Crystal arthritis - overview

Intra-articular crystal deposition is another cause of acute monoarthritis. The presentation can be very similar to septic arthritis with acute episodes of intense pain, redness and visible swelling. Systemic symptoms such as fever and malaise tend to be absent (although fever may be noted); episodes may be triggered by illness, trauma or surgery. There are two common types of crystal arthritis: gout and calcium pyrophosphate deposition disease (CPPD). Definitive identification of crystals is made using polarized light microscopy of aspirated joint fluid. Uric acid crystals are often intra-cellular and appear needle-shaped and yellow (negatively birefringent) while CPPD crystals appear rhomboid shaped and blue (weakly positively birefringent).
Gout - Sodium monourate crystals seen under polarized light. © PEIR Pathology Library (www.peir.net)
Gout - Sodium monourate crystals seen under polarized light. © PEIR Pathology Library (www.peir.net)

The clinical presentation of crystal arthritis may be identical to septic arthritis with acute episodes of intense pain, redness and visible swelling. Systemic symptoms such as fever and malaise tend to be absent (although fever may be noted); episodes may be triggered by illness, trauma or surgery.

Gout

Gout is most prevalent in adult men, with peak incidence in the fourth decade of life. During a gouty attack, the affected joint becomes warm, swollen, red and painful. Pain escalates over an eight to twelve-hour period. Joints that may be involved in the initial attacks are the first metatarsal, the midfoot, ankle, knee, heel, and occasionally the wrist, elbow and/or fingers. The first metatarsal is affected in 50% of preliminary gout attacks and becomes affected in 90% of patients suffering from gout; this is called "podagra".

James Gillray (1757-1815)'s illustration called "The Gout" illustrates the acutely painful nature of this condition.

Radiographic images taken in the early stages of gout show only soft tissue swelling. As gouty arthritis progresses, attacks become more frequent and increase in duration until, in chronic gout, pain persists at a lower intensity even between attacks and the joint is damaged irreversibly. Patients with chronic gout may also be noted to have tophi (macroscopic aggregates of uric acid crystals and inflammatory cells). After years of disease progression, the bones become visibly eroded. Joint space does not diminish until very late in the disease.

Gout is associated with an underlying metabolic cause, hyperuricemia. Hyperuricemia is defined as serum urate concentration more than two standard deviations above that of the general population when matched for age and gender. Only a few (one in four) individuals with hyperurecemia will develop gout and this state is transient for most individuals as it may be altered by diet and/or medication. Increased frequency and duration of hyperurecemia is associated with increased chance of developing gout. Nevertheless, gout may develop in the absence of measurable hyperuricemia, therefore an elevated serum uric acid is not necessary for a positive diagnosis.

CPPD

CPPD is another crystal-related arthropathy; it is sometimes called chondrocalcinosis. CPPD is associated with osteoarthritis and with aging in general. The knee is commonly affected.
Arthroscopic view of knee affected by chondrocalcinosis.
Arthroscopic view of knee affected by chondrocalcinosis.
While it may present in a very similar fashion to gout, it can also be noted as an asymptomatic, incidental finding on x-ray. Seventy-five percent of CPPD patients have radiographic evidence of calcified cartilage. You can link here to the knee xray of a patient with CPPD. Note the calcification in the joint space. The exact etiology of CPPD is unknown, however it is postulated that aging cartilage is more prone to allow the crystallization of calcium containing salts. There are various, less common, other underlying causes, including:
  • Hypothyroidism
  • Hypomagnesemia
  • Hypophosphatasia (reduced alkaline phosphatase)
  • Hemochromatosis
  • Hyperparathyroidism
  • Wilson's disease