Arthritis & Rheumatism, Volume 63,
November 2011 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Chicago, Illinois November 4-9, 2011.


Assessment of Tophus Size; A Comparison Between Physical Measurement Methods and Dual Energy Computed Tomography Scanning.

Dalbeth,  Nicola, Aati,  Opetaia, Gao,  Angela, House,  Meaghan, Liu,  Qiliang, Horne,  Anne, Doyle,  Anthony

Background/Purpose:

A number of methods have been used to assess tophus size in clinical studies of chronic gout, from simple physical measurement techniques to complex advanced imaging methods. Dual energy computed tomography (DECT) has recently been described as a sensitive method to detect urate deposits in patients with gout. The aim of this study was to compare the reliability and validity of various physical methods with DECT assessment of tophus size.

Methods:

Twenty-five patients with a history of gout according to ACR classification criteria and at least one subcutaneous tophus were recruited. For each patient, up to three index tophi were selected for analysis. Sites in the feet were preferentially selected. Tophus location was recorded in detail using a diagram and written description (n=64 tophi, 55 in the feet). Each tophus was assessed by two independent observers using Vernier calipers (longest diameter) and tape measure (area). The total number of subcutaneous tophi was also counted. All patients proceeded to DECT scanning of both feet. Index tophus DECT volume was assessed by two independent observers using automated volume assessment software (n=55 tophi). Five patients returned within one week for repeat physical assessment of tophus size. DECT scans from the returning patients were scored twice by both observers. Intra- and inter-observer reproducibility was assessed by intraclass correlation coefficient and limits of agreement analysis (Bland and Altman).

Results:

Table 1 summarises the reproducibility analysis. Overall, DECT was more reproducible than the physical methods with an interobserver ICC of 0.95 [95% CI 0.92–0.97]. Vernier caliper and tape measurements correlated highly with each other (rs=0.84, p<0.0001) but less well with DECT (for index tophi, rs=0.46, p=0.004 for both). Variation was observed in the amount of urate deposits documented by DECT in tophi of similar physical size (Figure).

Table. Summary of reproducibility analysis for various methods of tophus size.

 Measurement, mean (SD)Intraclass correlation coefficient, mean (95% CI)Bias, mean (SD)
Interobserver reproducibility (Assessor 1 vs. Assessor 2)
Vernier caliper longest diameter25.7 (8.8) mm0.78 (0.66–0.86)2.1 (6.2) mm
Tape measure area895 (713) mm20.88 (0.82–0.93)133 (320) mm2
Tophus count10 (8)0.58 (0.25–0.79)1.8 (8.5)
DECT volume0.62 (1.15) cm30.95 (0.92–0.97)-0.07 (0.36) cm3
Intraobserver reproducibility (Assessment 1 vs. Assessment 2)
Vernier calipers longest diameter28.1 (13.4) mm0.75 (0.54–0.87)-0.4 (10.1) mm
Tape measure area1244 (1186) mm20.91 (0.82–0.96)64 (519) mm2
Tophus count14 (12)0.94 (0.77–0.98)-1.5 (4.3)
DECT volume1.66 (2.1) cm31.00 (1.00–1.00)0.02 (0.13) cm3

Figure. Example of two similar sized tophi from a single patient showing large variation in urate volume (green).

Conclusion:

DECT scanning is a highly reproducible method for assessing tophus volume. This imaging modality reveals the composition of tophi which contain variable urate deposits embedded within soft tissue.

To cite this abstract, please use the following information:
Dalbeth, Nicola, Aati, Opetaia, Gao, Angela, House, Meaghan, Liu, Qiliang, Horne, Anne, et al; Assessment of Tophus Size; A Comparison Between Physical Measurement Methods and Dual Energy Computed Tomography Scanning. [abstract]. Arthritis Rheum 2011;63 Suppl 10 :1618
DOI:

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