EVIDENCE FOR A CAUSAL RELATIONSHIP BETWEEN THE STRUCTURE, SIZE, AND LOAD OF CALCIUM PYROPHOSPHATE DIHYDRATE CRYSTALS, AND ATTACKS OF PSEUDOGOUT

Objective-To investigate any relationship between the nature, size, an d numbers of synovial fluid (SF) calcium pyrophosphate dihydrate (CPPD ) crystals, and attacks of pseudogout. Methods-Knee SF was aspirated f rom nine selected patients, first during an attack of pseudogout (acut e sample) and again later when the attack had subsided (interval sampl e). CPPD crystals were extracted, weighed, examined by high resolution transmission electron microscopy (HRTEM), and characterised by size a nd crystal habit (monoclinic or triclinic). Structural analysis was ca rried out by x ray powder diffraction (XRD) and the proportions of mon oclinic to triclinic CPPD were estimated from densitometric measuremen ts of selected key reflections. Results-The mean crystal size, by HRTE M, indicated that the crystals in the acute sample were larger than th ose in the interval sample. The ratio of monoclinic to triclinic CPPD, whether estimated from their morphological appearance by HRTEM, or fr om XRD, was greater in the acute than in the interval sample in all ni ne patients. The total amount of extracted mineral varied, but in ever y patient the concentration of CPPD per mi of fluid, and the total min eral per joint, were greater in the acute sample than in the interval sample. Conclusion-In this highly selected group of patients, the larg e numbers of CPPD crystals associated with attacks of pseudogout inclu ded a greater proportion of monoclinic crystals, and larger crystals, than those present when inflammation had subsided. A special, phlogist ic population of crystals may exist, originating in different joint ti ssues, or cleared in a different manner, than the more common populati ons of smaller crystals with a greater proportion of triclinic CPPD, s een in chronic disease.