What is the role of phototherapy in the treatment of plaque psoriasis?

Updated: Mar 17, 2021
  • Author: Harvey Lui, MD, FRCPC; Chief Editor: Dirk M Elston, MD  more...
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Initiate phototherapy only in the presence of extensive and widespread disease (generally practically defined as more lesions than can be easily counted). Resistance to topical treatment is another indication for phototherapy.

The 2 main forms of phototherapy are ultraviolet B (UVB) irradiation and psoralen plus ultraviolet A irradiation (PUVA). Proper facilities are required for both UVB irradiation and PUVA photochemotherapy.

UVB irradiation uses light with wavelengths of 290-320 nm (in comparison, the visible light range is 400-700 nm). Narrow-band UVB phototherapy uses a fluorescent bulb with a narrow emission spectrum that peaks at 311 nm. This selective and relatively longer wavelength is more effective than broadband UVB for the treatment of plaque-type psoriasis, and poses less risk of burning. [16] Excimer laser UVB therapy can deliver high-dose light to limited plaques.

UVB therapy is usually combined with one or more topical treatments. The Goeckerman regimen uses coal tar followed by UVB exposure and has been shown to induce disease remission in more than 80% of patients. The Ingram method comprises anthralin application following a tar bath and UVB treatment. At present, UVB is more commonly combined with topical corticosteroids, calcipotriene, tazarotene, or simply bland emollients. Etanercept and narrow-band UVB combination therapy reportedly was successful. [17]

UVB phototherapy is extremely effective for treating moderate-to-severe plaque psoriasis. The major drawback of this therapy is the time commitment required for treatments and the accessibility of the UVB equipment. Patients may dislike the unpleasant odor when coal tar is added.

Home ultraviolet therapy can overcome some of the logistical problems associated with phototherapy. Because of the expense of the home units, it is most suitable for patients who require long-term maintenance therapy.

PUVA photochemotherapy, also known as PUVA, uses the photosensitizing drug methoxsalen (8-methoxypsoralen) in combination with UVA irradiation to treat patients with more extensive disease. UVA irradiation uses light with wavelengths of 320-400 nm. PUVA interferes with DNA synthesis, decreases cellular proliferation, and induces apoptosis of cutaneous lymphocytes, leading to a localized immunosuppression.

More than 85% of patients report relief of disease symptoms with 20-30 treatments. Therapy is usually administered 2-3 times per week in an outpatient setting, with maintenance treatments every 2-4 weeks until remission.

Adverse effects of PUVA therapy include nausea, pruritus, and a burning sensation. Long-term complications include increased risks of photo damage to the skin and (more importantly) skin cancer. PUVA has been combined with oral retinoid derivatives to decrease the cumulative dose of UVA radiation to the skin.

Also see Clinical Practice Guidelines.

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