Magnetic orientation of monosodium urate crystals in microspaces: Potential for gout diagnosis

The current definitive diagnosis of gout requires aspiration of joints, which is a painful procedure for the patient. This study aimed to verify the fundamental principle of a noninvasive diagnostic method based on the changes in the reflection of near-infrared light due to the orientation of monosodium urate (MSU) crystals by an applied magnetic field in a microscopic space that mimics an actual joint. In experiments using a finger joint phantom and thin-layer cells with thicknesses of 50–800 µm, a clear change in the reflected-light intensity in response to magnetic-field application was observed in both, demonstrating that the crystals with a length of approximately 15 µm orient even in extremely narrow spaces. Furthermore, the lack of dependence of the orientation time on the size of the narrow space indicates that the crystals can orient freely and are not significantly affected by wall surfaces. This strongly suggests that even within a narrow joint cavity, crystals can exhibit the orientation behavior necessary for gout diagnosis without adhering to the bone surfaces. This study provides experimental support for the proposed method as a realistic approach for diagnostic applications through detection of MSU crystals in human joints.