How are BCP crystals identified if they are suspected of causing a joint problem?
Identification of BCP crystals is difficult. If characteristic calcifications are observed on plain radiographs, it is often presumed that BCP is the cause of the symptoms. Aspiration of a calcific deposit may yield material that looks like toothpaste. BCP crystals are so small that individual crystals cannot be appreciated on plain microscopy; however, clumps of aggregated BCP crystals may be seen with an appearance described as stacked, “shiny coins” ( Fig. 47.2 ). Special stains, such as alizarin red, can confirm the presence of calcium in the aspirated material but are not specific for BCP. BCP crystals are not birefringent and are therefore not seen on polarized light microscopy. Precise crystal identification requires techniques such as transmission electron microscopy, which is available only in large referral hospitals and is not practical for the clinician.
