Background The basis as to why chronic gout related tophi may be completely asymptomatic is not understood. In experimental settings coating of gouty crystals may be associated with the prevention of inflammatory responses (1).
Objectives We used optical coherence tomography (OCT) in patients with gout to test the hypothesis that tophus related pain was due to the disruption of tophus capsule.
Methods Eight consecutive patients with tophaceous gout were recruited. Each patient received detailed clinical assessment by a Rheumatologist including physical examination, history, current therapy, presence, number and site of tophi and whether or not each tophus was symptomatic. Tophi were photographed and scanned using Vivosight OCT scan (Michelson Diagnostics, Kent, UK). OCT of corresponding regions of the opposite side were undertaken for comparison and for subclinical tophi evaluation. One hundred slices OCT scans allowed post-processing 3D reconstructions of the visualized superficial tophus morphology (smooth or irregular) and presence or absence of tophus capsule were assessed. VAS pain scores for individual tophi were subsequently collected and correlated with imaging.
Results Thirty seven tophi from eight patients with tophaceous gout were scanned. Four patients had tophi located at fingers, one at toes, two at both sites. Two patients of the third group had additional sites involved in form of multiple aggregates located at knees, heels, elbows. VAS score ranged from 0 to 9 (median=2). Eleven of the 37 tophi were symptomatic (VAS score range: 4–9), the remaining 26 were mildly or not symptomatic (VAS score 0–3). Most of the tophi (28/37) had a smooth border, 9 had an irregular aspect. Tophi with smooth border seemed to be surrounded by a “pseudo-capsule” (p<0.05). Tophi with irregular aspect were associated with optical density changes possibly consistent with oedema (p<0.05). A relationship between irregular tophi and pain was evident (p=0.0025). On the contrary, presence of smooth tophi with capsules were not associated with significant pain.
Conclusions These findings suggest that non-painful tophi in patients with tophaceous gout have a different morphology and a capsule which provides support for the idea that a capsule prevents pain and inflammation. Capsular disruption is linked to flares and the hypothesis that initial serum urate lowering therapy may lead to capsule disruption should be further investigated.
Schauer C et al. Aggregated neutrophil extracellular traps limit inflammation by degrading cytokines and chemokines. Nat Med. 2014;20:511–7
Disclosure of Interest None declared