235Validation Data for VAS Pain in Chronic Gout
Construct Validity: VAS pain has statistically signifi cant moderate correlation with
tender joints, SF-36 Physical Component Score (PCS) and HAQ-DI scores (correla-
tion coeffi cients, 0.42–0.56); and statistically signifi cant low correlation with swol-
len joints and SF-36 Mental Component Summary (MCS) (correlation coeffi cient,
0.30–0.36) [ 7 ]. Moderate correlations were observed with SF-36 bodily pain
subscale [ 7 ].
Reliability: Inter-rater or intra-rater assessments were not available for VAS pain
in gout [ 7 ]. Intraclass correlation coeffi cient was 0.97 indicating high reliability of
VAS pain for acute pain measurement in non-gout conditions and pain ratings are
reproducible 90 % of the times [ 55 ].
Clinically meaningful change thresholds: The effect size (ES) and standardized
response mean (SRM) for VAS pain in chronic gout were 0.34 and 0.30, respec-
tively [ 7 ]. Minimal clinically important difference (MCID), moderate improvement,
and really important difference (RID) thresholds for VAS pain scores were 22, 30,
and 50 units, respectively, on a 0–100 mm scale [ 7 ].
Responsiveness to Change for VAS pain in chronic gout (Table 9.4 ): Chronic
refractory gout patients were treated with pegloticase biweekly, pegloticase monthly
vs. placebo ( N = 212; mean age, 55 years). At 25 weeks, the proportion of patients
with pain improvement greater than or equal to MCID of ≥10 points on a 100 mm
VAS was 55 % in pegloticase biweekly vs. 27 % in placebo, a statistically signifi -
cantly result ( p = 0.01) [ 9 ]. A non-randomized crossover 8-week study compared
rilonacept to placebo ( N = 10; mean age, 61 years) in patients with chronic active
gouty arthritis. Median VAS pain scores decreased statistically signifi cantly from
baseline to 8 weeks, from 5.0 at baseline to 2.8 in placebo phase to 1.3 in rilonacept
phase ( p < 0.049) [ 53 ].
Validation Data for Numeric Rating Scale Pain
Similar, but less robust data are available for Numeric Rating Scale (NRS) pain
(0–10) as a PROM for gout. NRS pain had low correlation with activity limitations
(correlation coeffi cient: 0.39). The effect size with NRS scale was 1.62 [ 36 ]. In a
randomized trial of 152 patients with acute gout, the mean change in NRS pain from
baseline to posttreatment was 4.3 with indomethacin and 1.8 with rilonacept (mean
difference, 2.5), i.e., 25 % less improvement in pain with rilonacept [ 56 ].
In summary, VAS pain is a valid PROM in acute and chronic gout. NRS pain has
similar properties, and more validation data are needed. These PROMs can differ-
entiate between therapies as was evident in various treatment comparisons that
showed statistically signifi cant differences in PROMs in acute gout. A few exam-
ples include the following: (1) oral prednisolone was as effective as nonsteroidal
9 PROMs for Gouty Arthritis