Mapping MSU crystal deposition within MTP joints in tophaceous gout: a dual-energy CT study

In gout, MSU crystal deposition occurs preferentially within certain joints, particularly the first MTP joint. The aim of this study was to map the distribution of MSU crystals within the MTP joints in people with tophaceous gout.

Bilateral foot dual-energy CT (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.

MSU crystal deposition was most frequent at the medial quadrant of the first metatarsal head (60%) followed by the plantar quadrants of the first and second metatarsal heads and medial quadrant of the first phalangeal base (all >30%). The phalangeal bases of the third and fourth MTP joints were rarely affected, particularly the lateral quadrants (1%). Across all joints, there was more MSU crystal deposition at the first 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).

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.