Pseudogout is, perhaps unsurprisingly, often misdiagnosed as gout. It is another form of crystal arthritis.
Unlike gout, which is caused by urate crystals, pseudogout is caused by calcium pyrophosphate crystals. Patients with pseudogout usually also have chondrocalcinosis, deposits of calcium in the cartilage. Shedding of crystals into the joint produces an acute synovitis which resembles gout.
Pseudogout is more common in women and usually affects the knee or wrist.
Diagnosis is by microscopy of fluid from a joint aspiration. Rhomboidal crystals should be seen under the microscope and X-rays of the joint may show signs of chondrocalcinosis.
Joint aspiration reduces the pain but it may be necessary to use some combination of oral NSAIDs, colchicine and an intra-articular injection of a corticosteroid to control the pain. Unfortunately, there is no treatment that can remove the crystals already present around the joint area.
Kumar and Clarke - Clinical Medicine 4th Edition 1998.