Psoriasis is a hereditary disorder that affects 3% of the population worldwide [1] - [3] . There are two common ages for the onset of psoriasis. The first is around 21 years and the second at approximately 50 years [4] [5] . The most frequent type is psoriasis vulgaris, which appears as chronic, erythematous (reddish), and scaling skin lesions [6] . Clinical presentation varies from those with only a few localized lesions to those with generalized skin involvement [4] .

There is evidence indicating that interaction between genes and certain environmental factors is an important cause of this disease [7] . Inflammatory cytokines such as tumor necrosis factor alpha, interferon gamma, and other type 1 cytokines also play an important role in the pathogenesis of psoriasis [8] . Many drugs that are used to treat other clinical conditions have also been reported to be responsible for the onset or exacerbation of psoriasis [9] . Among these drugs are lithium salts, antimalarials, beta-blocking agents, non-steroidal anti-inflam- matory drugs (NSAIDS), angiotensin-converting enzyme (ACE) inhibitors, and the withdrawal of corticosteroids [10] [11] .

Many clinical variants to the psoriasis are described, such as psoriasis vulgaris, guttate psoriasis (drops psoriasis), erythrodermic psoriasis (red psoriasis) and pustular psoriasis [11] [12] . The scalp is one of the most commonly affected parts of the body in people with psoriasis, and the frequency of involvement increases with the duration of the disease [13] . It may be part of generalized psoriasis or coexist with isolated plaques, or the scalp may be the only site involved. Signs and symptoms of scalp psoriasis vary significantly in different people, but pruritus, scaling and cosmetic embarrassment are often present [14] [15] . Because sensitive facial skin is so near the scalp, the use of potentially irritating topical treatments may be limited. Even so, the specific challenges of scalp psoriasis are often neglected in treatment guidelines [15] [16] .

Scalp psoriasis can occasionally be confused with seborrhoeic dermatitis affecting the scalp [17] . Seborrhoeic dermatitis is another inflammatory condition which commonly affects the whole of the scalp resulting in mild inflammation and dandruff [17] . Psoriasis on the other hand is usually well-demarcated and has a coarser scale, but early diffuse psoriasis of the scalp can sometimes look very similar to seborrhoeic dermatitis. Sometimes a scalp biopsy may help [18] [19] . Those with psoriasis may also suffer from psychological distress, especially as a result of stigmatization and self-consciousness, so relatively high rates of depression have been reported [20] .

The Psoriasis Area and Severity Index (PASI) is one of the most frequently used instruments to evaluate the severity of the disease and its response to different treatments, and its use is based on the extension and severity of the impact on the skin’s surface [21] [22] .

Relevant aspects of psoriasis that affect the person with this disease are evaluated using a variety of instruments, including the Psoriasis Disability Index (PDI) [23] , Dermatology Quality of Life Index (DLQI) [24] , the Psoriasis Symptom Assessment [25] , and the Itching Scale [26] . The Physician Global Assessment is a tool to evaluate the psoriatic plaques [27] . This is a seven-point scale, with 7 being clear and 6 almost clear, 5 mild, 4 mild to moderate, 3 moderate, 2 moderately severe and 1 being severe psoriasis.

The aim of this review is to evaluate the topical treatments for scalp psoriasis compared with placebos.

The electronic search found in PubMed 239 articles, in Embase, 39 articles and in the Cochrane Library, 125 articles. No article was found in the search of LILACS. Fifteen placebo-controlled studies were selected. The flowchart used in the selection of the papers discussed in this review is show in Figure 1.

The 15 studies included 3441 patients. The patient age was between 12 and 97 years old. Gender data were mentioned in 10 of the 15 studies included (66%). Patients were mostly female (1934 women and 1691 men). Twelve studies have discussed about the severity of psoriasis. In these studies that the severity has been described, the classification of severity was mild (0 study), mild to moderate (one study), moderate to severe (11 studies) and severe (0 trial). However, four studies did not provide sufficient information to assess the clinical severity. The evaluation score most widely used to assess the clinical severity was the GSS-TSS (global-total severity score). Quality of life was also mentioned.

The duration of treatment ranged from two weeks to two months. The evaluation included Individual signs (erythema, scaling, and thickening) and Total score or global severity (TSS or GSS).

Concerning to the randomized controlled trials, among the fifteen selected publications, 8 studies (53%) reported clearly the method used for randomization and 3 studies (20%) used the computer randomization. Related to the anthropometric characteristics of participants used in the studies selected, as the age and gender, six studies (40%) provided data regarding age, gender and characteristics of clinical patients. Eight studies (53%) provided incomplete data. Eight studies were excluded. One study was not considered due to it did not provide data properly. Seven studies were excluded because there was no comparison with placebo.

In Table 1 are shown the selected publications, the treatments suggested involving medication and placebo, and the conclusion of the studies.

Van Voorhees and Fried, 2009 [44] have pointed out that the involvement of the scalp in patient with psoriasis is frequent. Due to the greater exposure to the environmental, it has a considerable effect on the quality of life of

the patient. In this case, nevertheless, this fact must be discussed, due to the published studies rarely use tools to address these issues. Zampieron et al., 2015 [45] have also reported that patients with scalp psoriasis suffered from a lower quality of life relating to the highly visible site of their psoriatic lesions. In consequence this fact stimulates investigations with this dermatologic disease, as it is presented in our work.

Firstly 403 papers were found in the databases that were searched. However, the analysis of the available papers used in this review included only 15 randomized controlled trials (see flowchart in Figure 1) due to the inclusion and exclusion criteria use.

The number of participants with scalp psoriasis with topical treatment in the publications is more than three thousand. The selected papers involve a total of 3 441 patients. Each of the studies utilized a comparison with a placebo, and the results of active ingredients were found to be more statistically significant than the placebos.

Many topical treatments, such as corticosteroids, calcipotriol, coal tar, salicylic acid are used for scalp psoriasis [46] . But, it is necessary to verify that there are few adequately controlled investigations that support the effectiveness of the suggested topical managements.

On the basis of the findings of this review, it was found that the best results were obtained with the use of clobetasol propionate in different vehicles (solution, foam and lotion) [29] [30] . When the placebo was compared to calcipotriol, there were better results with calcipotriol [47] - [49] ; however, the magnitude of the effect was lower than in relation to clobetasol and It was similar to other corticosteroids, such as valerate of betame- thasone, ancinonide, halcinonide, and fluocinolone acetonide. The opposite was observed for psoriasis on the body, which is described a greater efficiency in the association between calcipotriol and betamethasone dipropionate [50] . This study found no effect in terms of the overall gain in response to treatment in cases of psoriasis of the scalp. In Table 1, it is possible finding suitable information about the different formulations used to treat scalp psoriasis and the type of vehicle.

Characteristically, psoriasis is recurrent over years, and maintenance of the controlled disease, is a clinical challenge [51] . This fact is also true for scalp psoriasis. In this study, Meredith and Ormerod, 2012 [51] reported

that it was not possible to assess recurrence rates because there was only a short period of follow up.

It is important to state that is often necessary to combine oral treatments and topicals, especially in severe cases of scalp psoriasis, there are, extensive or resistant to topical treatments. In these cases, some authors have pointed out the importance of medications, such as methotrexate, cyclosporine, acitretin, and treatment involving psoralen plus ultraviolet A (PUVA) [52] - [55] .

Vergou et al., 2011 [56] have also suggested immunobiologicals, including infliximab, adalimumab and the etarnecept to be administered. For this class of drugs, a complete healing of the lesions and maintenance of the healing period of three years for adalimumab treatment has been described [57] .

Psoriasis of the scalp, especially those cases classified as moderate to severe is associated with emotional and social disorders that affect the well-being of patients [58] . Despite this, few studies evaluate the emotional repercussions of this type of psoriasis patients. The National Psoriasis Foundation 2006 Benchmark Survey estimates that psoriasis has a moderate to large negative impact on quality of life (QoL) in approximately 75% of affected patients [59] . It is also noted that those patients are more likely to commit suicide when compared to those who do not have the disease [20] [60] .

Adverse effects were found in 9 of 15 studies. Studies generally omit reporting adverse events. Due to the small sample of studies and the short follow-up period, ranging from two weeks to two months, the possibility of not detecting more serious adverse events or consequence of the chronic use of medications may be higher than they would be under other conditions.

In conclusion, this investigation demonstrates the efficacy of topical treatments for scalp psoriasis, such as corticosteroids, calcipotriol, ciclopirox olamine, and associations, when compared with placebos. Clobetasol propionate (0.05%) was the most active ingredient, in various vehicles, in terms of the induction treatment of psoriasis of the scalp. However, due to the small clinical follow-up time of the studies, it was not possible to obtain data concerning the maintenance of the outcome or recurrence rates, so more research is needed in this area. It is important to consider that among the active principles used for the topical treatment of scalp psoriasis and compared with placebo, clobetasol propionate was the most effective, in all types of vehicle.

The authors thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (National Counsel of Technological and Scientific Development) for the support.

There is no conflict of interest in this paper.