Diagnosing and Treating Systemic Juvenile Idiopathic Arthritis and Adult-Onset Still's Disease as Part of the Still's Disease Continuum.

Aim: We have summarised the existing evidence supporting the concept that systemic juvenile idiopathic arthritis (sJIA) and adult-onset Still's disease (AOSD) are part of the same Still's disease spectrum. Methods: A PubMed/Embase database search was conducted using specific search strings and free text words to screen for relevant articles. The search was limited to studies in humans, published up to June 2023, in English-language. Summary: sJIA and AOSD are rare autoinflammatory disorders that have similar pathophysiological and clinical features. The clinical presentations of sJIA and AOSD are highly variable, with differential diagnoses that include a broad range of malignancies, infectious diseases, and autoimmune disorders, which contribute to delays in diagnosis. Several sets of classification exist to help diagnose patients in clinical practice; the International League of Associations for Rheumatology criteria for sJIA and the Yamaguchi and Fautrel criteria for AOSD are the most-used criteria. The therapeutic strategy for Still's disease aims to relieve signs and symptoms, prevent irreversible joint damage and potentially life-threatening complications, and avoid deleterious side effects of treatment. Recently, targeted therapies such as interleukin (IL)-1 and IL-6 inhibitors have become available for the treatment of sJIA and AOSD. While these biologics were originally largely reserved for patients in whom non-steroidal anti-inflammatory drugs, corticosteroids and conventional synthetic disease-modifying anti-rheumatic drugs had failed, they are increasingly used earlier in the treatment paradigm. Among IL-1 inhibitors, canakinumab is the only biologic approved in the US for the treatment of both sJIA and AOSD.

New insights on multigenic autoinflammatory diseases.

Autoinflammatory diseases are disorders of the innate immune system, which can be either monogenic due to a specific genetic mutation or complex multigenic due to the involvement of multiple genes. The aim of this review is to explore and summarize the recent advances in pathogenesis, diagnosis, and management of genetically complex autoinflammatory diseases, such as Schnitzler's syndrome; adult-onset Still's disease; synovitis, acne, pustulosis, hyperostosis, osteitis syndrome/chronic recurrent multifocal osteomyelitis/chronic non-bacterial osteomyelitis; Adamantiades-Behçet's disease; Yao syndrome; and periodic fever with aphthous stomatitis, pharyngitis, and adenitis syndrome. The PubMed database was screened for relevant articles using free text words and specific search strings. The search was limited to English-language articles, reporting the results of studies in humans, published through March 2021. Evidence from literature suggest that these rare multigenic autoinflammatory diseases can present with different clinical features and the diagnosis of these diseases can be challenging due to a combination of nonspecific manifestations that can be seen in a variety of other conditions. Diagnostic delays and disease complications may occur due to low disease awareness and the lack of pathognomonic markers. The pathogeneses of these diseases are complex and in some cases precise pathogenesis is not clearly understood. Conventional treatments are commonly used for the management of these conditions, but biologics have shown promising results. Biologics targeting proinflammatory cytokines including IL-1, IL-6, TNF-α, IL-17A and IL-18 have been shown to ameliorate signs and symptoms of different multigenic autoinflammatory diseases.

Adult-onset Still's disease in focus: Clinical manifestations, diagnosis, treatment, and unmet needs in the era of targeted therapies.

BACKGROUND: Adult-onset Still's disease (AOSD) is a rare systemic inflammatory disorder of unknown etiology, characterized by a clinical triad of high spiking fever, arthralgia (± arthritis), and evanescent skin rash. Management of AOSD poses several challenges, including difficulty in diagnosis and limited therapeutic options. In this review, we examined whether AOSD and systemic juvenile idiopathic arthritis (SJIA) represent a continuum of the same disease. We also explored the latest available evidence related to prevalence, clinical and laboratory manifestations, complications, diagnostic challenges, novel biomarkers, and treatment options in the era of biologics and identified the unmet needs of patients with AOSD. METHODS: A comprehensive systematic literature search was performed in the Embase and MEDLINE (via PubMed) literature databases. The search was limited to human studies published in English from inception up to March 2020. Additionally, abstracts presented at various conferences were screened and hand searches were performed. Publications were processed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. RESULTS: A total of 123 publications were identified through the literature search, majority of which were case series and retrospective observational studies. AOSD and SJIA are widely considered part of the same disease spectrum owing to similarities in their clinical and biological features. The clinical presentation of AOSD is highly variable, accompanied by a broad spectrum of disease manifestations. Recent evidence suggests that the AOSD disease course can be classified into two distinct categories: "systemic" and "articular." Furthermore, AOSD patients may experience various life-threatening complications, such as macrophage activation syndrome - reported in as high as 23% of AOSD patients and considered to be the most severe complication characterized by a high mortality rate. The ambiguity in presentation and lack of serologic markers make the diagnosis of AOSD difficult, often leading to a delay in diagnosis. Given these limitations, the Yamaguchi and Fautrel criteria are the most widely used diagnostic tools in clinical practice. It has been observed that a clinical diagnosis of AOSD is generally reached by exclusion while investigating a patient with fever of unknown origin. Recent advances have demonstrated a major role of proinflammatory cytokines, such as interleukin (IL)-1, IL-6, IL-18, and IL-37, and other biomarkers in the pathogenesis and management of AOSD. Owing to the rarity of the disease, there are very limited clinical trials evaluating management strategies for AOSD. The current AOSD treatment paradigm includes non-steroidal anti-inflammatory drugs (NSAIDs) and glucocorticoids initially, conventional synthetic disease-modifying anti-rheumatic drugs in steroid-refractory patients, and biologics in those resistant to conventional treatment. Only a few country-specific guidelines for the management of AOSD have been published, and a treat-to-target approach, as previously recommended for SJIA, is still lacking. Canakinumab is the only FDA-approved biologic for the treatment of AOSD. CONCLUSION: Emerging evidence supports that AOSD and SJIA represent a continuum of the same disease entity. Despite advancements in the understanding of AOSD, it continues to pose a substantial burden on patients and the healthcare systems, and substantial unmet needs exist across key domains such as the pathway to diagnosis, use of biomarkers in clinical practice, and standardized treatment strategies. Further research and collaboration is crucial for optimizing the diagnosis and management of AOSD patients.

Racial/Ethnic variations in morbidity and mortality in Adult Onset Still's Disease: An analysis of national dataset.

OBJECTIVES: Adult Onset Still's Disease (AOSD) is a rare autoinflammatory disorder. There is relatively little known about the impact of social determinants of health on its outcomes. Our goal is to describe the racial/ethnic variations, morbidity and mortality of AOSD hospitalized patients in the US. MATERIALS AND METHODS: Adult US hospitalized patients between 2009-13 from a nationwide inpatient sample (NIS) database with AOSD were identified using ICD-9 code 714.2. NIS is the largest all-payer US inpatient database with approximately 8 million hospitalizations yearly. Patients with other autoimmune diseases were excluded. We used descriptive statistics to summarize patient and hospital characteristics. We performed survey-weighted logistic regression models adjusting for confounders to study our primary outcome: in-hospital mortality. RESULTS: Between 2009-13, 5,820 AOSD patients were hospitalized with a mean age of 53.6 (SE-0.61) years. 3817 (65.6%) were female, 56% white and 3% Asian. Macrophage Activating Syndrome (1.7%), Disseminated Intravascular Coagulation (DIC-1.1%) and Thrombotic Thrombocytopenic Purpura (0.4%), respectively, complicated the hospital course. There were 154 inpatient deaths in study period (mortality 2.6%). Mean age of patients who died in hospital was higher (62.4 years ± 3.1) and 13.9% were Asians. Patients of Asian origin had significantly higher odds of in-hospital death compared to whites (aOR = 6.39, 95% CI 1.77-23.1, p = 0.005). Mortality was significantly higher for patients whose hospital course was complicated by DIC (aOR = 29.69, 95% CI 5.5-160.41, p = 0.006). CONCLUSIONS: In this national sample of patients hospitalized for AOSD, we found significant variations in In-hospital mortality.

Efficacy and safety of canakinumab in patients with Still's disease: exposure-response analysis of pooled systemic juvenile idiopathic arthritis data by age groups.

OBJECTIVES: To describe the efficacy, safety, and exposure-response relationship of canakinumab in a subgroup of patients with systemic juvenile idiopathic arthritis (SJIA) aged ≥16 years, representative of adult-onset Still's disease (AOSD) patients, and to compare this subgroup with those of children and young adolescents with SJIA by pooling clinical data collected during the development programme of canakinumab. METHODS: Safety and efficacy data on canakinumab-treated patients were pooled from 4 SJIA studies (NCT00426218, NCT00886769, NCT00889863, and NCT00891046). In the majority of patients, canakinumab was administered at 4 mg/kg every 4 weeks. Efficacy parameters (adapted American College of Rheumatology [aACR] paediatric and juvenile idiopathic arthritis [JIA] ACR responses), quality of life, C-reactive protein levels, safety, and exposure-response relationship were assessed over 12 weeks in 3 age groups (children 2-<12, young adolescents 12-<16 and older adolescents and young adults ≥16 years). RESULTS: Efficacy outcomes were analysed in 216 children, 56 young adolescents and 29 older adolescents and young adults. Efficacy parameters across 3 age groups were largely comparable. At Day 15, at least 50% of patients from each age group exhibited aACR ≥70 and ACR responses. The safety profile of canakinumab was similar across age groups. One death was reported. CONCLUSIONS: Pooled analyses from SJIA studies indicate that older adolescents and young adults SJIA patients show similar efficacy, safety, and exposure-response relationship on a weight-based dosing regimen as observed in children and adolescent SJIA patients. These analyses suggest that canakinumab may be an effective therapy in young adults with Still's disease.

Tumor necrosis factor-associated periodic syndrome in adults.

Tumor necrosis factor-associated periodic syndrome is an autoinflammatory disorder classified under hereditary periodic fever syndromes. Mutations in the tumor necrosis factor receptor contribute to tumor necrosis factor-associated periodic syndrome. Decreased shedding of receptors and increased mitochondrial reactive oxygen species production leading to elevated proinflammatory cytokines are documented. Inflammation in various organs is hallmark of tumor necrosis factor-associated periodic syndrome and manifests as spiking fever, abdominal pain, conjunctivitis and polyserositis in adults. The ongoing challenge is to diagnose the disease early in its course to prevent amyloidosis. The treatment options have evolved from use of nonsteroidal anti-inflammatory drugs and corticosteroids to targeted therapy like tumor necrosis factor receptor inhibitors and interleukin-1 blockers. The aim of this review is to give an overview of the pathogenesis, clinical features and the various treatment modalities available for tumor necrosis factor-associated periodic syndrome and aid physicians in recognizing the signs of the disease earlier.

IgG4-related disease: a complex under-diagnosed clinical entity.

IgG4-related disease (IgG4-RD) encompasses a spectrum of complex fibro-inflammatory disorders which are often under diagnosed due to unfamiliarity by clinicians. A challenging multitude of clinical manifestations makes the diagnosis cumbersome. The primary clinical feature in IgG4-RD entails a tumor-like presentation coupled with tissue-destructive lesions. Histopathological findings include lymphoplasmacytic infiltrate, storiform fibrosis, and obliterative phlebitis. These findings, in combination with elevated serum immunoglobulin G4 levels, are diagnostic in the setting of single- or multi-organ involvement. A closer understanding of the role of T cells and B cells in the increased production of IgG4 has led to a notion that IgG4 can act as a pathogen, anti-inflammatory agent, or rheumatoid factor. Glucocorticoids are the primary treatment modality; however, relapse is common with prolonged therapy. Alternatively, immunomodulatory agents are being increasingly used as therapy. The aim of this article is to raise awareness of IgG4-RD and review the diagnostic algorithm, as IgG4-RD often mimics a wide array of clinical conditions. In addition, we summarize the pathogenesis and current treatment guidelines of IgG4-RD for clinicians. Awareness and accurate diagnosis are crucial in preventing progression to chronic diseases, thereby diminishing disease-related morbidity and mortality.

Recommendations for optimizing methotrexate treatment for patients with rheumatoid arthritis.

Methotrexate (MTX) remains the cornerstone therapy for patients with rheumatoid arthritis (RA), with well-established safety and efficacy profiles and support in international guidelines. Clinical and radiologic results indicate benefits of MTX monotherapy and combination with other agents, yet patients may not receive optimal dosing, duration, or route of administration to maximize their response to this drug. This review highlights best practices for MTX use in RA patients. First, to improve the response to oral MTX, a high initial dose should be administered followed by rapid titration. Importantly, this approach does not appear to compromise safety or tolerability for patients. Treatment with oral MTX, with appropriate dose titration, then should be continued for at least 6 months (as long as the patient experiences some response to treatment within 3 months) to achieve an accurate assessment of treatment efficacy. If oral MTX treatment fails due to intolerability or inadequate response, the patient may be "rescued" by switching to subcutaneous delivery of MTX. Consideration should also be given to starting with subcutaneous MTX given its favorable bioavailability and pharmacodynamic profile over oral delivery. Either initiation of subcutaneous MTX therapy or switching from oral to subcutaneous administration improves persistence with treatment. Upon transition from oral to subcutaneous delivery, MTX dosage should be maintained, rather than increased, and titration should be performed as needed. Similarly, if another RA treatment is necessary to control the disease, the MTX dosage and route of administration should be maintained, with titration as needed.

Oxygen-Dependent Patient with Antisynthetase Syndrome Associated Interstitial Lung Disease Responds Promptly to Rituximab with Rapid Pulmonary Function Improvement.

Antisynthetase syndrome (anti-SS) is a rare systemic autoimmune disorder characterized by myositis, Raynaud's phenomenon, fever, interstitial lung disease (ILD), polyarthralgia, and presence of antibodies against tRNA synthetase, especially anti-Jo-1. Rarely, anti-SS can present as isolated ILD, with clinical features very similar to atypical pneumonia, making diagnosis extremely challenging. We report a patient originally diagnosed with atypical pneumonia, requiring oxygen supplementation, who failed treatment with antibiotics. Radiological findings were suspicious for ILD and a comprehensive rheumatological work-up revealed the diagnosis of anti-SS associated ILD. Prompt treatment was initiated with steroids and rituximab. Follow up pulmonary function tests showed an improvement in her diffusing capacity of the lung for carbon monoxide and forced vital capacity allowing her to resume her daily life without supplemental oxygen.

Autoimmune/Inflammatory Arthritis Associated Lymphomas: Who Is at Risk?

Specific autoimmune and inflammatory rheumatic diseases have been associated with an increased risk of malignant lymphomas. Conditions such as rheumatoid arthritis (RA), primary Sjögren's syndrome (pSS), systemic lupus erythematosus (SLE), dermatomyositis, and celiac disease have been consistently linked to malignant lymphomas. Isolated cases of lymphomas associated with spondyloarthropathies and autoinflammatory diseases have also been reported. Direct association between autoimmunity and lymphomagenesis has been reinforced by large epidemiological studies. It is still uncertain whether disease specific determinants or phenotypic or treatment related characteristics increase likelihood of lymphomagenesis in these patients. For example, recent literature has indicated a positive correlation between severity of inflammation and risk of lymphomas among RA and Sjögren's syndrome patients. It is also debated whether specific lymphoma variants are more commonly seen in accordance with certain chronic autoimmune arthritis. Previous studies have revealed a higher incidence of diffuse large B-cell lymphomas in RA and SLE patients, whereas pSS has been linked with increased risk of mucosa-associated lymphoid tissue lymphoma. This review summarizes recent literature evaluating risk of lymphomas in arthritis patients and disease specific risk determinants. We also elaborate on the association of autoimmune arthritis with specific lymphoma variants along with genetic, environmental, and therapeutic risk factors.

Inadequate response or intolerability to oral methotrexate: Is it optimal to switch to subcutaneous methotrexate prior to considering therapy with biologics?

Methotrexate (MTX) is considered an anchor drug in the treatment of rheumatoid arthritis. It is also the first-line therapy in a multitude of rheumatologic conditions. Low-dose oral MTX is the preliminary modality of treatment for rheumatoid arthritis due to its affordability, favorable outcomes, and limited risks. However, patients refractory to low-dose MTX therapy may require larger doses of oral MTX. Several studies in the past have demonstrated variability in bioavailability of oral MTX at high doses. This warrants a subsequent switch to parenteral MTX. Widely used among the parenteral preparations of MTX is subcutaneous (SC) MTX. SC MTX provides dependable efficacy, predictable bioavailability, sustained clinical outcomes, and minimal GI adverse effects. It is useful either singularly or in combination therapy regimens. Although SC MTX and intramuscular MTX have similar pharmacokinetics, SC MTX may be preferred by most patients. Development of prefilled syringes and auto-injectors have enabled self-administration of the medication providing the patients with a sense of independence and improved general well-being. Hence, SC MTX can prove to be more efficacious in patients refractory to oral MTX therapy or in patients experiencing severe gastrointestinal adverse effects.

Impact of IL-1 inhibition on fatigue associated with autoinflammatory syndromes.

Cryopyrin-associated periodic syndromes (CAPS) is a rare group of autoinflammatory disorders that includes familial cold autoinflammatory syndrome or FCAS, Muckle-wells syndrome or MWS, and neonatal-onset multisystem inflammatory disease or NOMID. CAPS is caused by a mutation in the NOD-like receptor family, pyrin domain containing 3 (NLRP3) gene. This ultimately leads to increased production of interleukin (IL)-1ß. IL-1ß is a biologically active member of the IL-1 family. It is not only a pro-inflammatory cytokine responsible for features such as fever, rash, and arthritis, but is also a major mediator in the central pathways of fatigue. Fatigue is a major component of CAPS and is associated with severely compromised quality of life. In clinical studies, fatigue was measured using functional assessment of chronic illness therapy-fatigue or FACIT-F and short form-36 or SF-36, physical component score instruments. These questionnaires can also be used to monitor improvement of fatigue following initiation of therapy. IL-1 inhibitors block the IL-1 signaling cascade, thereby preventing systemic inflammation in CAPS. The decrease in systemic inflammation is accompanied by improvement in fatigue.

Screening Optimization of Latent Tuberculosis Infection in Rheumatoid Arthritis Patients.

Objective. Rheumatoid arthritis (RA) patients are at increased risk of latent tuberculosis infection (LTBI) but there are no clear guidelines for LTBI screening with Tuberculin Skin Test (TST) or Quantiferon TB Gold testing (QFT-G). Methods. A retrospective study was conducted in a high risk, largely foreign-born, inner city, RA population. After screening 280 RA patients, 134 patients who had both TST and QFT-G testing performed during their initial evaluation were included. Results. Out of 132 RA patients included in our analysis, 50 (37.8%) patients were diagnosed with LTBI with either positive TST 42 (31.8%) or QFT-G 23 (17.4%). 15 (11.4%) were positive and 82 (62.1%) were negative for both tests. The agreement between TST and QFT-G was 73.5% (Kappa 0.305, CI = 95% 0.147-0.463, p = 0.081). Conclusions. There was low-moderate agreement (κ = 0.305) between TST and QFT-G. In the absence of clearly defined gold standard and limitations associated with both tests, we propose early screening with both tests for patients who need prompt treatment with BRMs. Patients who are not immediate candidates for BRM treatment may be safely and cost effectively screened with a two-step process: initial screening with TST and if negative, IGRA testing. Patients positive for either test should be promptly treated.

Use of B lymphocyte stimulator inhibitor belimumab may be associated with a decrease in the serum concentration of epidermal growth factor in patients with primary Sjögren's syndrome.

B cell activating factor (BAFF), also called the B lymphocyte stimulator, has been known to show increased expression in primary Sjögren's syndrome (pSS) which could explain increased B cell activation characteristic of this disease. Belimumab, a fully human IgG1λ recombinant monoclonal antibody directed against B lymphocyte stimulator (Blys), has been reported to be efficacious in systemic lupus erythematosus (SLE) through its B cell-mediated action. Randomized controlled trials of belimumab in a selected target population of pSS patients are further warranted.

Adult-onset Still's disease-pathogenesis, clinical manifestations, and new treatment options.

Adult-onset Still's disease (AOSD), a systemic inflammatory disorder, is often considered a part of the spectrum of the better-known systemic-onset juvenile idiopathic arthritis, with later age onset. The diagnosis is primarily clinical and necessitates the exclusion of a wide range of mimicking disorders. AOSD is a heterogeneous entity, usually presenting with high fever, arthralgia, skin rash, lymphadenopathy, and hepatosplenomegaly accompanied by systemic manifestations. The diagnosis is clinical and empirical, where patients are required to meet inclusion and exclusion criteria with negative immunoserological results. There are no clear-cut diagnostic radiological or laboratory signs. Complications of AOSD include transient pulmonary hypertension, macrophage activation syndrome, diffuse alveolar hemorrhage, thrombotic thrombocytopenic purpura and amyloidosis. Common laboratory abnormalities include neutrophilic leukocytosis, abnormal liver function tests, and elevated acute-phase reactants (ESR, CRP, ferritin). Treatment consists of anti-inflammatory medications. Non-steroidal anti-inflammatory drugs have limited efficacy, and corticosteroid therapy and disease-modifying anti-rheumatic drugs are usually required. Recent advances have revealed a pivotal role of proinflammatory cytokines such as tumor necrosis factor-α (TNF-α), interleukin (IL)-1, IL-6, IL-8, and IL-18 in disease pathogenesis, giving rise to the development of novel targeted therapies aiming at optimal disease control. The review aims to summarize recent advances in pathophysiology and potential therapeutic strategies in AOSD.

A novel therapeutic approach in pulmonary arterial hypertension as a complication of adult-onset Still's disease: targeting IL-6.

Adult-onset Still's Disease (AOSD), often though as the adult variant of systemic juvenile idiopathic arthritis (JIA), has an incidence of 1-3 cases per 1 million. Cardinal manifestations include fever, arthritis, skin rash, sore throat, hepatosplenomegaly and lymphadenopathy. Prolongation in diagnosing this disease results from its similarity to infectious, malignant and rheumatic diseases and lack of biomarkers. Pulmonary arterial hypertension (PAH) is a rare pulmonary complication of AOSD, and we are aware of only six cases reported in literature to date. Here we present a patient with AOSD who has developed pulmonary hypertension as a complication. We report a case of AOSD complicated by PAH treated successfully with tocilizumab, a humanized monoclonal antibody to human interleukin (IL)-6 receptor. A Pubmed and Medline search for evidence of pulmonary hypertension in AOSD and use of IL-6 inhibition in management was performed. Data for this study was collected from the patient's chart records. No infectious or neoplastic cause of her disease was identified and after extensive diagnostic workup, the patient was diagnosed with AOSD fulfilling Yamaguchi criteria. After initiation of IL-6 therapy the patient was followed over time to monitor the hemodynamic changes in pulmonary vasculature. Following treatment with Tocilizumab, the patient showed dramatic improvement in her clinical symptoms and remains in remission, through combination of tocilizumab (8 mg/kg), methotrexate and prednisone. Improvement of systemic symptoms, right heart catheterization (RHC) findings and the VECTRA-DA score served as a measure of treatment response. Tocilizumab has been effective in demonstrating marked improvement in both the clinical and laboratory parameters. Tocilizumab is an effective novel treatment for AOSD with PAH. This is the first documented report of successful use of tocilizumab in AOSD patients presenting with PAH. Prospective comparative studies could help validate its efficacy and safety.

Life-threatening complications of adult-onset Still's disease.

Adult-onset Still's Disease (AOSD) since its description in 1971 has proven to be a very complex and challenging disease entity. This rare auto-inflammatory disease is classically described by the "Still's triad" of fever, rash, and arthritis, although the atypical cases frequently outnumber the typical ones. The exact pathogenesis and etiologic factors responsible for the clinical features remain largely obscure, despite recent suggestive cytokine biology findings. Diagnosis is made on clinical grounds, following the exclusion of mimickers of infectious, autoimmune or neoplastic etiology, with the additional consideration of non-specific laboratory abnormalities such as peripheral leukocytosis and elevation of serum ferritin and other acute phase reactants. The disease manifestations are protean and can include diverse complications, affecting multiple organ systems. Moreover, the severity of the organ involvement can vary considerably, representing a wide spectrum from the self-limited to severe. The mainstay of therapy has evolved from the traditional use of corticosteroids and oral immunosupressants to the newer targeted treatments with biologic agents. The scope of this review is to alert the clinician to the existence of life-threatening AOSD complications, namely the macrophage activation syndrome, disseminated intravascular coagulopathy, thrombotic thrombocytopenic purpura, diffuse alveolar hemorrhage, and pulmonary arterial hypertension. Such knowledge may lead in earlier recognition, prompt treatment, and, ideally, improved patient outcomes.

Can traumatic injury trigger psoriatic arthritis? A review of the literature.

Traumatic injury as a trigger for the subsequent development of psoriatic arthritis (PsA) has been implicated by several case reports and case series. However, it is still unclear whether trauma is the inciting event or just an incidental finding. It is thought that the interplay of genetic, immunologic, and environmental factors, such as trauma, may trigger the development of PsA. At least two hypotheses of how trauma may be linked to the development of PsA have surfaced and involve a "deep Koebner effect," the concept of a synovio-entheseal complex and activation of the innate immune system by biomechanical factors. The role of neuropeptides such as substance P and vasoactive intestinal peptide has been highlighted in the synovium after trauma. Better understanding of this phenomenon would shed light into the pathophysiology of Psa and help the development of preventive and therapeutic strategies.