How to distinguish gout from pseudogout

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Gout and pseudogout are two conditions that cause painful, red, swollen joints. Pseudogout occurs due to the deposition of calcium pyrophosphate dehydrate (CPPD) crystals in to joint spaces.  This particular crystal composition differs from regular gout.  High levels of uric acid in individuals with gout results in the deposition of monosodium urate crystals in to joint spaces. Because of this key difference, pseudogout may also be referred to as pyrophosphate arthropathy.

There are other key differences between gout and pseudogout that allow a physician to accurately diagnose, and thus accurately treat, either condition.  The symptoms and diagnosis of pseudogout differs from gout in the following ways:

Which joints are affected:

-Multiple, large joints are affected in pseudogout, such as knees, wrists, hip and shoulder. This is in contrast to gout which tends to occur in small joints, especially the toes.  Gout most commonly presents in the big toe (called Podagra).

Appearance on x-rays:

-Radiographs show calcification in the articular cartilage of joints affected by pseudogout. The calcification of joint cartilage is called chondrocalcinosis. In regular gout, the calcification of cartilage in joints does not occur.

Microscopic appearance of crystals:

-The calcium pyrophosphate dehydrate crystals floating in joint fluid that is aspirated from joints affected by pseudogout are rhomboid in shape. In contrast, gouty crystals composed of monosodium urate are either needle-shaped or spindle-shaped.

– In pseudogout, aspirated joint fluid displays positive birefringence of crystals under polarized light on microscopy.  Gout crystals, on the other hand, have negative birefringence under polarized light.

NSAIDs, such as indomethacin and ibuprofen, are used in both gout and pseudogout to alleviate the pain and inflammation associated with these joint disorders. Colchicine is another medication commonly used in gout. Colchicine works by inhibiting the migration of specific blood cells, called granulocytes, that are responsible for initiating the inflammation in the joints. Occasionally, high doses of colchicine may be used in a patient with pseudogout.

The other medications that are highly effective in gout, such as allopurinol, sulfinpyrazone and probenicid, are completely ineffective in pseudogout. These gout medications inhibit the formation of urate crystals rather than the CPPD crystals that are the main culprit in pseudogout.

It is possible to misdiagnose pseudogout as gout or as other conditions that manifest as an inflammatory arthritis.  However, the key differences between gout and pseudogout described above should assist in the accurate diagnosis and treatment of both pseudogout and gout in any individual.

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