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Psoriasis is a common, chronic, inflammatory disease that can result in decreased quality of life. Clinicians have long been vexed by this ancient affliction. Although most medical literature prior to Willan (1757-1812) lumped psoriasis, leprosy, eczema, and other inflammatory dermatoses into a confusing menagerie, Celsus gave a convincing account of psoriasis vulgaris almost 2000 years ago. His description included many of the morphologic features that physicians today utilize to diagnose psoriasis, including the "ruddy" or salmon-colored plaques with silvery scales that often are associated with punctate hemorrhage or "erosions" when removed.1
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More than 7.5 million adults (2.1% of the population) in the United States are affected and 30% of these individuals will develop psoriatic arthritis.2 About 1.5 million of them are considered to have moderate to severe disease. Psoriasis may have a significant negative impact on a patient's quality of life. Patient often are self-conscious, depressed, or frustrated over the appearance of their skin.
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Psoriasis spans all socioeconomic groups, and its prevalence varies by geographic location. Historically, the disease is more common in the northern latitudes. The rate of psoriatic disease is lower in African Americans compared with that in European Americans.2
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The primary cause of psoriasis is a dysregulation of the cell-mediated, adaptive immune response. This dysregulation is likely triggered by hyperactivity of the innate immunological surveillance system to environmental antigens. In genetically predisposed individuals, the Th1 pathway response is overstimulated. This overproduction of Th1-related cytokines along with IL-12, 17, and 23 causes hyperproliferation of epidermal keratinocytes. These events lead to the formation of the psoriatic plaques.3
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Environmental factors and disease states that interact with polygenic inheritance patterns most likely account for the variable expression of psoriatic disease. These include streptococcal pharyngitis (guttate psoriasis), stressful life events, low humidity, human immunodeficiency virus (HIV), trauma, medications, cold, and obesity. Diets high in fish oils seem to be protective against the development of psoriasis.2,4
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Clinical Presentation
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Most patients with mild to moderate psoriasis are asymptomatic, but pruritus is common in severe or widespread disease. Patients may also give a history of joint pain and swelling, especially in the fingers and toes.
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Psoriasis can vary in appearance and distribution. However, there are clues in the physical examination that allow the clinician to properly diagnose psoriasis and identify its subtypes.
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Plaque-type psoriasis vulgaris accounts for 90% of all cases. The primary lesion is a scaly, red- to salmon-pink-colored papule that expands centrifugally to form a similarly colored plaque (Figure 9-1). It is usually covered by a white or silvery scale that, when removed, may show pinpoint bleeding (Auspitz sign). Its border may be red and with time central clearing may occur, with the plaques taking on an annular or arcuate configuration. Plaque-type psoriasis is classically an extensor disease often involving the knees, elbows (Figure 9-2), gluteal cleft, lumbosacral region, and the umbilicus. Psoriasis may involve the scalp (Figure 9-3). Psoriatic plaques may occur in an area after trauma, pressure, or injury. This is known as the Koebner phenomenon.
Inverse psoriasis presents with thin pink plaques with minimal scale in the axillae (Figure 9-4), inguinal and inframammary area, and body folds of the trunk. It may occur in conjunction with typical plaque psoriasis or it may be the only manifestation of psoriasis.
Guttate psoriasis occurs in less than 2% of cases, but it is a common psoriatic subtype in young adults. It is characterized by small "droplet-like" thin pink to salmon-colored papules and plaques surmounted by a fine white scale (Figure 9-5). The distribution is often similar to that of classic pityriasis rosea, favoring the trunk, abdomen, and upper thighs and fading toward the acral surfaces and sparing the palms and soles.
Pustular psoriasis (von Zumbusch) is an acute variant of the disease that presents with small, monomorphic sterile pustules surmounting painful, inflamed, erythematous papules. Fever, systemic symptoms, and an elevated white blood cell count often accompany generalized pustular psoriasis. Acral pustules, usually without systemic symptoms, characterize palmoplantar pustulosis (Figure 9-6), which is a milder, but more common presentation of pustular psoriasis.
Erythrodermic psoriasis is a skin reaction pattern of total body redness and desquamation of the skin. There are many causes of erythroderma and it is not specific to psoriasis. The massive shedding of skin that occurs during an erythrodermic flare of psoriasis can result in infection, hypothermia, protein loss, hypoalbuminuria, dehydration, and electrolyte disturbances.4
Psoriatic nails can be seen in up to 50% of patients with psoriasis. It may be the only manifestation of psoriasis. It is recognized that nail disease is more closely linked with psoriatic joint disease. Up to 90% of patients with psoriatic arthritis have nail disease.4 Nail dystrophies associated with psoriasis include pitting, onycholysis (nail plate separation), oil spots (yellow-orange subungual discoloration), thickening, and subungual debris (Figure 20-3). Splinter hemorrhages may also be present.
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Blood work is generally not necessary to make a diagnosis of psoriasis. Pustular flares of psoriasis during pregnancy may be associated with hypocalcemia. A biopsy is often helpful if the diagnosis is unclear. A punch biopsy of a plaque or pustule often supports the diagnosis. A biopsy is warranted in any patient not responding as expected to traditional therapy. The microscopic findings of common plaque-type psoriasis are epidermal hyperplasia, parakeratosis, thinning of the granular layer, epidermal infiltration of neutrophils, and occasional "Munro abscesses" (intraepithelial collections of neutrophils).
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The key diagnostic clinical features of psoriasis are red to pink plaques with silvery white scale on the elbows, knees, scalp, and lower back and legs.
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Differential Diagnosis
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Topical steroids are the first-line treatment of mild to moderate psoriasis. They act as a foundation on which to build a therapeutic regimen for more severe disease. While topical regimens demonstrate efficacy in clinical trials, the response to these agents in everyday practice is often variable. Frequently, this is a result of poor compliance. Ointments are the most effective vehicles for psoriasis, but they stain clothing and bedding. Creams are better patient-accepted vehicles for the face, neck, and hands. Solutions and foams are appropriate for the scalp. Table 9-2 contains commonly used topical medications for psoriasis.
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It is often advisable to begin therapy with one simple agent. In plaque-type psoriasis, superpotent topical steroids, such as clobetasol or betamethasone, are usually necessary to treat thick plaques.4 Scalp disease requires ultrapotent steroids in solution or foam vehicles. A simple regimen utilizing clobetasol or betamethasone twice a day for 2 to 4 weeks is an easy way to achieve efficacy. With time, the patient can move to an alternating regimen of vitamin D analogues, such as calcipotriol (calcipotriene) or calcitriol. These medications can be alternated by day (calcipotriol Monday to Thursday and clobetasol Friday to Sunday) or by application (calcipotriol in morning and clobetasol at bedtime). Topical vitamin D analogues may cause hypercalcemia; therefore, the weekly dose should be under 100 mg. A less potent topical steroid and more cost-effective agent such as triamcinolone, when utilized regularly, may be more effective than higher potency steroids. After finding the preferred vehicle and topical regimen for a patient, closely spaced follow-up visits improve adherence and will give the clinician opportunity to encourage continued compliance, and fine-tune the regimen based on the patient's condition.
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In areas of thin skin such as the face, neck, axillae, groin, genitals, and body folds, lower potency steroids such as hydrocortisone 2.5%, desonide, and hydrocortisone valerate 2.5% are useful.5 Vitamin D analogues such as calcipotriene have traditionally not been used in these areas due to their tendency to cause inflammation.
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Topical calcineurin-inhibiting agents are also quite useful for therapy of psoriasis.6 Tacrolimus ointment (0.1% for adults, 0.03% for children) may burn a bit on application, but seems to have slightly more efficacy than topical pimecrolimus. Because these medications are not corticosteroids, they do not cause skin atrophy, glaucoma, or many other steroid-related side effects. Thus, they are an effective, safe way to treat psoriasis on the face, in the skin folds, and around the eyes. In the United States these medications are Food and Drug Administration (FDA) approved only for atopic dermatitis and carry a black box warning for lymphoma.
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Tazarotene (gel or cream, 0.05% or 0.1%) is a retinoid. It can be used as a steroid-sparing agent in a manner similar to the vitamin D analogues. This agent tends to cause more inflammation than calcipotriene. Therefore, patients may find that tazarotene fits best into their regimen when applied in conjunction with topical steroids. Tazarotene is in pregnancy category X.
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In the setting of hyperkeratotic, scaly plaques there may be a role for keratolytics to remove scale and facilitate penetration of the topical steroid and/or vitamin D analogue. Salicylic acid, urea, and lactic acid are agents that can be added to a regimen for this purpose. Salicylic acid comes as a cream, gel, cream, or shampoo in concentrations that range from 2% to 10%.
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Topical coal tar products have an anti-inflammatory effect in psoriasis and can be used in conjunction with topical steroids and keratolytic agents. Examples of tar products include Estar, Fototar, PsoriGel, and Neutrogena T/Derm Tar Emollient.
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Emollients may aid treatment of psoriasis. They can improve efficacy and lower the economic burden of other topical agents by softening the stratum corneum through hydration and reduction of superficial scale. A daily bath in warm water, followed by application of petrolatum and supplemented by 2 or 3 further applications of a moisturizer during the day, is a beneficial addition to any treatment regimen.4
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There is a dearth of evidence regarding treatment of psoriatic disease in children. The lack of good, double-blinded, placebo, controlled trials is not specific to psoriasis treatment, but it does make foretelling the future consequences of one's therapeutic decisions in this population quite difficult. Most of the principles discussed above with regard to adults still hold for the pediatric population. In the pediatric population one must, of course, consider long-term side effects due to lengthy exposure to immunomodulators.
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Every patient with psoriasis should be specifically screened for joint disease and enthesitis (inflammation of the tendon insertions).4 History of morning stiffness, joint tenderness, swelling, sausage digits, and involvement of the peripheral small joints is characteristic. The hands are the most common site of involvement. Enthesitis usually occurs at the insertion sites of the Achilles tendon, the plantar fascia, and ligamentous attachment points of the rib, spine, and pelvis. Musculoskeletal involvement can present at any time, but most often between the ages of 30 and 50 years.
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Comorbidities in Patient with Psoriasis
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Psoriasis is an independent risk factor for atherosclerosis, coronary artery disease, myocardial infarction, stroke, and cardiovascular mortality. Patients with psoriasis are more likely to have other cardiovascular risk factors such as diabetes, hypertension, dyslipidemia, tobacco use, and obesity.4,7
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Potential Causes of Flares of Psoriasis
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Group A beta-hemolytic streptococci infection can act as an environmental trigger for guttate psoriasis particularly in the pediatric population.4 Many clinicians will obtain an antistreptolysin-O, antihyaluronidase, anti-DNase-B, and streptozyme titer along with streptococcal cultures of the throat and perianal area as part of the initial workup of pediatric psoriasis. Other commensal organisms on the skin may play a role in specific variants of psoriasis. Management of these microbes can be an adjunct to psoriatic treatment.
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Common medications that may exacerbate psoriasis include beta-blockers, ACE inhibitors, nonsteroidal anti-inflammatory drugs, lithium, interferon, and antimalarials.4 Systemic corticosteroids, although providing short-term benefit in control of psoriasis, are not recommended. Abrupt discontinuation of the drug commonly exacerbates the disease.
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Psychiatric comorbidities such as anxiety and depression may exacerbate psoriasis. Stress is also common trigger of psoriasis.3 Thus, psoriatic patients may benefit from psychological intervention.
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Indications for Consultation
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Dermatological consultation is indicated when topical medications have not been effective and ultraviolet light or systemic therapy are needed. These therapies include office- or home-based narrow-band ultraviolet B or A light therapy, light therapy with psoralens (PUVA), Goeckerman therapy (light therapy with tar), acitretin, methotrexate, biologics (etanercept, adalimumab, alefacept, infliximab, ustekinumab, golimumab, etc), and cyclosporine.8
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Pregnant or lactating women with psoriasis should be comanaged by obstetrics and dermatology.9
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All systemic comorbidities should be monitored and discussed with patients, with consultation to specialists when appropriate as discussed above. Rheumatologic consultation is indicated if signs or symptoms of psoriatic joint disease or enthesitis are present.
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