What is the most likely diagnosis for a patient presenting with sudden onset of painful swelling in the first toe with negative birefringent crystals in synovial fluid analysis?

Prepare for the Rosh Internal Medicine Boost End of Rotation (EOR) Exam with flashcards and multiple-choice questions. Each question offers hints and explanations to help you excel. Get exam-ready now!

The most likely diagnosis in this scenario is gout, which is characterized by the sudden onset of painful, swollen joints, often affecting the first toe, also known as the podagra. This condition is caused by the accumulation of monosodium urate crystals due to hyperuricemia. The presence of negative birefringent crystals in the synovial fluid is a definitive diagnostic criterion for gout. When viewed under polarized light microscopy, these needle-shaped monosodium urate crystals exhibit negative birefringence, which helps to distinguish gout from other forms of arthritis.

In the context of the other potential diagnoses: pseudogout is associated with calcium pyrophosphate dihydrate (CPPD) crystals, which would present with positive birefringence. Rheumatoid arthritis typically manifests symmetrically and affects multiple joints over time, rather than presenting acutely in a single joint with negative birefringent crystals. Septic arthritis usually presents with fever and is associated with polymorphonuclear leukocytosis in the synovial fluid, often requiring different diagnostic and therapeutic approaches. Therefore, the clinical presentation and synovial fluid analysis align most closely with gout as the correct diagnosis.

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