Early radiologic findings in gout are limited to the soft tissues and involve asymmetric swelling in the affected joints. In the intermediate stage of disease, gout causes subtle changes in the bony structures on plain-film radiographs. In the periphery of affected joints, small punched-out lesions arise; obtaining 2 views is important to appreciate these subtle findings. The hallmark sign of late-phase gout is the appearance of large and numerous interosseous tophi on plain-film radiographs. Joint-space narrowing is also prominent in late-phase gout.
Plain film radiography may be used to evaluate gout; however, radiographic imaging findings generally do not appear until after at least 1 year of uncontrolled disease.
As gout is mainly caused by elevated levels of uric acid in the blood, determination of serum uric acid level is the significant blood test for diagnosis. However, it is possible that person with high uric acid levels may not have gout or person with gout may not have elevated levels of uric acid.
Analysis of synovial fluid is the most reliable test for the diagnosis of gout. Joint fluid is obtained by arthrocentesis (joint aspiration) which is performed under local anesthesia. This fluid is analyzed for the presence of uric acid crystals and infection. Shiny, needle-like urate crystals indicate the presence of gouty arthritis. If these urate crystals are found from bursitis fluid and in the material aspirated from tophi, they indicate gout. If the crystals are not found, the diagnosis cannot be made certainly.
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| Radiograph of the foot in a patient with chronic gout. Podagra, or first metatarsophalangeal joint pain, can easily be understood when this radiograph is evaluated. Sclerosis and joint-space narrowing are seen in the first metatarsophalangeal joint, as well as in the fourth interphalangeal joint. |
