What is the characteristic appearance of gout crystals under polarized light microscopy?

Gout is characterized by the presence of monosodium urate crystals, which can be observed under polarized light microscopy. These crystals typically exhibit a negative birefringence when viewed under polarized light. This means that when they are oriented differently in the field of view, they display two distinct colors—this phenomenon is referred to as "dichroism."

The needles shaped as negatively birefringent are important in the identification of gout. In clinical practice, when examining the synovial fluid of a patient suspected of having gout, the identification of these negatively birefringent needle-shaped crystals can confirm the diagnosis. The appearance of the crystals is a key diagnostic feature that distinguishes gout from other types of arthritis, such as pseudogout, which instead features positively birefringent rhomboid-shaped crystals.

Understanding this aspect of gout is critical for proper diagnosis and management, as the presence of these specific crystals indicates a high level of uric acid in the body, often leading to the inflammatory response characteristic of gout attacks.