Psoriasis is an immune-mediated genetic skin disease. The underlying pathomechanisms involve complex interaction between the innate and adaptive immune system. T cells interact with dendritic cells, macrophages, and keratinocytes, which can be mediated by their secreted cytokines. In the past decade, biologics targeting tumor necrosis factor-α, interleukin (IL)-23, and IL-17 have been developed and approved for the treatment of psoriasis. These biologics have dramatically changed the treatment and management of psoriasis. In contrast, various triggering factors can elicit the disease in genetically predisposed individuals. Recent studies suggest that the exacerbation of psoriasis can lead to systemic inflammation and cardiovascular comorbidity. In addition, psoriasis may be associated with other auto-inflammatory and auto-immune diseases. In this review, we summarize the risk factors, which can be divided into two groups (namely, extrinsic and intrinsic risk factors), responsible for the onset and exacerbation of psoriasis in order to facilitate its prevention.

The HLA-Cw6 antigen has been associated with psoriasis vulgaris despite racial and ethnic differences. However, it remains unclear whether it is the HLA-Cw6 antigen itself or a closely linked, hitherto unidentified, locus that predisposes to the disease. Here, in order to map the susceptibility locus for psoriasis vulgaris precisely within the HLA class I region, 11 polymorphic microsatellite markers distributed throughout a 1060 kb segment surrounding the HLA-C locus were subjected to association analysis in Japanese psoriasis vulgaris patients. Statistical analyses of the distribution and deviation from Hardy-Weinberg equilibrium of the allelic frequency at each micro-satellite locus revealed that the pathogenic gene for psoriasis vulgaris is located within a reduced interval of 111 kb spanning 89-200 kb telomeric of the HLA-C gene. In addition to three known genes, POU5F1, TCF19 and S, this 111 kb fragment contains four new, expressed genes identified in the course of our genomic sequencing of the entire HLA class I region. Therefore, these seven genes are the potential candidates for susceptibility to psoriasis vulgaris.

This is a Japanese retrospective single‐center study carried out between 1 January 2010 and 21 November 2018 at the Department of Dermatology in Jichi Medical University Hospital. The drug survival rate for six biologic agents used for the treatment of psoriasis was investigated. We reviewed the clinical records of 315 treatment series of 205 patients with moderate to severe psoriasis treated with adalimumab (103 cases), infliximab (70 cases), ustekinumab (66 cases), secukinumab (38 cases), brodalumab (12 cases) and ixekizumab (26 cases). In our study, ustekinumab revealed a trend towards higher drug survival among the six biologic agents. Ustekinumab had a higher drug survival rate than infliximab and secukinumab with significant differences by log–rank test among all patients and among biologic‐naive (bio‐naive) patients. There was no significant difference in drug survival between bio‐naive and biologic‐experienced (non‐naive) patients in the treatment courses with adalimumab, infliximab, ustekinumab, secukinumab and ixekizumab. The dose augmentation therapy in infliximab‐treated patients was associated with longer drug survival. Of all patients, 25 cases with generalized pustular psoriasis (GPP) were included, who functioned as the negative predictor for drug persistence with a hazard ratio of 1.87 (95% confidence interval, 1.12–3.11; P = 0.016). Our results reveal that ustekinumab had a superior drug survival, which is supported by the previous studies. Further studies are needed to clarify the efficacy of biologic agents on patients with GPP.

Apremilast is a novel oral phosphodiesterase‐4 inhibitor approved for treatment of plaque psoriasis and psoriatic arthritis in Japan in December 2016. We have treated a substantial number of patients with psoriasis with apremilast and investigated the length of the treatment period with apremilast (drug survival of apremilast) in 138 patients with psoriasis who were treated at the Department of Dermatology in Jichi Medical University Hospital from 1 March 2017 to 31 August 2018 using the Kaplan–Meier survival curve. The drug survival rate of apremilast at 1 year was 53.4%. The median length of the drug survival period was 453 days. There were no statistical differences in the drug survival rate in terms of the type of psoriasis, previous systemic treatment or presence of one or more adverse events. Drug efficacy was investigated in 115 patients who were followed for more than 16 weeks. There was no correlation between drug efficacy and sex, previous systemic treatment or presence of one or more adverse events; however, there was a correlation between drug efficacy and plaque size (P < 0.01, rs = −0.29). The result of our study indicates that apremilast is effective regardless of the history of prior systemic treatment, and it supports our previous finding that small plaque‐type psoriasis is more sensitive to treatment with apremilast.

Apremilast is a novel oral phosphodiesterase 4 inhibitor effective for psoriasis. It regulates the production of pro-inflammatory mediators. Apremilast was approved in December 2016 in Japan; however, its efficacy and safety in a real-world setting among Japanese patients have not been reported. We report on 44 patients treated with apremilast between March and October 2017. The median treatment duration was 25 weeks (range, 2-33). Thirty-five patients (79.5%) continued the drug for at least 23 weeks, and five (11.4%) achieved a Psoriasis Area and Severity Index 100 response within 12 weeks. Nine patients discontinued the drug within 24 weeks mainly due to insufficient efficacy (n = 3) and adverse events (n = 4). Seven patients continued their previous systemic therapies such as cyclosporin (n = 1), methotrexate (n = 1), etretinate + methotrexate (n = 1) and biologics (n = 4) combined with apremilast. Of these patients, 55.9% had at least one adverse event although no severe adverse events. The most common adverse event was diarrhea (31.8%), followed by nausea (25.0%), headache (13.6%), abdominal discomfort (6.8%) and vomiting (6.8%). The proportion of diarrhea in our patients was higher than those of previous clinical trials. Among 10 patients with psoriatic arthritis, apremilast did not improve joint pain in nine (90%). To investigate the relationship between treatment efficacy and plaque size, we defined a small plaque as an individual rash diameter of 1 inch or less. The efficacy of apremilast was greater in patients with small plaques than in patients with large plaques.