Risk factors for psoriatic arthritis development in psoriasis patients: myths, pitfalls, and pearls.

Psoriatic arthritis (PsA) predominantly emerges in individuals previously diagnosed with psoriasis (PsO), offering a unique opportunity to study the transition from PsO to PsA. This progression provides a window to identify characteristics of PsO patients who may develop PsA, facilitating early intervention and potentially informing prevention and treatment strategies. This review evaluates a wide array of research focusing on various risk factors for PsA development. These factors span demographic characteristics, concomitant diseases and habits, characteristics of skin and nail psoriatic disease, and symptoms and imaging abnormalities associated with PsA. By summarising the existing literature, this review critically examines each risk factor, highlighting the strengths and limitations inherent in the studies. Each section of the review not only summarises the current state of knowledge but also includes an expert opinion, culminating in a final concluding remark. This integration allows physicians to utilise the confluence of established literature and ongoing clinical experience, facilitating a rationalised decision-making process that is deeply informed by both empirical evidence and practical insights.

The Challenge of IBD-Related Arthritis Screening Questionnaires in Early and Predominantly Entheseal Phenotypes.

INTRODUCTION: Inflammatory bowel disease (IBD)-related arthritis is recognized as the most prevalent extraintestinal manifestation (EIM) of IBD. The objective of this study was to determine the prevalence and characteristics of undiagnosed IBD-related arthritis and to compare two screening questionnaires, DETection of Arthritis in Inflammatory boweL diseases (DETAIL) and IBd Identification of Spondyloarthritis Questionnaire (IBIS-q), for early disease detection. METHODS: Between April and October 2023, both the DETAIL and IBIS-q questionnaires were administered to consecutive IBD outpatients visiting the University Hospital of Udine, Italy. During routine gastroenterology evaluations, patients aged > 18 years with Crohn's disease (CD) or ulcerative colitis (UC) were requested to complete both questionnaires. Subsequently, all patients who completed the questionnaires underwent a blinded rheumatological evaluation within 2 weeks. Patients with a previous diagnosis of IBD-related SpA were then excluded. RESULTS: Overall, 203 patients were enrolled, of whom 26 were excluded because of a prior diagnosis of inflammatory arthritis. Among the remaining 177 patients, 10/177 (5.6%) received a new diagnosis of IBD-related arthritis. The median duration of symptoms before diagnosis was 4 (IQR 1.8-10.5) months. Imaging-confirmed enthesitis was the predominant pattern in 8 out 10 cases (80%, with 8 out 8 lacking concomitant peripheral arthritis), axial involvement in 1 out 10 cases (10%), and peripheral arthritis in 1 out 10 cases (10%). The DETAIL questionnaire exhibited higher specificity, but lower sensitivity compared to the IBIS-q, with a sensitivity of 40.0% (12.2-73.8) and specificity of 84.4% (78.0-89.6) versus a sensitivity of 70.0% (34.8-93.3) and specificity of 74.3% (66.9-80.7). Both questionnaires performed less effectively than in other studies. CONCLUSION: This study highlights a significant proportion of undiagnosed IBD-related arthritis (5.6%). Enthesitis emerged as the predominant pattern of newly diagnosed arthritis in our cohort, likely due to the recent onset of symptoms. Our study underscores the importance of entheseal involvement in early IBD-related arthritis and the importance of incorporating entheseal involvement into screening questionnaires.

How much different is the semi-quantification of synovitis according to the ultrasound system and the blood flow detection technology?

AIM: To compare synovial blood flow scoring between different technologies and ultrasound (US) systems in active and inactive rheumatoid arthritis (RA). MATERIAL AND METHODS: Fifty-nine RA patients underwent B-mode, power Doppler (PD), colour Doppler (CD), B-Flow and High-Resolution (High-Res) PDI assessments of 6 joints with two US systems at two European centres. Each joint was semi-quantitatively scored for all ultrasound parameters. PD, CD and High-Res PDI synovial signal was also quantitatively scored. RESULTS: Correlations between the total score of SH with system 1 and 2 were very high (≥ 0.90, p<0.0001). Baseline correlations between systems for PD and CD total scores were moderate to very high (0.44-0.96, p<0.05). At baseline, there were no significant differences between ultrasound systems for PD or CD semiquantitative-based total scores in active or inactive patients (p>0,05). B-Flow and High-Res total scores were significantly lower than PD or CD total scores (p<0.05). CONCLUSION: A high-end and an entry-level US system were interchangeable for scoring SH and showed similar sensitivity and responsiveness in scoring synovial blood flow by PD and CD but not interchangeability. B-Flow and High-Res PDI were responsive, but they showed different sensitivity to detect synovial blood flow compared to conventional Doppler.

From Psoriasis to Psoriatic Arthritis: Decoding the Impact of Treatment Modalities on the Prevention of Psoriatic Arthritis.

INTRODUCTION: Biologic therapies are licensed for both psoriasis (PsO) and psoriatic arthritis (PsA) with some electronic medical record data suggest that IL (Interleukin)-23 blockers might be more protective in PsA prevention than TNF blockers; however, the findings have been inconsistent. Higher Psoriasis Area and Severity Index (PASI) scores have also been linked to an increased PsA risk. To clarify these unresolved issues we investigated biologic agents, methotrexate, phototherapy, and topical therapy for PsA prevention in patients with psoriasis. METHODS: This retrospective cohort study analyzed data from 58,671 patients with psoriasis from the Israeli Meuhedet Health Services Organization database was evaluated for incident PsA. Patients were categorized on the basis of treatment: group 1, topical therapy; group 2, phototherapy; group 3, conventional disease-modifying antirheumatic drugs (cDMARDs; methotrexate); group 4, biologic DMARDs which was also stratified according to biologic class. RESULTS: The PsA incidence rate was lower in the biologic agents' group versus the methotrexate group (HR 0.46 [95% CI 0.35-0.62]). The incidence rates per 100 person-years varied across biologic treatment groups, with the anti­IL­12/23 or anti­IL­23p19 group at 4.57, the anti-IL-17 group at 4.35, and the TNF inhibitor group at 2.55. No differences were found between various biological agents in terms of preventing PsA. The phototherapy group exhibited a higher PsA development rate than the topical therapy group (HR 1.85 [95% CI 1.65-2.07]). CONCLUSION: Biological agents are more effective than methotrexate in reducing incident PsA in patients with psoriasis. This lower rate of PsA on topical therapy compared to phototherapy supports the importance of psoriasis severity as a risk factor.

Risk of developing psoriatic arthritis in psoriasis cohorts with arthralgia: exploring the subclinical psoriatic arthritis stage.

OBJECTIVE: Subjects with subclinical psoriatic arthritis (PsA), defined as the presence of arthralgia in psoriasis (PsO), are at higher risk of PsA but scant real-world data exist. Our aims were to (1) estimate the probability of PsA development in subclinical PsA, (2) characterise subclinical PsA symptoms and (3) determine the clinical patterns at PsA diagnosis. METHODS: Patients with PsO, mainly subclinical PsA, were evaluated longitudinally in two European cohorts. The key outcome was new-onset PsA. Musculoskeletal symptoms including inflammatory and non-inflammatory symptoms before PsA diagnosis were collected. Occurrence of PsA was analysed with survival analysis and cumulative incidence functions (CIFs). RESULTS: 384 patients with PsO were included with a mean follow-up of 33.0 (±20.9) months. 311 of 384 (80.9%) had subclinical PsA with a PsA incidence rate of 7.7 per 100 patient-years. Subclinical PsA displayed a higher risk of PsA development compared with PsO (HR=11.7 (95% CI 1.57 to 86.7), p=0.016). The probability of new-onset PsA estimated by the CIF was 9.4% (95% CI 4.7% to 10.6%) at month 12 and 22.7% (95% CI 17.2% to 28.6%) at month 36. 58.9% of cases reported inflammatory symptoms in the months immediately prior to PsA diagnosis but prior non-inflammatory symptoms were evident in 83.9% prior to PsA diagnosis. Peripheral joint swelling was the predominant PsA presentation pattern (82.1%). CONCLUSIONS: The probability of PsA development among subclinical PsA was relatively high, emphasising the importance of emergent musculoskeletal symptoms when aiming for PsA prevention. Joint swelling was the dominant feature in new-onset PsA, likely reflecting clinical confidence in recognising joint swelling.

EULAR recommendations for the management of psoriatic arthritis with pharmacological therapies: 2023 update.

OBJECTIVE: New modes of action and more data on the efficacy and safety of existing drugs in psoriatic arthritis (PsA) required an update of the EULAR 2019 recommendations for the pharmacological treatment of PsA. METHODS: Following EULAR standardised operating procedures, the process included a systematic literature review and a consensus meeting of 36 international experts in April 2023. Levels of evidence and grades of recommendations were determined. RESULTS: The updated recommendations comprise 7 overarching principles and 11 recommendations, and provide a treatment strategy for pharmacological therapies. Non-steroidal anti-inflammatory drugs should be used in monotherapy only for mild PsA and in the short term; oral glucocorticoids are not recommended. In patients with peripheral arthritis, rapid initiation of conventional synthetic disease-modifying antirheumatic drugs is recommended and methotrexate preferred. If the treatment target is not achieved with this strategy, a biological disease-modifying antirheumatic drug (bDMARD) should be initiated, without preference among modes of action. Relevant skin psoriasis should orient towards bDMARDs targeting interleukin (IL)-23p40, IL-23p19, IL-17A and IL-17A/F inhibitors. In case of predominant axial or entheseal disease, an algorithm is also proposed. Use of Janus kinase inhibitors is proposed primarily after bDMARD failure, taking relevant risk factors into account, or in case bDMARDs are not an appropriate choice. Inflammatory bowel disease and uveitis, if present, should influence drug choices, with monoclonal tumour necrosis factor inhibitors proposed. Drug switches and tapering in sustained remission are also addressed. CONCLUSION: These updated recommendations integrate all currently available drugs in a practical and progressive approach, which will be helpful in the pharmacological management of PsA.

Validation and incorporation of digital entheses into a preliminary GLobal OMERACT Ultrasound DActylitis Score (GLOUDAS) in psoriatic arthritis.

OBJECTIVES: The main objective was to generate a GLobal OMERACT Ultrasound DActylitis Score (GLOUDAS) in psoriatic arthritis and to test its reliability. To this end, we assessed the validity, feasibility and applicability of ultrasound assessment of finger entheses to incorporate them into the scoring system. METHODS: The study consisted of a stepwise process. First, in cadaveric specimens, we identified enthesis sites of the fingers by ultrasound and gross anatomy, and then verified presence of entheseal tissue in histological samples. We then selected the entheses to be incorporated into a dactylitis scoring system through a Delphi consensus process among international experts. Next, we established and defined the ultrasound components of dactylitis and their scoring systems using Delphi methodology. Finally, we tested the interobserver and intraobserver reliability of the consensus- based scoring systemin patients with psoriatic dactylitis. RESULTS: 32 entheses were identified in cadaveric fingers. The presence of entheseal tissues was confirmed in all cadaveric samples. Of these, following the consensus process, 12 entheses were selected for inclusion in GLOUDAS. Ultrasound components of GLOUDAS agreed on through the Delphi process were synovitis, tenosynovitis, enthesitis, subcutaneous tissue inflammation and periextensor tendon inflammation. The scoring system for each component was also agreed on. Interobserver reliability was fair to good (κ 0.39-0.71) and intraobserver reliability good to excellent (κ 0.80-0.88) for dactylitis components. Interobserver and intraobserver agreement for the total B-mode and Doppler mode scores (sum of the scores of the individual abnormalities) were excellent (interobserver intraclass correlation coefficient (ICC) 0.98 for B-mode and 0.99 for Doppler mode; intraobserver ICC 0.98 for both modes). CONCLUSIONS: We have produced a consensus-driven ultrasound dactylitis scoring system that has shown acceptable interobserver reliability and excellent intraobserver reliability. Through anatomical knowledge, small entheses of the fingers were identified and histologically validated.

Factors associated to long-term retention rate of Janus kinase inhibitors in a multi-failure rheumatoid arthritis population.

OBJECTIVES: We aimed to retrospectively evaluate retention rate and causes of discontinuation of JAKi in rheumatoid arthritis (RA) patients with particular regards to difficult-to-treat subgroups. METHODS: The diffusion of Janus kinase inhibitors (JAKi) for the treatment of RA has rapidly increased in recent years due to their effectiveness, even in difficult-to-treat subgroups of patients. After the publication of the Oral Surveillance study, the labelling of JAKi was modified, advising against their use in elderly patients and those at risk for cardiovascular events and malignancies. Demographic, clinical, serological and therapeutic characteristics of RA patients treated with JAKi were recorded, including smoking habit and comorbidities. RESULTS: Three hundred and thirty consecutive RA patients were enrolled in the study. Among them, 50.3% patients had previously failed at least two biologic DMARDs. Risk factors for the use of JAKi were reported in 75.5% of patients, 41.5% of them were older than 65 years, 37.6% had smoked, while 48.8% had increased cardiovascular or cancer risk. Anticitrullinated peptide antibodies (ACPA) and combination therapy with conventional synthetic DMARDs were associated with a longer drug persistence and ACPA remained independently associated to a higher retention rate of JAKi also in the subgroup of difficult-to-treat patients. CONCLUSIONS: In conclusion, our study supports the clinical effectiveness of JAKi in RA, even in the multi-failure subgroup of patients, where the risk/benefit ratio overcomes the safety risk. The presence of ACPA and the concurrent use of + cs-DMARD may increase the survival on JAKi in the long term.

Nuts and bolts of salivary gland pathology in primary Sjögren's syndrome.

Primary Sjögren's syndrome (pSS) is a chronic, systemic, inflammatory autoimmune disease characterised by lymphocyte proliferation and progressive damage to exocrine glands. Salivary gland histopathology based on salivary gland biopsy is relevant for the diagnosis of pSS and therefore broadly applied in clinical practice. Tissue can be obtained from labial salivary glands (LSG) biopsy or from major salivary glands (MSG) biopsy, namely the parotid; in this latter scenario, the procedure can be either an open surgical biopsy or a US guided core needle biopsy.In this review we will: i) present the histopathological findings that may be encountered by pathologists on biopsies from pSS patients; ii) discuss the advantages and disadvantages of the surgical and/or imaging guided procedures to obtain tissues from LSG or MSG; iii) describe the histopathological features of lymphoma of MSG in pSS patients.

Sonographic Appearance of Lacrimal Glands in Sjögren's Syndrome at High Risk for Lymphoma Development.

Primary Sjögren's syndrome (pSS) is an autoimmune systemic disease characterized by the destruction of exocrine glands, mainly salivary and lacrimal glands. The diagnosis is generally made upon objective tests aimed at assessing salivary and lacrimal glandular function, autoantibody assays, and the results of labial salivary gland biopsies. A major salivary gland biopsy is usually reserved to assess lymphoproliferative complications. Recently, the sonographic evaluation of the major salivary glands has gained a crucial role in assessing the glandular parenchyma and early detecting abnormalities, while the role of ultrasonography in the assessment of lacrimal glands is still secondary. Our case report is about a male patient who presented parotid gland swelling and purpuric lesions, with preserved salivary and lacrimal glandular function. Considering the presence of risk factors associated with lymphoproliferative development and the peculiar characteristics detected by salivary and lacrimal gland ultrasonography, we performed a parotid gland biopsy, confirming Sjögren's syndrome. Our case demonstrates that lacrimal gland ultrasonography could be implemented, along with major salivary gland ultrasonography, as a routine procedure in evaluating patients with suspected or definite diagnoses of pSS.

Secretagogue effect of PDE4 inhibitor apremilast on human salivary gland organoids obtained from primary Sjögren's syndrome patients.

OBJECTIVES: The aim of the study was to culture vital salivary gland organoids obtained through labial or parotid biopsy of primary Sjögren's syndrome (pSS) patients in order to evaluate their morphological and functional features in basal condition and after stimulation with Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) activator forskolin and phosphodiesterase 4 (PDE4) inhibitor apremilast, their in vitro regenerative capacity and the immune-histological resemblance with original tissue. METHODS: Salivary gland tissues from five pSS patients were processed to obtain vital organoids; swelling assay and cell proliferation tests were performed after forskolin and apremilast application. Immunochemistry evaluation on original salivary gland tissue and corresponding organoids was performed, and secretomics analysis was conducted to assess their functional status. REULTS: After application of forskolin and apremilast, we observed organoid swelling after 30 minutes, compatible with a positive functional status and enhancement of saliva production. In 3 cases, apremilast induced organoid proliferation. All cases were positive for cytokeratin 14 (CK14) and most for cytokeratin 5 (CK5). All the cases were positive for amylase; its secretion, and thus functional status of organoids, was confirmed by its high concentration in the culture medium. A focal ductal differentiation was found in some cases, highlighted by epithelial membrane antigen (EMA) positivity. The more differentiated EMA positive areas were negative for the staminal marker CK14, showing a sort of "complementary staining". CONCLUSIONS: Our data highlighted that differentiated cells and vital functional organoids that recapitulate the development of original salivary glands can be obtained from pSS epithelium. For the first time, the direct stimulating effect of PDE4 inhibitor apremilast on pSS human salivary gland organoids is reported, opening new perspectives on targeting oral dryness with drugs that combine secretagogue and immunomodulatory effects.

Upadacitinib effectiveness and factors associated with minimal disease activity achievement in patients with psoriatic arthritis: preliminary data of a real-life multicenter study.

BACKGROUND: Upadacitinib (UPA) is a selective JAK inhibitor recently approved for the treatment of psoriatic arthritis (PsA). In this post-approval study, we aimed to evaluate the effectiveness and safety of UPA over 24 weeks and identify clinical predictors of response, in a multicentric cohort of patients affected by PsA. METHODS: One hundred and twenty-six patients with PsA treated with UPA were enrolled in 10 Italian centres. UPA effectiveness outcomes, such as the proportion of patients with MDA status, DAPSA remission, and low disease activity, ASDAS-CRP inactive and low disease activity, and change from baseline in DAPSA and ASDAS-CRP scores, were evaluated every 12 weeks until week 24. The proportion of DAPSA minor, moderate, and major improvement, and ASDAS clinically important improvement (CII) and major improvement (MI) were considered as well. All treatment-related adverse events were collected during the observation period. Clinical predictors of MDA response at week 24 were evaluated through multivariate analysis. RESULTS: At baseline, 124/126 (98%) and 54/126 (43%) patients showed peripheral and axial involvement, respectively; 110 (87%) patients were intolerant or resistant to biologic DMARDs.  At 24 weeks, MDA status, DAPSA remission, and ASDAS-CRP inactive disease were achieved in 47%, 23%, and 48% of patients, respectively. Minor, moderate, and major DAPSA improvement was observed in 67%, 39%, and 23%, respectively; while 65% and 35% achieved ASDAS-CRP CII and MI, respectively. The mean change from baseline was 15.9 ± 13.5 (p < 0.001) for DAPSA and 1.21 ± 0.97 (p < 0.001) for ASDAS-CRP. Thirteen patients (10%) discontinued UPA due to a lack of efficacy or non-serious adverse events. No serious adverse events were observed. Male gender (OR 2.54, 95% CI 1.03-6.25 p = 0.043), being naïve to biological DMARDs (OR 4.13, 95% CI 1.34-12.71, p = 0.013) and elevated baseline CRP (OR 2.49, 95% CI 1.02-6.12, p = 0.046) were associated with MDA response at week 24. CONCLUSIONS: This is one of the first real-life studies supporting the effectiveness of UPA and its safety profile in PsA patients. Furthermore, the study identifies predictors of MDA response to UPA treatment at 6 months.

Characterisation of prodromal and very early psoriatic arthritis: a systematic literature review informing a EULAR taskforce.

BACKGROUND: Identifying subjects at risk of imminent psoriatic arthritis (PsA) would allow these subjects to participate in therapeutic interventions to delay or prevent PsA development. METHODS: A systematic literature review (SLR) was conducted in 2021 in Medline, Embase, PubMed, Central databases and international congress abstracts (PROSPERO CRD42022255102). All articles reporting the characteristics of patients transitioning from psoriasis (PsO) to PsA and from undifferentiated arthritis (UA) to PsA were included. Clinical and imaging characteristics were collated before PsA onset and at time of PsA diagnosis. RESULTS: Eighteen of 23 576 references evaluated for PsO/PsA transition were analysed; 14 were cohort studies, 2 case-control studies. Two SLRs were used to enrich the project but were not analysed per se. Of 7873 references focusing on UA to PsA, 3 studies were included. Meta-analysis was not possible due to excessive data heterogeneity. Patients with PsO who developed PsA often reported joint pain, joint tenderness and functional limitations. Arthralgia (PsO, n=669; incident PsA, n=99) was associated with subsequent PsA development. On imaging, subclinical enthesopathy (PsO=325; Incident PsA=39) appeared linked to later PsA development. At the time of PsA onset (incident PsA, N=214), peripheral arthritis, mainly oligo-arthritis (ie, the mean number of swollen joints ranged from 1.5 to 3.2), was the most frequent pattern of clinical presentation. CONCLUSIONS: Joint pain, arthralgia and entheseal involvement detected by imaging were frequent in individuals with PsO at risk for imminent PsA. Very early PsA was mainly oligoarticular. This review informed a EULAR taskforce on transition to PsA.

EULAR points to consider for the definition of clinical and imaging features suspicious for progression from psoriasis to psoriatic arthritis.

BACKGROUND: The transition from psoriasis (PsO) to psoriatic arthritis (PsA) and the early diagnosis of PsA is of considerable scientific and clinical interest for the prevention and interception of PsA. OBJECTIVE: To formulate EULAR points to consider (PtC) for the development of data-driven guidance and consensus for clinical trials and clinical practice in the field of prevention or interception of PsA and for clinical management of people with PsO at risk for PsA development. METHODS: A multidisciplinary EULAR task force of 30 members from 13 European countries was established, and the EULAR standardised operating procedures for development for PtC were followed. Two systematic literature reviews were conducted to support the task force in formulating the PtC. Furthermore, the task force proposed nomenclature for the stages before PsA, through a nominal group process to be used in clinical trials. RESULTS: Nomenclature for the stages preceding PsA onset, 5 overarching principles and 10 PtC were formulated. Nomenclature was proposed for three stages towards PsA development, namely people with PsO at higher risk of PsA, subclinical PsA and clinical PsA. The latter stage was defined as PsO and associated synovitis and it could be used as an outcome measure for clinical trials evaluating the transition from PsO to PsA. The overarching principles address the nature of PsA at its onset and underline the importance of collaboration of rheumatologists and dermatologists for strategies for prevention/interception of PsA. The 10 PtC highlight arthralgia and imaging abnormalities as key elements of subclinical PsA that can be used as potential short-term predictors of PsA development and useful items to design clinical trials for PsA interception. Traditional risk factors for PsA development (ie, PsO severity, obesity and nail involvement) may represent more long-term disease predictors and be less robust for short-term trials concerning the transition from PsO to PsA. CONCLUSION: These PtC are helpful to define the clinical and imaging features of people with PsO suspicious to progress to PsA. This information will be helpful for identification of those who could benefit from a therapeutic intervention to attenuate, delay or prevent PsA development.

Evaluation of the Synovial Effects of Biological and Targeted Synthetic DMARDs in Patients with Psoriatic Arthritis: A Systematic Literature Review and Meta-Analysis.

The aims of this systematic literature review (SLR) were to identify the effects of approved biological and targeted synthetic disease modifying antirheumatic drugs (b/tsDMARDs) on synovial membrane of psoriatic arthritis (PsA) patients, and to determine the existence of histological/molecular biomarkers of response to therapy. A search was conducted on MEDLINE, Embase, Scopus, and Cochrane Library (PROSPERO:CRD42022304986) to retrieve data on longitudinal change of biomarkers in paired synovial biopsies and in vitro studies. A meta-analysis was conducted by adopting the standardized mean difference (SMD) as a measure of the effect. Twenty-two studies were included (19 longitudinal, 3 in vitro). In longitudinal studies, TNF inhibitors were the most used drugs, while, for in vitro studies, JAK inhibitors or adalimumab/secukinumab were assessed. The main technique used was immunohistochemistry (longitudinal studies). The meta-analysis showed a significant reduction in both CD3+ lymphocytes (SMD -0.85 [95% CI -1.23; -0.47]) and CD68+ macrophages (sublining, sl) (SMD -0.74 [-1.16; -0.32]) in synovial biopsies from patients treated for 4-12 weeks with bDMARDs. Reduction in CD3+ mostly correlated with clinical response. Despite heterogeneity among the biomarkers evaluated, the reduction in CD3+/CD68+sl cells during the first 3 months of treatment with TNF inhibitors represents the most consistent variation reported in the literature.

Identification of PsA phenotypes with machine learning analytics using data from two phase III clinical trials of guselkumab in a bio-naïve population of patients with PsA.

OBJECTIVES: Psoriatic arthritis (PsA) phenotypes are typically defined by their clinical components, which may not reflect patients' overlapping symptoms. This post hoc analysis aimed to identify hypothesis-free PsA phenotype clusters using machine learning to analyse data from the phase III DISCOVER-1/DISCOVER-2 clinical trials. METHODS: Pooled data from bio-naïve patients with active PsA receiving guselkumab 100 mg every 8/4 weeks were retrospectively analysed. Non-negative matrix factorisation was applied as an unsupervised machine learning technique to identify PsA phenotype clusters; baseline patient characteristics and clinical observations were input features. Minimal disease activity (MDA), disease activity index for psoriatic arthritis (DAPSA) low disease activity (LDA) and DAPSA remission at weeks 24 and 52 were evaluated. RESULTS: Eight clusters (n=661) were identified: cluster 1 (feet dominant), cluster 2 (male, overweight, psoriasis dominant), cluster 3 (hand dominant), cluster 4 (dactylitis dominant), cluster 5 (enthesitis, large joints), cluster 6 (enthesitis, small joints), cluster 7 (axial dominant) and cluster 8 (female, obese, large joints). At week 24, MDA response was highest in cluster 2 and lowest in clusters 3, 5 and 6; at week 52, it was highest in cluster 2 and lowest in cluster 5. At weeks 24 and 52, DAPSA LDA and remission were highest in cluster 2 and lowest in clusters 4 and 6, respectively. All clusters improved with guselkumab treatment over 52 weeks. CONCLUSIONS: Unsupervised machine learning identified eight PsA phenotype clusters with significant differences in demographics, clinical features and treatment responses. In the future, such data could help support individualised treatment decisions.