When to use and avoid Narrowband Ultraviolet B (NBUVB) phototherapy in patients with moderate to severe psoriasis?

When to Use and Avoid Narrowband UVB Phototherapy in Psoriasis

Narrowband UVB (NB-UVB) phototherapy should be used as first-line phototherapy for moderate to severe plaque and guttate psoriasis, administered 2-3 times weekly, and is particularly appropriate when topical treatments have failed and before considering PUVA or systemic therapies. 1

Primary Indications for NB-UVB

NB-UVB is the preferred phototherapy modality for:

• Moderate to severe plaque psoriasis affecting >5-10% body surface area that has not responded adequately to topical treatments 1
• Guttate psoriasis, where NB-UVB shows particularly strong efficacy 1
• Thin plaque psoriasis, as thinner lesions respond better than thick plaques 2
• Pediatric psoriasis (ages 5-17 years) with moderate to severe disease, where it demonstrates 92% significant improvement rates 1
• Pregnancy, as NB-UVB has no known teratogenic effects and is considered first-line systemic therapy in pregnant patients 1

Clinical Situations Where NB-UVB Should Be Prioritized

NB-UVB should be chosen over PUVA when:

• Younger patients (age <20 years) require phototherapy, due to lower long-term carcinogenic risk 1, 2
• Fitzpatrick skin type I-II patients need treatment, as PUVA carries higher burn risk in fair-skinned individuals 2
• Patients are taking photosensitizing medications, which would complicate PUVA therapy 2
• Liver disease is present, as oral psoralen metabolism would be impaired 2
• Practical considerations favor simpler treatment, as NB-UVB requires no oral medication or protective eyewear between sessions 1

The British Association of Dermatologists guidelines explicitly state that PUVA should only be considered after NB-UVB has proven inadequately effective for chronic plaque psoriasis 1. This hierarchical approach reflects both efficacy data and safety considerations.

Treatment Protocol and Dosing

Standard NB-UVB administration:

• Frequency: 3-5 times weekly initially, can decrease to 2 times weekly upon improvement 1
• Initial dosing: Either 50% of minimal erythema dose (MED) or skin type-based (130-400 mJ/cm² depending on Fitzpatrick type I-VI) 1
• Dose escalation: Increase by 10% of initial MED for treatments 1-20, then as directed by physician 1
• Expected clearance: Typically requires 20-30 treatments for adequate response assessment 1
• Maintenance: After ≥95% clearance, taper to once weekly for 4 weeks, then once every 2 weeks, then once every 4 weeks at reduced doses 1

A critical pitfall: UVB machines must be metered weekly as lamps steadily lose power; failure to calibrate can result in underdosing despite higher numerical settings 1.

When NB-UVB Should NOT Be Used or Used with Caution

Relative contraindications and limitations:

• Very thick, extensive plaque psoriasis may respond inadequately to NB-UVB due to poor penetration; PUVA may be more appropriate as first-line phototherapy in these cases 1
• Scalp psoriasis shows limited improvement with NB-UVB, requiring adjunctive topical therapies 1
• History of melanoma or multiple non-melanoma skin cancers requires careful risk-benefit assessment, though long-term data show no significant association with skin cancer at median 5.5 years follow-up 1
• Inability to attend 2-3 times weekly for several months makes phototherapy impractical; home phototherapy may be considered as alternative 1
• Photosensitive conditions or lupus erythematosus are absolute contraindications 1

Darker-skinned individuals (Fitzpatrick IV-VI) with very thick lesions may benefit more from PUVA due to better UVA penetration, though NB-UVB remains first-line 1, 2.

Combination Therapy Considerations

NB-UVB can be safely combined with:

• Topical corticosteroids, calcipotriene, tazarotene, and emollients to enhance efficacy 1, 3
• Acitretin (particularly beneficial as it reduces plaque thickness and enhances NB-UVB penetration, though contraindicated in women of childbearing potential) 1, 3
• Biologic agents (etanercept, adalimumab, ustekinumab) when monotherapy is insufficient, with studies showing 95% PASI-75 response rates 4, 5

Exercise caution when combining with:

• Traditional systemic agents (methotrexate, cyclosporine, mycophenolate mofetil) - duration should be minimized and patients closely monitored due to cumulative immunosuppression and potential increased carcinogenic risk 1, 3

Special Populations

Pediatric patients: NB-UVB is recommended (Strength B) for moderate to severe pediatric plaque and guttate psoriasis, with 60% achieving ≥90% clearance at 12 weeks 1. Home phototherapy with appropriate education is viable for geographically isolated families 1.

Pregnant patients: NB-UVB is the preferred systemic approach, with no teratogenic effects documented 1. Genital shielding should be used routinely 1.

When to Escalate Beyond NB-UVB

Consider transitioning to PUVA or systemic therapy when:

• Inadequate response after 20-30 treatments (typically 8-12 weeks at 2-3 times weekly) 1
• Rapid relapse occurs despite maintenance therapy 1
• Patient cannot maintain treatment schedule required for efficacy 1
• Palmoplantar psoriasis is the primary manifestation, where PUVA shows superior efficacy 1

The British guidelines recommend PUVA should be offered before oral systemic therapy (Strength B) but considered before biologic therapy (Strength C) for chronic plaque psoriasis unresponsive to NB-UVB 1.

Practical Management Pearls

Face protection: Cover the face during treatment unless facial lesions are present, as facial skin responds to lower doses 1.

Genital shielding: Use routinely to prevent potential adverse effects 1.

Missed treatments: If 1-2 weeks missed, decrease dose by 25%; if 2-3 weeks missed, decrease by 50% or restart; if 3-4 weeks missed, restart protocol 1.

Realistic expectations: Many patients require once-weekly NB-UVB indefinitely for long-term maintenance rather than complete discontinuation 1. Additionally, clinical improvement (PASI reduction) does not consistently correlate with quality of life improvement, so patient-reported outcomes should be assessed independently 6.