A patient presents to a physician because of a markedly inflamed and painful great toe. Physical examination additionally demonstrates small nodules on the patient's external ear. Aspiration of the metatarsal-phalangeal joint of the affected toe demonstrates needle-shaped, negatively birefringent crystals. Of which of the following are the crystals most likely composed?

The patient has gout, which is due to precipitation of monosodium urate crystals in joint spaces (notably the great toe) and soft tissues (causing tophi, which are often found on the external ears). Bile pigments are found in some gallstones. Calcium pyrophosphate crystals are deposited in pseudogout, which classically affects the knee or other large joints.Cystine and struvite can form kidney stones. Ref: Namba R.S., Skinner H.B., Gupta R. (2006). Chapter 7. Adult Reconstructive Surgery. In H.B. Skinner (Ed), CURRENT Diagnosis & Treatment in Ohopedics, 4e.