Placebo and nocebo effects are known to play a key role in treatment effects in a wide variety of conditions. These effects have frequently been investigated with regard to pain and also in other physical sensations, but have hardly been investigated with regard to itch. In addition, neither in pain nor in any other physical sensation, the single and combined contribution of the expectancy mechanisms of conditioning and verbal suggestion have ever been investigated in both placebo and nocebo effects within one design. For the first time, the role of verbal suggestion and conditioning in placebo and nocebo effects on itch was experimentally investigated. Expectations about itch stimuli were induced in healthy subjects by verbal suggestion, conditioning, or a combination of both procedures, and compared with a control group without expectation induction. Itch was induced electrically by means of quantitative sensory testing. Significant placebo and nocebo effects were induced in the group in which combined procedures of conditioning and verbal suggestion were applied in comparison with the control group. The conditioning and verbal suggestion procedures applied individually did not induce significant placebo and nocebo effects when compared with the control group. The results of this study extend existing evidence on different physical sensations, like pain, by showing that also for itch, the combination of conditioning and verbal suggestion is most promising in inducing both placebo and nocebo effects. More research on placebo and nocebo effects at a perceptive and neurobiological level is warranted to further elucidate the common and specific mechanisms underlying placebo and nocebo effects on itch and other physical sensations.

Physical complaints, such as pain, can be effectively reduced by placebo effects through induction of positive expectations, or increased by nocebo effects through induction of negative expectations. In the present study, verbally induced nocebo and placebo effects on itch were experimentally investigated for the first time. In part 1, the role of verbal suggestions in inducing nocebo effects on itch and pain was investigated. All subjects received the same somatosensory quantitative sensory testing stimuli, that is, mechanical and electrical stimuli and application of histamine, and verbal suggestions to manipulate expectations regarding the stimuli. The suggestions were designed to produce either high expectations for itch (itch nocebo) or pain (pain nocebo) or low expectations for itch (itch nocebo control) or pain (pain nocebo control). Results showed that high itch and pain expectations resulted in higher levels of itch and pain, respectively. When comparing nocebo effects, induced by verbal suggestions, results were more pronounced for itch than for pain. In part 2, verbal suggestions designed to produce a placebo effect on itch (itch placebo) or pain (pain placebo), or neutral suggestions (itch placebo control and pain placebo control) were given regarding a second application of histamine and compared with the first application applied in part 1. Results of placebo effects only showed a significantly larger decrease in itch in the itch placebo condition than in the pain placebo condition. In conclusion, we showed for the first time that nocebo and possibly placebo responses can be induced on itch by verbal suggestions.

It is well known that the genital skin may be affected by psoriasis. However, little is known about the prevalence and clinical appearance of genital psoriasis, and genital skin is often neglected in the treatment of psoriatic patients. We performed an extensive systematic literature search for evidence-based data on genital psoriasis with respect to epidemiology, aetiology, clinical and histopathological presentation, diagnosis and treatment. Three bibliographical databases (PubMed, EMBASE and the Cochrane Library) were used as data sources. Fifty-nine articles on genital psoriasis were included. The results show that psoriasis frequently affects the genital skin, but that evidence-based data with respect to the efficacy and safety of treatments for genital psoriasis are extremely limited. An advised treatment paradigm for genital psoriasis, based on the levels of evidence, is: first-line: (weak) topical corticosteroids; second-line: vitamin D preparations or tar-based treatments.

Nearly three-quarters of patients with moderate-to-severe psoriasis receiving etanercept 50 mg QW achieved significant improvement in disease severity over 24 weeks. This study also showed a favourable tolerability and safety profile with etanercept 50 mg QW.

Visible blue light, as given in the present study, does not cause deoxyribonucleic acid damage or early photo-ageing. The biological effects of blue light on normal skin are transient melanogenesis and inexplicable vacuolization without resulting apoptosis. In conclusion, the (short-term) use of visible blue light in dermatological practice is safe.

Clinical trials successfully using antibodies targeting IL-17 in psoriasis support the importance of IL-17 in the pathophysiology of this disease. However, there is a debate concerning the source and dynamics of IL-17 production in inflamed skin. Here we characterized IL-17-producing immune cells over time, using two established in vivo models of human skin inflammation that share many histological features with psoriasis, i.e., leukotriene B4 application and tape-stripping. Both treatments revealed a clear influx of neutrophils and T cells. Staining for IL-17 revealed that the majority of IL-17 was expressed by neutrophils and mast cells, in both models. Neutrophils, but not mast cells, coexpressed the IL-17-associated transcription factor RORγt and were able to form extracellular traps. While the presence of mast cells remained steady during the skin inflammatory process, the presence of neutrophils was clearly dynamic in time. Therefore, it is attractive to hypothesize that IL-17+/RORγt+ neutrophils contribute to human skin inflammation in vivo and possibly to the pathogenesis of skin diseases such as psoriasis. Surprisingly, T cells represented a minority of the IL-17-expressing cell population. These observations challenge the classical opinion that IL-17 is predominantly associated with T cells in skin inflammation.

Psoriasis is a common chronic inflammatory skin disease that results from interplay between the immune system and the epithelium. In the light of very successful anticytokine therapies for psoriasis, the focus has been directed towards the adaptive immune system. Expression studies, genetic studies and treatments specifically targeting players of the IL-23/IL-17 pathway, point at an important role for IL-17 in the pathogenesis of psoriasis. IL-17 stimulates the keratinocytes to produce psoriasis-associated molecules, eventually leading to chronic skin inflammation. The current opinion is that IL-17 is mainly produced by T cells, so-called T-helper 17 (Th17) cells, in psoriasis. However, evidence is accumulating that cells of the innate immune system, like neutrophils, mast cells, cd T cells and innate lymphoid cells are the main source of IL-17 in psoriasis, rather than T cells. The paradigm in this field of research is shifting. With this viewpoint article, we will address this novel concept by critically summarizing the current literature on this subject. In psoriatic arthritis and atherosclerosis, important conditions related to psoriasis, it was also found that the majority of IL-17 is associated with cells of the innate immune system. This new concept changes our view of IL-17. Blocking IL-17 with targeted treatments might be more far-reaching than previously thought; not only IL-17 production by T cells but also by innate immune cells is blocked. Furthermore, therapies specifically targeting IL-17 may not only improve psoriasis, but also comorbidity that is associated with the IL-17 pathway, hereby preventing serious complications on the long term.

IMPORTANCE Biologics revolutionized the treatment of psoriasis. Biologics are given in a fixed dose, but lower doses might be possible. OBJECTIVE To investigate whether dose reduction (DR) of biologics in patients with stable psoriasis is noninferior to usual care (UC). DESIGN, SETTING, AND PARTICIPANTS This pragmatic, open-label, prospective, controlled, noninferiority randomized clinical trial was conducted from March 1, 2016, to July 22, 2018, at 6 dermatology departments in the Netherlands. A total of 120 patients with plaque psoriasis and stable low disease activity who were receiving treatment with adalimumab, etanercept, or ustekinumab were studied. INTERVENTIONS Patients were randomized 1:1 to DR (n = 60) or UC (n = 60). In the DR group, injection intervals were prolonged stepwise, leading to 67% and 50% of the original dose. MAIN OUTCOMES AND MEASURES The primary outcome was between-group difference in disease activity corrected for baseline at 12 months compared with the predefined noninferiority margin of 0.5. Secondary outcomes were Psoriasis Area and Severity Index (PASI) score and health-related quality of life (including Dermatology Life Quality Index [DLQI] and Medical Outcomes Study 36-Item Short Form Health Survey scores), proportion of patients with short and persistent flares (defined as PASI and/or DLQI scores >5 for Ն3 months), and proportion of patients with successful dose tapering. RESULTS Of 120 patients (mean [SD] age, 54.0 [13.2] years; 82 [68%] male), 2 patients were lost to follow-up, 2 patients had a protocol violation, and 5 patients had a protocol deviation, leaving 111 patients for the per-protocol analysis (53 in the DR group and 58 in the UC group). The median PASI scores at month 12 were 3.4 (interquartile range [IQR], 2.2-4.5) in the DR group and 2.1 (IQR, 0.6-3.6) in the UC group (mean difference, 1.2; 95% CI, 0.7-1.8). This indicates that noninferiority was not demonstrated for DR compared to UC. The median DLQI score at month 12 was 1.0 (IQR, 0.0-2.0) in the DR group and 0.0 (IQR, 0.0-2.0) in the UC group (mean difference, 0.8; 95% CI, 0.3-1.3), indicating noninferiority for DR compared with UC. No significant difference was found regarding persistent flares between groups (n = 5 in both groups). Twenty-eight patients (53%; 95% CI, 39%-67%) in the DR group tapered their dose successfully at 12 months. No severe adverse events related to the intervention occurred. CONCLUSIONS AND RELEVANCE In this trial, noninferiority was not demonstrated for DR of adalimumab, etanercept, and ustekinumab based on the PASI in patients with psoriasis compared with UC with the chosen noninferiority margin. However, the strategy was noninferior based on the DLQI. Dose tapering did not lead to persistent flares or safety issues.