Editing Gout (section)

===Differential diagnosis===
The most important [[differential diagnosis]] in gout is [[septic arthritis]].<ref name=Lancet2010/><ref name=PM2010/> This should be considered in those with signs of infection or those who do not improve with treatment.<ref name=PM2010/> To help with diagnosis, a synovial fluid [[Gram stain]] and culture may be performed.<ref name=PM2010/> Other conditions that can look similar include [[Calcium pyrophosphate dihydrate crystal deposition disease|CPPD]] (pseudogout), [[rheumatoid arthritis]], [[psoriatic arthritis]], [[palindromic rheumatism]], and [[reactive arthritis]].<ref name="Dalbeth2016"/><ref name=PM2010/> Gouty tophi, in particular when not located in a joint, can be mistaken for [[basal cell carcinoma]]<ref>{{cite journal |vauthors=Jordan DR, Belliveau MJ, Brownstein S, McEachren T, Kyrollos M |title=Medial canthal tophus |journal=Ophthal Plast Reconstr Surg |volume=24 |issue=5 |pages=403–404 |year=2008 |pmid=18806664 |doi=10.1097/IOP.0b013e3181837a31 }}</ref> or other [[neoplasm]]s.<ref>{{cite journal |vauthors=Sano K, Kohakura Y, Kimura K, Ozeki S |title=Atypical Triggering at the Wrist due to Intratendinous Infiltration of Tophaceous Gout |journal=Hand (N Y) |volume=4 |issue=1 |pages=78–80 |date=March 2009 |pmid=18780009 |doi=10.1007/s11552-008-9120-4 |pmc=2654956}}</ref>
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File:Light microscopy of a touch preparation of a gout tophus, showing urate crystals.jpg|Light microscopy of a touch preparation of a gout [[tophus]], showing needle-shaped crystals.
File:Birefringence microscopy of gout, annotated.jpg|Uric acid crystals in polarized light, showing negative [[birefringence]], with yellow color when aligned parallel to the axis of the red compensator, and blue when aligned perpendicularly to it.<ref>{{cite web |url=https://emedicine.medscape.com/article/329958-workup |title=Gout and Pseudogout Workup |first=Bruce M |last=Rothschild |website=Medscape |access-date=23 September 2020 |archive-date=8 October 2020 |archive-url=https://web.archive.org/web/20201008034412/https://emedicine.medscape.com/article/329958-workup |url-status=live }} Updated: Jun 30, 2020</ref>
File:Birefringence microscopy of pseudogout, annotated.jpg|In contrast, [[Calcium pyrophosphate dihydrate crystal deposition disease|CPPD]] (pseudogout) displays rhombus-shaped crystals with positive birefringence.
File:Gichtfuss im Roentgenbild 002.png|Gout on [[X-rays]] of a left foot in the metatarsal-phalangeal joint of the big toe. Note also the soft tissue swelling at the lateral border of the foot.
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