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An assessment tool for dactylitis Philip Helliwell
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Definition of dactylitis Uniform swelling of a digit such that the soft tissues between the joints are diffusely swollen to the extent that the actual joint swelling can no longer be independently recognised. Adapted from: Rothschild BM, Pingitore C, and Eaton M. Dactylitis: implications for clinical practice. Seminars in Arthritis & Rheumatism. 1998;28:41-7
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Dactylitis instrument based on a surrogate of volume Joint circumference measurement has a long history in rheumatology (but poor inter-rater reliability) Use contralateral digit as comparator Easily measured in both finger and toes Provides a definition for borderline cases eg 10% difference in circumference
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Final instrument Based on finger and toe circumference Incorporates a score for tenderness based on Ritchie method –0 = no tenderness on squeezing –1 = tender –2 = tender and wince –3 = tender and withdraw
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What if opposite digits are involved? Normative data for fingers are available from an anthropometric survey of British workers in the 1980s Normative data for toes required – data on 50 people (1,000 digits) collected for this study
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Case 1: 1 dactylitic finger Score 28.4 Injected with steroid 1 week later score 4.6
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Case 2: 4 dactylitic digits Both 2 nd toes involved Total score 96.1
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Dactylitis – can we agree? Previous work Dafna Gladman has shown moderate inter-observer agreement: Kappa statistic 0.57
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Reliability study 7 patients all with psoriatic arthritis 5 health professionals (4 physicians and 1 specialist nurse) No pre-study training given Assessed patients in turn scoring: –Presence or absence of dactylitis and tenderness score –Measured circumference of all 20 digits Repeated above after interval of 60 minutes
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Circumferometer
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Patient 4 in reliability study
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Patient 1 in reliability study
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Reliability – agreement statistics Percentage exact agreement by joint Kappa statistics for – tender and non-tender dactylitis –Between and within observers
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Percentage exact agreement by digit Median agreement 93%
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Inter observer agreement – first examination Inter observer agreement for presence of tender dactylitis. Kappa statistics are based on recorded tender dactylitis for 140 digits. Tender dactylitis Overall kappa 0.54
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Inter observer agreement – first examination Inter observer agreement for presence of non- tender dactylitis. Kappa statistics are based on recorded tender dactylitis for 140 digits. Non-tender dactylitis Overall kappa 0.17
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Kappa agreement statistics intra-rater Any tender dactylitis: 0.82 Any non-tender dactylitis: 0.58
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Dactylitis instrument Median and inter-quartile range Intra-class correlation coefficients
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Raw dactylitis scores by patient
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ICC statistics 1.Inter-rater 0.90, 95% CI 0.74 – 0.98 2.Intra-rater 0.84, 95% CI 0.71 – 0.92
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Revised instrument Variation may exist as a result of: –Differences in measuring circumference –Differences in judging degree of swelling –Differences in assessing response to squeeze
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Difference in digital circumference for tender dactylitis by examiner Median = 11.7%
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Revised instrument Variation may exist as a result of: –Differences in measuring circumference –Differences in judging degree of swelling –Differences in assessing response to squeeze Revised instrument records presence or absence of tenderness and uses 10% cutoff to define dactylitis
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Revised dactylitis instrument scores
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ICC statistics 1.Inter-rater 0.76 (0.48 – 0.94) 2.Intra-rater 0.91 (0.83 – 0.95)
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ICC statistics 1.Inter-rater 0.76 (0.48 – 0.94) 2.Intra-rater 0.91 (0.83 – 0.95) 1.Inter-rater 0.97 (0.90 – 0.99) 2.Intra-rater 0.91 (0.83 – 0.95)
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Dactylitis instrument - revised Limits of agreement (mean difference ± 2xsd): All raters: - 5.4 ± 37.4 (-2 ± 17) Individual raters: MEANLOA PSH-1.36.8 RDM-19.370.4 GI-3.335.4 JF1.68.4 IS-4.817.2
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Dactylitis assessment tool Quick and easy to measure Intra- and inter-rater reliability: good by ICC individually variable by LOA Still require data on responsiveness in a clinical trial setting
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