2.3.1.4 Treatment
Topical therapy is generally recommended for small area of plaques，and moderate or severe psoriasis often requires phototherapy combined with systemic treatment.Phototherapy remains highly cost-effective for widespread psoriasis.Cyclosporin has a rapid onset of action，but is generally not suitable for continuous therapy.Methotrexate remains the most effective systemic agent.Biological agents can produce dramatic responses at the high cost.Rotating therapeutic agents with varying toxicities have conceptual appeal，and combination therapy may reduce toxicity and reduce the incidence of neutralizing antibodies to agents such as infliximab.
1.Topical treatment
（1）Corticosteroids：Topical application of corticosteroids in creams，ointments，lotions，foams，and sprays is the most frequent prescribed therapy for psoriasis.Low-to-mid strength creams are preferred in the intertriginous areas and on the face.To augment effectiveness of topical corticosteroids in areas with thick keratotic scale，the area should be hydrated by soaking prior to application，and covered with an occlusive dressing of a polyethylene film（Saran Wrap）or a sauna suit.Unfortunately，there is typically rapid recurrence of disease when corticosteroid therapy is discontinued.Side effects include epidermal atrophy，steroid acne，miliaria，and pyoderma.
（2）Tazaroten：Tazarotene is a nonisomerizable retinoic acid receptor specific retinoid.It appears to treat psoriasis by modulating keratinocytes differentiation and hyperproliferation，as well as by suppressing inflammation.
（3）Calcipotriene：Vitamin D3 affects keratinocytes differentiation partly through its regulation of epidermal responsiveness to calcium.Treatment with the vitamin D3 analog calcipotriene（Dovonex）in ointment，cream，or solution form has been shown to be very effective in the treatment of plaque-type and scalp psoriasis.Combination therapy with calcipotriene and high-potency steroids may provide greater response rates，fewer side effects，and steroid sparing.
（4）Macrolactams（calcineurin inhibitors）：Topical macrolactams such as tacrolimus and pimecrolimus are especially helpful for thin lesions in areas prone to atrophy or steroid acne.The burning commonly associated with these agents can be problematic，but may be avoided by prior treatment with a corticosteroid，and by application to dry skin，rather than after bathing.
（5）Salicyclic acid：Salicylic acid is used as a keratolytic agent in shampoos，creams and gels.It can promote the absorption of other topical agents.Widespread application of salicyclic acid may lead to salicylate toxicity manifesting with tinnitus，acute confusion，and refractory hypoglycemia，especially in patients with diabetes and those with compromised renal function.(https://www.daowen.com)
（6）Ultraviolet therapy：In most instances，sunlight can improve psoriasis.However，burning of the skin may cause Koebner's phenomenon and an aggravation.Artificial UVB is produced by fluorescent bulbs in broad-or narrow-band spectrums.Maximal effect is usually achieved at minimal erythemogenic doses（MED）.Maintenance UVB therapy after clearing contributes to the duration of remission and is justified for many patients.
（7）PUVA therapy：High-intensity longwave UV radiation（UVA）given 2 h after ingestion of 8-methoxypsoralen（Oxsoralen Ultra），twice a week，is highly effective，even in severe psoriasis.Most patients clear within 20-25 treatments，but maintenance treatment is needed.Although PUVA therapy is highly effective，in patients with less than 50％of the skin surface affected，UVB may be as good.PUVA therapy is a risk factor for skin cancer，including squamous cell carcinoma and melanoma.Men treated without genital protection are at an increased risk of developing squamous cell carcinomas of the penis and scrotum.Although the risk of cancer is dose related，there is no definitive threshold dose of cumulative PUVA exposure above which carcinogenicity can be predicted.
2.Systemic treatment
（1）Retinoids：Retinoids are suitable for the treatment of all types of psoriasis，such as etretinate administered orally in dosages of 0.75-1.0 mg/（kg·d）.However，retinoids have severe teratogenic effects，cause an increase in the levels of triglycerides，total cholesterolcan and liver enzymes.These side effects limit the application of retinoids in women of childbearing age，the elderly and children.Retinoids are contraindicated in pregnant patients.
（2）Immunosuppressants：Immunosuppressants are prescribed mostly for erythrodermic psoriasis，pustular psoriasis，and psoriasis arthropathica.The medication frequently used in this group is methotrexate given orally in a dosage of 10-25 mg/week for an adult patient，but the weekly dosage may not exceed 50 mg.Other choices include cyclosporine and tacrolimus.Methotrexate takes effect slowly，and the effect is usually obvious after 12 or 16 weeks treatment.Blood test，liver and kidney function should be tested regularly during the treatment.If the cumulative dose is more than 1500 mg，it is necessary to monitor liver fibrosis.Commonly recommended dose of cyclosporine is 3-5 mg/（kg·d），and should gradually reduce the dose after symptom control.Nephrotoxicity and hypertension should be monitored during long-term use.
（3）Biological agents：Several biological agents are available that can produce dramatic responses in some patients with psoriasis；while all are expensive.There are 3 classes of biological agents used to treat psoriasis：TNF inhibitors，IL-12/23 inhibitors，IL-17 inhibitors.Infliximab is a chimeric monoclonal antibody to TNF-α and requires intravenous infusion；etanercept is a fusion protein of human TNF-aⅡreceptor and the Fc region of IgG1；adalimumab is a recombinant fully human IgG1 monoclonal antibody to TNF-α.Alefacept is a fusion protein of the external domain of LFA-3 and the Fc region of IgG1，and blocks T-cell activation and triggers apoptosis of pathogenic T-cells.Etanercept provides a good balance of safety and efficacy.All biological agents used to treat psoriasis are administered subcutaneously except infliximab.Overall，there are no increased rates of serious infections or internal malignancies in patients with psoriasis who are treated using biological agents.Adverse effects that occur at slightly higher rates than placebo and are common to all biological agents include injection site reaction，nasopharyngitis，and upper respiratory tract infections.