What condition is characterized by the presence of rhomboid-shaped, positively birefringent crystals in joint fluids?

The condition characterized by the presence of rhomboid-shaped, positively birefringent crystals in joint fluids is pseudogout, also known as calcium pyrophosphate dihydrate (CPPD) crystal deposition disease. In pseudogout, these CPPD crystals tend to precipitate within the synovial fluid in joints, particularly affecting the knee and wrist. The identification of these crystals under polarized light microscopy is fundamental for diagnosis, as the unique rhomboidal shape and positive birefringence are distinctive characteristics that set them apart from monosodium urate crystals found in gout, which are needle-shaped and exhibit negative birefringence.

Pseudogout often mimics the clinical presentation of gout, including acute arthritis episodes, but the underlying pathophysiology relates to the deposition of calcium pyrophosphate crystals rather than uric acid crystals. This distinction is crucial for effective management and treatment strategies in affected patients.