Which condition is associated with rhomboid crystals that are positively birefringent?

The presence of rhomboid crystals that are positively birefringent is a hallmark of pseudogout, which is caused by the accumulation of calcium pyrophosphate dihydrate (CPPD) crystals in the joint. In polarized light microscopy, these CPPD crystals appear as rhomboid-shaped and demonstrate a characteristic positive birefringence, meaning that they show different colors when rotated under polarized light.

Pseudogout typically presents with acute joint inflammation, and it often affects the knees and wrists. This condition can be distinguished from gout, which is caused by monosodium urate crystals and is characterized by needle-shaped crystals that are negatively birefringent. The identification of these crystal shapes and their birefringent properties is crucial for accurately diagnosing the type of crystal-induced arthropathy.

In summary, the association of rhomboid crystals with positive birefringence is specifically indicative of pseudogout, marking it apart from other arthritic conditions that do not exhibit these crystal characteristics.