Gout: A Comprehensive USMLE Guide

Introduction

Gout is a common and painful form of inflammatory arthritis that affects millions of people worldwide. It is caused by the deposition of uric acid crystals in joints, leading to recurrent episodes of severe joint pain and swelling. This guide aims to provide a comprehensive overview of gout, its pathophysiology, clinical presentation, diagnosis, treatment, and management, tailored specifically for the USMLE exam.

Pathophysiology

Gout is primarily caused by hyperuricemia, which refers to elevated levels of uric acid in the blood. This can occur due to either increased production or decreased excretion of uric acid. The excess uric acid forms monosodium urate crystals, which deposit in joints, tendons, and surrounding tissues. The crystals trigger an inflammatory response, leading to the characteristic symptoms of gout.

Clinical Presentation

1. Acute Gouty Arthritis:
   • Sudden onset of intense joint pain, commonly affecting the big toe (podagra).
   • Joint inflammation, redness, and swelling.
   • Limited range of motion due to pain.
   • Symptoms typically peak within 24 hours and resolve spontaneously within a few days to weeks.
2. Chronic Tophaceous Gout:
   • Develops after repeated episodes of acute gouty arthritis.
   • Formation of tophi, which are palpable nodules composed of urate crystals.
   • Tophi can occur in joints, ears, fingertips, and other soft tissues.
   • Chronic joint deformity and damage may occur.

Diagnosis

1. Clinical Presentation:
   • History of recurrent episodes of acute joint pain and swelling.
   • Presence of tophi or joint deformities.
2. Laboratory Tests:
   • Elevated serum uric acid level (>6.8 mg/dL).
   • Synovial fluid analysis shows negatively birefringent needle-shaped crystals under polarized light microscopy.
3. Imaging:
   • X-rays may reveal joint erosions, tophi, and soft tissue swelling.
   • Dual-energy CT scan can identify urate crystal deposits.

Treatment

1. Acute Gouty Arthritis:
   • Nonsteroidal anti-inflammatory drugs (NSAIDs) like indomethacin or naproxen are the first-line treatment.
   • Colchicine is an alternative option, especially for patients with contraindications to NSAIDs.
   • Glucocorticoids (oral, intra-articular, or intramuscular) are used for refractory cases or NSAID intolerance.
2. Chronic Tophaceous Gout:
   • Long-term management focuses on lowering serum uric acid levels to <6 mg/dL.
   • Lifestyle modifications: Weight loss, low-purine diet (avoidance of organ meats, seafood, alcohol), increased fluid intake.
   • Pharmacotherapy:
     • Xanthine oxidase inhibitors (allopurinol, febuxostat) reduce uric acid production.
     • Uricosuric agents (probenecid, lesinurad) enhance uric acid excretion.
     • Febuxostat or pegloticase may be considered for refractory cases.

Complications

1. Uric Acid Nephrolithiasis:
   • Urate crystals can precipitate in the kidneys, leading to kidney stones.
2. Uric Acid Nephropathy:
   • Chronic deposition of urate crystals can cause interstitial nephritis and renal damage.
3. Joint Destruction:
   • Chronic inflammation of joints can result in joint destruction and deformities.

Conclusion

Gout is a common rheumatologic condition characterized by recurrent episodes of acute joint pain and swelling. Understanding the pathophysiology, clinical presentation, diagnosis, treatment, and management of gout is crucial for medical students preparing for the USMLE exam. By following this comprehensive guide, students can enhance their knowledge and confidently tackle questions related to gout on the exam.