Gout is the deposition of positively birefringent monosodium urate monohydrate crystals in poorly vascularized tissues (synovial membranes, articular cartilage, ligaments, bursae) leading to destruction of cartilage. Two classifications of gout: idiopathic (overproduction of uric acid due to phosphoribosyl transferase deficiency or abnormality of renal urate excretion) and secondary gout (from chronic renal failure, glycogen storage diseases, blood dyscrasias, hypertension, or lead poisoning). Secondary gout is rarely the cause for the radiographic apparent disease. Generally affects males (20:1) over the age of 40 and the incidence is 0.3%.
Stages:
1. Asymptomatic hyperuricemia
2. Acute monarticular gout
3. Polyarticular gout
4. Chronic tophaceous gout (multiple large urate deposits)

The location is most commonly unilateral (15%) in the 1st MTP joint (podagra), hands, elbow, wrist, knee, shoulder, hip, sacroiliac joint. The radiologic features are usually not seen until 6-12 years after the initial attack and are present in 50% of inflicted patients. The soft tissues may demonstrate calcific deposits as in gouty tophi (the sodium urate crystals are not radiopaque). There may be bilateral effusions of the olecran bursae and aural calcifications. The joint space is preserved initially. The joint margins are sclerotic and eroded(resembling rheumatoid arthritis), however there is absence of periarticular demineralization (excludes rheumatoid arthritis). There is cartilage destruction (late disease), periarticular swelling (in acute monarticular gout), and chondrocalcinosis resulting in secondary osteoarthritis. The bones may demonstrate "punched-out" lytic lesions with sclerosis of the margins. The hallmark finding is overhanging margins (40%) which is elevated osseous spicules in sites of tophus formation associated with erosion of adjacent bone (intra- and extra-articular). There can be ischemic necrosis from bone infarction due to deposits at vascular basement membranes.

Coexisting disorders include psoriasis, glycogen storage disease Type 1, hypo- and hyperparathyroidism, Down syndrome, Lesch-Nyhan syndrome (choreoathetosis, spasticity, mental retardation, self-mutilation of lips and fingertips). Gout is not associated with rheumatoid arthritis.