Coffin Lid Crystal

A descriptor for 3–6-sided colorless prism-shaped crystals seen in various fluids
Synovial fluid CLCs are associated with acromegaly, hyperparathyroidism, hemochromatosis, hypomagnesemia, hypophosphatasia, myxedema, ochronosis, Wilson’s disease
DiffDx Other arthritic conditions—e.g., gout, osteoarthritis, rheumatoid arthritis, chondrocalcinosis
Urine Ammonium magnesium phosphate—triple phosphate crystals—seen in neutral or alkaline urine, and linked to urinary tract infections of urea-splitting bacteria