CMS II Rheumatology E1 Practice Exam

Gout crystals on aspiration appear as which of the following?

Blue positively birefringent rhomboid crystals Yellow positively birefringent plate-like crystals Yellow negatively birefringent, long, needle-like crystals parallel to the polarizer Colorless needle-shaped crystals with no birefringence

Correct Answer:

Yellow negatively birefringent, long, needle-like crystals parallel to the polarizer

Explanation:

Gout crystals are monosodium urate crystals seen under polarized light as needle-shaped and negatively birefringent. Because of negative birefringence, they appear yellow when their long axis is parallel to the polarizer and blue when perpendicular. So the description of long, needle-like crystals that are yellow and negatively birefringent when aligned with the polarizer best fits gout. The other patterns point to different crystals (for example, calcium pyrophosphate crystals are rhomboid and positively birefringent and often blue), or to crystals without birefringence.

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