Differences in the Optical Response of MSU and CPP Crystals During Magnetic Orientation: Possibility of Diagnosing Gout and Pseudogout

Pseudogout is crystalline arthritis. It has a similar clinical picture to that of gout, and it is difficult to distinguish the two diseases using conventional analysis methods. However, it is important to identify the different crystals responsible for these two cases because the treatment strategies are different. In a previous study, we reported magnetic orientation of monosodium urate (MSU) crystals, which are the causative agent of gout, at the permanent magnet level. In this study, we investigated the effect of an applied magnetic field on calcium pyrophosphate (CPP) crystals, which are the causative agent of pseudogout, and the difference in the magnetic responses of CPP and MSU crystals. We found that the CPP crystals were oriented in a magnetic field on milli-Tesla order because of the anisotropy of the diamagnetic susceptibility. In addition, the CPP crystals exhibited different anisotropic magnetic properties from those of MSU crystals, which led to a characteristic difference between the orientations of the two crystals. That is, we found that the causative agents of gout and pseudogout responded differently to a magnetic field. This report suggests that the discrimination between CPP and MSU by optical measurements is possible by application of magnetic fields appropriately. © 2023 Bioelectromagnetics Society.