What characteristic finding on arthrocentesis is indicative of gout?

The finding of negatively birefringent needle-shaped crystals on arthrocentesis is highly indicative of gout. This characteristic result is due to the presence of monosodium urate crystals, which form from uric acid that has accumulated in the joints. Gout typically occurs as a result of hyperuricemia and often presents with acute inflammation of the joints, most commonly affecting the big toe.

During the microscopic examination of synovial fluid, these needle-shaped crystals can be observed. When polarized light is applied, these crystals exhibit a unique property where they appear yellow when parallel to the axis of the compensator and blue when perpendicular, which is defined as negative birefringence.

This finding is pivotal for distinguishing gout from other conditions such as pseudogout, where positively birefringent rhomboid-shaped crystals of calcium pyrophosphate dihydrate are present, leading to different clinical and management implications. Understanding this characteristic is essential for accurate diagnosis and treatment planning in patients presenting with joint pain and swelling.