chemotherapy.
Hyperuricaemic gout has a familial tendency and is believed to be polygenically
inherited. It is associated with an increased predisposition to hypertension and
coronary artery disease.
Infective arthritis is mainly due to pyogenic bacteria and mycobacteria
Pyogenic bacteria may gain access to a joint either by bloodstream spread or,
more commonly, by local trauma or spread from adjacent infective foci. Infective
arthritis is a well-recognized complication of prosthetic surgery at the knee
and hip (the most common sites for infective arthritis of all types and causes).
A wide range of bacteria may be responsible, but Staphylococcus aureus,
streptococci and Haemophilus are the most important. Blood-borne infection by
the gonococcus is an important cause in teenagers and young adults.
Tuberculous arthritis is now rare, and is the result of bloodstream spread from
pulmonary TB. In adults the vertebral column is most often affected; tuberculous
osteomyelitis leads to collapse of affected vertebrae, particularly in the
lumbar and lower thoracic spine (Pott's disease), and paravertebral collection
of tuberculous caseous material occasionally tracks down the psoas muscle (psoas
abscess) to point in the groin. In children, tuberculous arthritis mainly
affects the hip and knee. Synovial biopsy shows caseating tuberculous granulomas.
Infective arthritis in syphilis and brucellosis is now rare. Arthritis due to
the spirochaete Borrelia burgdorferi (Lyme disease) and to some fungal
infections such as blastomycosis occurs in outbreaks in the USA and Europe.
The seronegative spondylarthritides are a set of inflammatory arthritides that
involve peripheral joints, as well as the sacroiliac joint and spine; they are
distinguished from rheumatoid disease by the absence of circulating rheumatoid
factor. The cause and pathogenesis of these diseases are not known, but an
autoimmune reaction is suggested by a high incidence of the antigen HLA B27. The
most important conditions are:
• ankylosing spondylitis
• psoriatic arthropathy
• enteropathic arthropathy
• reactive arthritis.
Intervertebral disc disease
Intervertebral disc disease is a common and important cause of back pain and
The intervertebral discs not only permit a limited degree of movement between
adjacent vertebrae, they also act as shock absorbers, and are constantly exposed
to vertical compressive forces. Each disc is composed of cartilaginous
end-plates, with densely collagenous annulus fibrosus surrounding a central
slightly gelatinous nucleus pulposus. The narrow cartilaginous end-plate is most
prominent in the young.
Abnormalities of the disc occur with increasing age; in the elderly the disc
becomes shrunken and has a less gelatinous nucleus pulposus.
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