In gout, which type of crystals are characteristically observed?

In gout, the characteristic crystals observed are needle-shaped, negatively birefringent crystals, which are specifically monosodium urate crystals. These crystals result from the deposition of uric acid in the tissues and joints, particularly during episodes of acute gout.

The morphology and properties of these crystals are significant for diagnosis. Under polarized light microscopy, monosodium urate crystals exhibit negative birefringence; they appear as needle-shaped and show a distinctive yellow or blue color depending on the orientation of the compensator used in microscopy. This unique appearance helps differentiate gout from other crystal-induced arthropathies.

In contrast, calcium pyrophosphate crystals are associated with pseudogout, while hexagonal crystals are indicative of cystinuria. Amorphous urate crystals may be present in different conditions but do not exhibit the same defining characteristics as those seen in gout. Recognizing these specific properties is crucial in the diagnosis and understanding of gout pathology.