Crystal-induced synovitis is primarily an illness of middle-aged and elderly adults. Uric acid (gout) and calcium pyrophosphate (pseudogout) are the two most common crystalline agents, with gout representing the most common form of inflammatory joint disease in men older than age 40.5 Patients typically present with joint pain that acutely evolves over hours, as in acute gout attack, or over a single day, as in pseudogout. An acute gout or pseudogout attack often follows trauma, surgery, a significant illness, or change in medications that results in an abrupt change in uric acid levels. Crystalline involvement of joints has a predilection for the lower extremities. Although the first metatarsophalangeal joint is a classic focus for acute gout, no joint is the exclusive site of involvement for either crystal.
The diagnosis of a crystal-induced synovitis is by joint aspiration and identification of crystals through a polarizing microscope. Uric acid crystals appear needle shaped and blue when the source of light is perpendicular to the crystal. Calcium pyrophosphate is yellow in this alignment, with a rhomboid shape. Crystals should be located within phagocytes from aspirates of synovial fluid or inflamed tissues adjacent to the affected joint.
Serum uric acid levels have limited utility in diagnosis, as up to 30 percent of patients will have normal uric acid levels during an acute attack. 5 The joint aspirate WBC is often high with gout, approaching 100,000/mm3 in some cases.5 However, the presence of crystals, absence of findings on Gram stain/culture and, frequently, the dramatic response to nonsteroidal anti-inflammatory drugs (NSAIDs) will clarify the diagnosis. When the diagnosis of a septic joint cannot be excluded, hospital admission until cultures and/or clinical response clarify the diagnosis is the safest course of action.
When the diagnosis of gout or pseudogout is established, a NSAID, such as indomethacin, is standard first-line therapy. All NSAID dosing should be adjusted for renal function and continue for approximately 1 week. For patients with normal renal function, the initial dose of indomethacin is 50 mg. Therapy is continued three times a day for 3 to 5 days. Substantial pain relief typically occurs within 2 h of NSAID administration. 15 Additional treatment for pseudogout is typically not required.
Colchicine, although uncommonly necessary, may also be employed as an alternative in the treatment of acute gout. Oral colchicine is typically administered at a dose of 0.6 mg/h until intolerable side effects (vomiting or diarrhea) or efficacy ensue. Intravenous administration of colchicine, particularly at toxic levels, can be associated with serious side effects, with risks such as bone marrow suppression, neuropathy, myopathy, and death. Consequently, intravenous colchicine is rarely used.
Patient disposition is determined by consideration of effective analgesia and the inclusion or elimination of septic arthritis as a diagnosis in the patient evaluation. Once the symptoms of an acute crystal-induced synovitis episode have resolved, long-term control may be achieved with reduction or elimination of gout-inducing agents (diuretics, aspirin, or cyclosporine) and treatment with prophylactic drugs, such as allopurinol or probenecid.
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