Gout is an inflammatory joint disease that primarily affects middle-aged men and postmenopausal women. It is characterized by severe pain and erythema in the big toe and other affected joints. Acute gout may be triggered by diuretics, aspirin, minor trauma, or acute illness. The presence of monosodium urate crystals within phagocytes from synovial fluid aspirates is almost always diagnostic. Calcium pyrophosphate deposition disease ("pseudogout") usually affects larger joints and often follows trauma, surgery, or ischemic heart disease. Microscopic examination of crystals under compensated polarized light is used to differentiate gout and pseudogout. Disorders involving basic calcium phosphate are often more difficult to diagnose and treat but are also less likely to be disabling.