Rosh Internal Medicine Boost Practice Exam

What is the most likely diagnosis for a patient presenting with sudden onset of pain in the first toe and negatively birefringent crystals on synovial fluid analysis?

1. Gout

2. Pseudogout

3. Rheumatoid arthritis

4. Septic arthritis

The correct answer is: Gout

The diagnosis of gout is supported by the presentation of sudden onset pain in the first toe, known as podagra, which is a classic manifestation of this condition. The negatively birefringent crystals observed in synovial fluid analysis are a hallmark of gout, as they indicate the presence of monosodium urate crystals that form due to elevated uric acid levels in the body. This finding is crucial in differentiating gout from other types of arthritis. In contrast, pseudogout, which involves calcium pyrophosphate dihydrate crystals, would show positively birefringent crystals under polarized light, ruling it out in this case. Rheumatoid arthritis typically results in a gradual onset of symptoms and often affects multiple joints, not just the first toe. Septic arthritis would generally indicate the presence of bacteria in the synovial fluid rather than crystalline structures and is associated with systemic signs of infection such as fever, which are not mentioned in this scenario. The combination of symptoms and laboratory findings strongly points to gout as the most likely diagnosis.