The electronic database search identified 2328 unique records; 546 were included in the full-text review, of which 38 publications were included in the SLR, alongside four articles identified through the supplementary searches (Fig. 1). The 42 included articles comprised 27 unique studies (i.e. some articles referred to the same study) of which 21 were cross-sectional and six were longitudinal. Overall, 23 studies reported relevant outcomes for patients assessed by the MDA metric, while fewer reported outcomes for patients assessed by DAPSA (number of studies [NS] = 14), DAS28 (NS = 3) and CDAI (NS = 2); 13 studies included multiple disease activity metrics. There was substantial heterogeneity in the reporting of outcomes and the grouping of patients (ESM Table S8). ESM Fig. S1 presents an overview of the different ways in which patients were grouped in studies, according to disease activity states.
All 27 studies reported relevant residual disease outcomes, and 20 of the studies included residual disease in their study objectives; one study explicitly used a T2T strategy. Studies were distributed across Europe, Asia and North and South America, including 5138 patients with PsA in total; sample sizes ranged from 20 to 624 patients (NS = 27). Where reported, mean age ranged from 41.4 to 59 years (NS = 21). Mean prior disease duration ranged from 3.8 to 15.3 years (NS = 14). Five studies reported patients’ treatment history prior to enrolment (ESM Table S9). Ten studies reported treatments initiated at enrolment: seven studies included conventional synthetic DMARDs and seven included biologic DMARDs (ESM Table S10). Study characteristics are reported in ESM Tables S11 and S12–S17. The quality assessment identified that potential sources of bias were addressed with varying levels of adequacy across studies, although many studies did not report enough detail to fully assess risk of bias (ESM Table S11). A more detailed summary of the quality assessment is provided in ESM Table S18.
Among patients assessed by PsA-specific metrics, 35–85% of each study population (NS = 5) did not achieve MDA or LDA [7, 31,32,33,34,35], 14–100% (NS = 11) achieved at least MDA or LDA (the most commonly reported group) [7, 31, 33,34,35,36,37,38,39,40,41,42,43,44,45] and 12–43% (NS = 6) achieved VLDA or REM (ESM Table S8) [37, 40, 41, 45,46,47,48,49].
Residual Musculoskeletal Disease
Musculoskeletal outcomes were reported in 18 studies (ESM Tables S8, S19–41). Among groups that did not achieve MDA or DAPSA/cDAPSA LDA, 61–91% patients (NS = 6) had a tender joint count (TJC) > 1 (Fig. 2a) [31, 32, 35, 45, 50, 51], and mean TJC ranged from 1.8 to 10.3 (NS = 2) [50, 51]. Across groups that achieved at least MDA or DAPSA/cDAPSA LDA, 2–85% patients (NS = 10) had TJC > 1 (Fig. 2a) [7, 31, 40, 41, 45, 50,51,52,53,54], and mean TJC ranged from 0.3 to 0.8 (NS = 4) [50, 51, 55, 56]. Residual musculoskeletal disease was least evident among groups that reached VLDA, in which 0% patients had TJC > 1 (NS = 4; 9% patients who reached VLDA had TJC = 1 in van Mens et al. [35]), or DAPSA/cDAPSA REM, in which 0–8% patients had TJC > 1 across the same four studies (Fig. 2a) [40, 41, 44, 45, 54]. Similar patterns of residual disease were reported for swollen joint count (SJC; Fig. 2b). A smaller number of studies reported enthesitis (primarily using the Leeds Enthesitis Index [LEI]), tenosynovitis, oligoarthritis and dactylitis, for which residual disease was also observed (ESM Tables S29–S41).
One study reported musculoskeletal outcomes for DAS28-assessed patients, in which 36% patients who had achieved at least LDA (REM + LDA) had TJC > 1; residual SJC, enthesitis, tenosynovitis and dactylitis were also reported for this patient group [7]. One study reported musculoskeletal outcomes for CDAI-assessed patients, in which median TJC28 was 5 (interquartile range: 3–8) among patients in CDAI REM; substantial residual SJC, enthesitis and dactylitis were also reported [57]. For four studies in which patients were assessed using more than one disease activity metric, there were mostly fewer patients with TJC > 1 and SJC > 1 in groups who achieved at least MDA than in groups who achieved at least DAPSA/cDAPSA LDA (Fig. 2) [7, 40, 41, 45]. van Mens et al. reported that 64% patients in VLDA + MDA achieved TJC = 0, compared with 56% in DAPSA REM + LDA (Fig. 2a) [44].
Residual Skin Disease
Skin outcomes were reported in 14 studies (ESM Tables S8, S42–S46). Among groups that did not achieve MDA, mean Psoriasis Area and Severity Index (PASI) score ranged from 2.8 to 4 (NS = 3) [33, 42, 51] and mean body surface area was 12% (NS = 1) [51]; 43–74% patients (NS = 3) had PASI > 1 (Fig. 3) [32, 34, 35, 45]. In the one study that reported PASI for groups that did not achieve DAPSA LDA, 55% patients had PASI > 1 [45]. Among groups that achieved at least MDA, 19–34% patients had PASI > 1 (NS = 3) [34, 35, 40, 45], while 22–42% (NS = 3) of those who achieved at least DAPSA/cDAPSA LDA had PASI > 1 [40, 44, 45]. Among VLDA groups, 0% patients had PASI > 1 across the three studies concerned, whereas among DAPSA/cDAPSA REM groups, 25–39% patients had PASI > 1 across the same three studies (Fig. 3) [40, 44, 45]. Only one study reported skin outcomes (PASI scores) for patients assessed by DAS28 (ESM Table S44) [58]; no skin outcomes were reported for CDAI-assessed patients.
Residual Patient-Reported Disease
PROs were reported in 26 studies (ESM Tables S8, S47–S70). Among groups that did not achieve MDA or DAPSA/cDAPSA LDA, mean patient pain (PtP) on a 0–100 visual analogue scale (VAS; 1–10 VAS transformed where necessary) ranged from 44 to 63 (NS = 3) [39, 51, 58] and from 47 to 66, respectively (NS = 2) [39, 50]. Among groups that achieved at least MDA or DAPSA/cDAPSA LDA, mean PtP VAS ranged from 9 to 25 (NS = 5) [39, 51, 55, 56, 58] and from 18 to 27 (NS = 3) [39, 50, 55], respectively; it was also common to see PtP VAS > 15 in these groups (Fig. 4a). In three studies that assessed patients using multiple disease activity metrics, prevalence of PtP VAS > 15 among patients who achieved VLDA was 0% in the three studies, whereas for patients who achieved DAPSA REM, prevalence of PtP VAS > 15 was 0% in two studies (one of which also reported PtP VAS > 15 for 9% patients in cDAPSA REM) [46] and 10% in the other (Fig. 4a) [41, 45, 46]. PtP VAS was also reported in two studies that used DAS28 and in one study that assessed patients by CDAI [7, 57, 58]; within these studies, residual PtP VAS was reported across all tiers of disease activity, including DAS28/CDAI REM (Tables ESM S47–S51).
Similar patterns of residual disease were observed in findings from the patient global assessment (PtGA) VAS (Fig. 4b) and Health Assessment Questionnaire Disability Index (HAQ-DI; Fig. 5). Among groups that did not achieve MDA or DAPSA/cDAPSA LDA, 80–91% patients (NS = 6) [31, 32, 35, 45, 50, 51] and 84% patients (NS = 1) [45] had PtGA VAS > 20, respectively; 29–80% patients (NS = 6) [31, 32, 35, 45, 50, 51] and 74% patients (NS = 1) [45] had HAQ-DI > 0.5, respectively. Trends like those observed in musculoskeletal and skin outcomes were also seen for both these PROs, with less residual disease in groups with more stringent disease control, and less residual disease in MDA and VLDA groups compared to DAPSA/cDAPSA LDA and REM groups, respectively (Figs. 4b; 5). For example, among VLDA groups, no patients had HAQ-DI > 0.5 in three studies [40, 41, 45, 46] and 8% patients were above this threshold in a further study [37]; among DAPSA/cDAPSA REM groups, 4–15% patients (NS = 4) [37, 40, 41, 45, 46] had HAQ-DI > 0.5.
Five studies that reported PtGA VAS also reported physician global assessment (PhGA) VAS. In different studies and patient groups, there were differing degrees of alignment between PtGA and PhGA; for example, in van Mens et al., median PtGA and PhGA VAS were 6 and 7, respectively, among patients who achieved at least MDA, while medians were 37 and 23, respectively, in patients who did not achieve MDA [35]. Generally, there was a trend for PtGA to be higher (i.e. worse) than PhGA, as demonstrated in the PsArt-ID study in which median PtGA and PhGA VAS among patients who achieved at least MDA were 20 and 10, respectively, while in patients who did not achieve MDA, median PtGA and PhGA were 50 and 35, respectively [31].
Residual disease in treated patients, including those who had met treatment targets, was also evident across PROs that are not components of the MDA metric, DAPSA or the other included metrics (Table 1). These PROs encompassed patient-reported fatigue, disability and quality of life measures, as detailed in ESM Tables S8 and S65–70. The Psoriatic Arthritis Impact of Disease 12-item questionnaire (PsAID-12; range: 0–10, where 10 represents the worst score) [59] was among the more commonly reported of these PROs. Among groups that did not achieve MDA or DAPSA/cDAPSA LDA, mean PsAID-12 ranged from 3.8 to 7.1 (NS = 5) [33, 36, 39, 42, 60] and from 3.9 to 5.3 (NS = 3) [38, 39, 50], respectively. Mean PsAID-12 ranged from 1.1 to 3.5 (NS = 5) among groups that achieved at least MDA [33, 36, 39, 42, 60], and from 1.7 to 2.7 (NS = 3) [38, 39, 50] for those that achieved at least DAPSA/cDAPSA LDA. Mean PsAID-12 in the one study that reported this outcome for a VLDA group was 1.1 [48, 49]; among DAPSA/cDAPSA REM groups, mean PsAID-12 scores of 1.3 and 1.7 were reported in one study [48]. Yedimenko et al. reported median PsAID-12 for patients meeting targets assessed by the MDA metric, DAPSA, and CDAI; for those in MDA or DAPSA/CDAI LDA, median PsAID-12 was 1.5, 2.4 and 1.7, respectively, and in the VLDA or DAPSA/CDAI REM groups, median PsAID-12 was 0.4, 0.7 and 0.5, respectively [61]. None of the included studies reported PsAID-12 for DAS28-assessed patients.