6-11: Psoriasis

Psoriasis is a common benign, chronic inflammatory skin disease with both a genetic basis and known environmental triggers. Injury or irritation of normal skin tends to induce lesions of psoriasis at the site (Koebner phenomenon) (eFigure 6–15). Obesity worsens psoriasis, and significant weight loss in obese persons may lead to substantial improvement. Psoriasis has several variants—the most common is the plaque type (eFigure 6–13) (eFigure 6–16). Eruptive (guttate) psoriasis consisting of myriad lesions 3–10 mm in diameter occurs occasionally after streptococcal pharyngitis. Rarely, life-threatening forms (generalized pustular and erythrodermic psoriasis) may occur.

There are often no symptoms, but itching may occur and be severe. Favored sites include the scalp, elbows, knees, palms and soles, and nails. The lesions are red, sharply defined plaques covered with silvery scale (Figure 6–7). The glans penis and vulva may be affected. Occasionally, only the flexures (axillae, inguinal areas) are involved (termed inverse psoriasis). Fine stippling (“pitting”) in the nails is highly suggestive of psoriasis (Figure 6–8) (eFigure 6–17) as is onycholysis. The combination of red plaques with silvery scales on elbows and knees, with scaliness in the scalp or nail findings, is diagnostic. Patients with psoriasis often have a pink or red intergluteal fold. Not all patients have findings in all locations, but the occurrence of a few may help make the diagnosis when other lesions are not typical. Some patients have mainly hand or foot dermatitis and only minimal findings elsewhere. There may be associated arthritis that is most commonly distal and oligoarticular, although the rheumatoid variety with a negative rheumatoid factor may occur. The psychosocial impact of psoriasis is a major factor in determining the treatment of the patient.

Psoriasis lesions are well demarcated and affect extensor surfaces—in contrast to atopic dermatitis, with poorly demarcated plaques in flexural distribution (eFigure 6–9). In body folds, scraping and culture for Candida and examination of scalp and nails will distinguish inverse psoriasis from intertrigo and candidiasis (eFigure 6–18). Dystrophic changes in nails may mimic onychomycosis, and a potassium hydroxide (KOH) preparation or fungal culture is valuable in diagnosis (eFigure 6–19). The cutaneous features of reactive arthritis, pityriasis rosea, systemic lupus erythematosus, and syphilis mimic psoriasis.

There are many therapeutic options in psoriasis to be chosen according to the extent (body surface area [BSA] affected) and the presence of other findings (for example, arthritis). Systemic corticosteroids should never be used to treat flares of psoriasis because they may lead to severe rebound flares of the disease when they are tapered. Certain medications, such as beta-blockers, antimalarials, statins, and lithium, may flare or worsen psoriasis. Patients with moderate to severe psoriasis should be managed by or in conjunction with a dermatologist.

A. Limited Disease

For patients with large plaques and less than 10% of the BSA involved, the easiest regimen is to use a high-potency to ultra–high-potency topical corticosteroid cream or ointment. It is best to restrict the ultra–high-potency corticosteroids to 2–3 weeks of twice-daily use and then use them in a pulse fashion three or four times on weekends or switch to a mid-potency corticosteroid. Topical corticosteroids rarely induce a lasting remission. Additional measures are therefore commonly added to topical corticosteroid therapy. Calcipotriene ointment 0.005% or calcitriol ointment 0.003%, both vitamin D analogs, are used twice daily for plaque psoriasis. Initially, patients are treated with twice-daily topical corticosteroids plus a vitamin D analog twice daily. This rapidly clears the lesions; eventually, the topical corticosteroids are stopped, and once- or twice-daily application of the vitamin D analog is continued long-term. Calcipotriene usually cannot be applied to the groin or face because of irritation. Treatment of extensive psoriasis with vitamin D analogs may result in hypercalcemia, so that the maximum dose for calcipotriene is 100 g/week and for calcitriol it is 200 g/week. Calcipotriene is incompatible with many topical corticosteroids (but not halobetasol), so if used concurrently, it must be applied at a different time. Tar preparations, such as Fototar cream and LCD 10% in Nutraderm lotion, alone or mixed directly with triamcinolone 0.1%, are useful adjuncts when applied twice daily. Occlusion alone has been shown to clear isolated plaques in 30–40% of patients. Thin, occlusive hydrocolloid dressings are placed on the lesions and left undisturbed for as long as possible (a minimum of 5 days, up to 7 days) and then replaced. Responses may be seen within several weeks. For patients with numerous small plaques, phototherapy is the best therapy.

For thick plaques on the scalp, start with a tar shampoo, used daily if possible. Additional treatments include 6% salicylic acid gel (eg, Keralyt), P & S solution (phenol, mineral oil, and glycerin), or fluocinolone acetonide 0.01% in oil (Derma-Smoothe/FS) under a shower cap at night, and shampoo in the morning. In order of increasing potency, triamcinolone 0.1%, fluocinolone, betamethasone dipropionate, amcinonide, and clobetasol are available in solution form for use on the scalp twice daily. Tacrolimus ointment 0.1% or 0.03% or pimecrolimus cream 1% may be effective in intertriginous, genital, and facial psoriasis, since potent corticosteroids are not recommended due to skin atrophy.

B. Moderate Disease

Psoriasis affecting 10–30% of the patient’s BSA is frequently treated with UV phototherapy, either in a medical office or via a home light unit. Systemic agents listed below may also be used.

C. Generalized Disease

If psoriasis involves more than 30% of the body surface, it is difficult to treat with topical agents. The treatment of choice is outpatient narrowband UVB (NB-UVB) three times weekly. Clearing occurs in an average of 7 weeks, and maintenance may be required. Severe psoriasis unresponsive to outpatient ultraviolet light may be treated in a psoriasis day care center with the Goeckerman regimen, which involves use of crude coal tar for many hours and exposure to UVB light. Such treatment may offer the best chance for prolonged remissions.

Psoralen plus UVA (PUVA) photochemotherapy may be effective even in patients who have not responded to standard NB-UVB treatment. Long-term use of PUVA (greater than 250 doses) is associated with an increased risk of skin cancer (especially squamous cell carcinoma and perhaps melanoma) in persons with fair complexions. Thus, periodic examination (every 3–6 months) of the skin is imperative. Atypical lentigines are a common complication. There can be rapid aging of the skin in fair individuals. Cataracts have not been reported with proper use of protective glasses. PUVA may be used in combination with other therapy, such as acitretin or methotrexate.

Methotrexate is very effective for severe psoriasis in doses up to 25 mg once weekly according to published protocols. Long-term methotrexate use may be associated with cirrhosis. After receiving a 3.5–4-g cumulative dose, the patient should be referred to a hepatologist for evaluation. Administration of folic acid, 1–2 mg daily, can eliminate nausea caused by methotrexate without compromising efficacy.

Acitretin, a synthetic retinoid, is most effective for pustular psoriasis in oral dosages of 0.5–0.75 mg/kg/day. Liver enzymes and serum lipids must be checked periodically. Because acitretin is a teratogen and persists for 2–3 years in fat, women of childbearing age must wait at least 3 years after completing acitretin treatment before considering pregnancy. When used as single agents, retinoids will flatten psoriatic plaques, but will rarely result in complete clearing. Retinoids find their greatest use when combined with phototherapy—either UVB or PUVA, with which they are synergistic.

Cyclosporine dramatically improves psoriasis and may be used to control severe cases. Rapid relapse (rebound) frequently occurs after cessation of therapy, so another agent must be added if cyclosporine is stopped. The tumor necrosis factor (TNF) inhibitors etanercept (Enbrel), infliximab (Remicade), and adalimumab (Humira) are effective in pustular and chronic plaque psoriasis and are also effective for the associated arthritis. Infliximab provides the most rapid response and can be used for severe pustular or erythrodermic flares. Etanercept is used more frequently for long-term treatment at a dose of 50 mg subcutaneously twice weekly for 3 months, then 50 mg once weekly. All three TNF inhibitors can also induce or worsen psoriasis. IL-12/23 monoclonal antibodies (ustekinumab [Stelara], guselkumab), Janus kinase inhibitors (tofacitinib, approved for use in rheumatoid arthritis but with strong data supporting its use in psoriasis), and IL-17 monoclonal antibodies (secukinumab, brodalumab, and ixekizumab) may be the most effective treatments among biologics. The oral phosphodiesterase 4 inhibitor apremilast is an approved option for plaque-type psoriasis with minimal immunosuppressive effects and requires no laboratory monitoring. Given the large number of psoriasis treatments available, consultation with a dermatologist is recommended when considering systemic treatment for moderate to severe psoriasis.

The course tends to be chronic and unpredictable, and the disease may be refractory to treatment. Patients (especially those older than 40 years) should be monitored for metabolic syndrome, which correlates with the severity of their skin disease. Complications of systemic therapy occur and active monitoring for infection is needed.