Mapping monosodium urate crystal deposition within metatarsophalangeal joints in tophaceous gout: a dual-energy CT study

Abstract Objectives In gout, monosodium urate (MSU) crystal deposition occurs preferentially within certain joints, particularly the 1st metatarsophalangeal (MTP) joint. The aim of this study was to map the distribution of MSU crystals within the MTP joints in people with tophaceous gout. Methods Bilateral foot dual-energy computed tomography (DECT) scans of 119 people with tophaceous gout were analysed. Each quadrant (dorsal, plantar, medial, and lateral) of the metatarsal head and phalangeal base was scored independently by two trained readers for MSU crystal deposition (9696 sites scored). MSU crystal deposition was considered present if crystals were in contact with or directly adjacent (within 1 mm) to bone or cartilage. Data were analysed using general estimating equations. Results MSU crystal deposition was most frequent at the medial quadrant of the 1st metatarsal head (60%) followed by the plantar quadrants of the 1st and 2nd metatarsal heads and medial quadrant of the 1st phalangeal base (all >30%). The phalangeal bases of the 3rd and 4th MTP joints were rarely affected, particularly the lateral quadrants (1%). Across all joints, there was more MSU crystal deposition at the 1st MTP joint compared with other joints, at the metatarsal head compared with the phalangeal base, and at the plantar and medial quadrants compared with other quadrants (p< 0.0001 for all comparisons). Conclusion In people with tophaceous gout, MSU crystal deposition is unevenly distributed. There is marked variation in sites of deposition not only between different MTP joints, but also within these joints.