The patient’s acute presentation, combined with negatively birefringent crystals in the synovial fluid, is characteristic of gout.
Gout is caused by elevated uric acid resulting in monosodium urate crystal deposition, most commonly in the big toe, ankle, or knee. Common causes of acute gout include high fat, protein, and alcohol intake, medications that cause elevated uric acid (loop and thiazide diuretics), and chemotherapy, which causes increased cell turnover. Most cases of acute gout are due to undersecretion of uric acid rather than overproduction of uric acid. Patients typically present with severe pain, erythema, and edema, while synovial fluid may reveal an elevated leukocyte count and negatively birefringent, needle-like crystals.
Eggebeen presents an overview of the diagnosis and treatment of gout. First-line treatment of acute gout includes non-steroidal anti-inflammatory medications or corticosteroids. While colchicine is a second-line option, it should be used judiciously due to its side effect profile. Patients with chronic gout, evidence of joint damage, and multiple episodes per year can consider allopurinol, a xanthine oxidase inhibitor, although it should not be initiated during an acute attack.
Neogi discusses the management of acute gout. She comments that, while synovial fluid analysis is the gold standard of diagnosis, many physicians do not routinely perform it, instead relying on clinical judgment to diagnose gout. The differential diagnosis for a gout-like presentation includes pseudogout, septic arthritis, lyme arthritis, reactive arthritis, and rheumatoid arthritis.
Figure A shows sodium urate crystals, which appear as negatively birefringent, needle-like crystals under polarized light.
Answer 1: Lyme disease typically also presents as a monoarticular arthritis, but this patient does not have a history of Lyme disease, and crystals would not be present in the synovial fluid.
Answer 2: Septic arthritis typically has higher leukocyte counts in the synovial fluid, and organisms can be visualized in the fluid.
Answer 3: Pseudogout is characterized by positively birefringent crystals.
Answer 5: The patient does not have a history of rheumatoid arthritis, and this condition typically does not have an acute onset.
Eggebeen AT.Gout: an update.Am Fam Physician. 2007 Sep 15;76(6):801-8.
PMID:17910294 (Link to Abstract)
Neogi T.Clinical practice. Gout.N Engl J Med. 2011 Feb 3;364(5):443-52. doi: 10.1056/NEJMcp1001124.
PMID:21288096 (Link to Abstract)