What is the role of phototherapy in treating psoriasis?

How Phototherapy Works in Treating Psoriasis

Narrowband UVB phototherapy is a safe and effective treatment for psoriasis that works by interfering with DNA synthesis, decreasing keratinocyte proliferation, and modulating immune responses in the skin. 1

Mechanisms of Action

Phototherapy treats psoriasis through several mechanisms:

• Inhibits keratinocyte hyperproliferation by interfering with DNA synthesis and cellular turnover 1
• Creates pyrimidine dimers, causes membrane lipid peroxidation, and induces transcriptional factors in skin cells 1
• Decreases the number of Langerhans cells, inhibiting antigen presentation by damaging cell membranes and reducing expression of cell surface molecules 1
• Alters cytokine secretion in macrophages and down-regulates Th17 cells, which play a central role in psoriasis pathogenesis 1
• Suppresses local immune responses, causing a shift from T-helper 1 (Th1) to T-helper 2 (Th2) phenotype 2
• Inhibits angiogenesis, which contributes to psoriatic plaque formation 1

Types of Phototherapy for Psoriasis

Narrowband UVB (NB-UVB)

• Most commonly used and preferred form of phototherapy with wavelength of 311-313 nm 1
• More effective than broadband UVB with superior efficacy and safety profile 1
• Recommended as first-line treatment for extensive plaque-type psoriasis 3
• Typically administered 2-3 times weekly for at least 3 months 3
• Achieves clearance in 50-92% of patients with minimal adverse effects 1

Broadband UVB (BB-UVB)

• Traditional form of UVB therapy used for over 75 years 4
• Less effective than narrowband UVB in comparative studies 1
• Studies show 60% of patients have equal results with BB-UVB vs. NB-UVB, but 40% have superior results with NB-UVB 1

PUVA (Psoralen plus UVA)

• Combines UVA light with psoralen (a photosensitizing medication) 1
• More effective for refractory psoriasis plaques than UVB but has greater side effects 5
• Limited supporting evidence for use in children 1
• Associated with increased risk of keratinocytic cancers after >200 treatment sessions 2

Excimer Laser

• Targeted phototherapy for localized psoriatic lesions 1, 5
• Particularly effective for nail psoriasis compared to other laser treatments 5
• May be efficacious but has limited supporting evidence in children 1

Clinical Efficacy

• NB-UVB leads to histopathological resolution of psoriasis lesions in 88% of cases (compared to 59% with BB-UVB) 1
• Maintenance therapy with NB-UVB (twice weekly for 4 weeks followed by once weekly for 4 weeks) keeps 55% of patients in remission at 1 year, compared to 33% without maintenance 1
• In pediatric patients, NB-UVB achieves 90% skin clearance in 60% of patients after 12 weeks of twice-weekly treatment 1
• Combination therapy with topical agents (emollients, vitamin D analogs) enhances efficacy 4

Practical Considerations

• Typical treatment regimen involves 2-3 sessions per week for at least 3 months 3
• Onset of efficacy often delayed (>4 weeks), which can lead to frustration and non-adherence 1
• Home phototherapy equipment is a viable alternative for geographically isolated patients 1
• Natural sunlight in moderation may be recommended when in-office phototherapy is not feasible 1

Common Pitfalls and Caveats

• Proper eye protection (goggles) is essential during treatment 1
• Male patients should use genital shields during treatment 1
• Regular monitoring by trained personnel is necessary for optimal results 1
• Patients with multiple risk factors for melanoma, multiple non-melanoma skin cancers, or immunosuppression require careful screening before initiating phototherapy 1
• Monthly examinations by a dermatologist are recommended during treatment 1
• Vitamin D analogs should be applied after phototherapy to avoid inactivation 6

Patient Selection

• Best suited for moderate to severe plaque and guttate psoriasis 1
• Excellent option for patients with extensive disease where topical therapy is impractical 4
• Appropriate for patients with medical problems that preclude systemic medications 4
• Consider patient's employment schedule, commitment, flexibility, location of phototherapy unit, and transportation when recommending phototherapy 4

Phototherapy remains one of the safest and most effective treatment strategies for psoriasis, with a superior systemic safety profile compared to systemic or biologic agents for patients with generalized disease 4, 3.