Bonnie, your Gecko could be showing signs of gout, but im not a vet and and you would have to do a little research.
Type in "crystal urate in reptiles" into any search engine.
Here's one article I found:
http://www.afip.org/CLDavis/GrossCourse01/zoo.htm
Mineral
Metastatic mineralization is common in reptiles, usually due to dietary imbalances, renal disease (especially gout) or follicular stasis.
Target tissues are Great vessels, kidney, lung and gut.
Rattlesnakes, boids, colubrids, viperidae
Monitors, agamids, iguanas, basilisks, geckos, uromastyx, collared lizards, chameleons, chuckwalla
Chelonians: mineralization not as common as other reptiles.
Frogs and toads: cornea and skin (underlying renal disease or dietary problems)
Gout: renal, visceral and articular gout very common.
Xanthomatosis: high dietary cholesterol, hypercholesterolemia
Common in female geckos, less common in other reptiles
Common in anurans “lipid keratopathy”, Cuban and white’s Tree frogs
Gross: white nodules resembling granulomas, lungs, coelomic surfaces, brain
Histo: nodular accumulations of cholesterol crystals (clefts) surrounded by macrophages, multinucleated cells
Urolithiasis in whites tree frogs (common, cause undetermined)