Narrow-band UVB (NB-UVB) phototherapy at 311 nm is preferred over broadband UVB for which specific reason?
- A It penetrates deeper into the dermis, making it more effective for thick plaques
- B It delivers the therapeutic waveband (311 nm) while minimising erythemogenic and carcinogenic wavelengths (<300 nm) ✓
- C It eliminates the need for psoralen sensitization compared to PUVA
- D It has a shorter treatment course (fewer sessions) than broadband UVB
Correct answer: B. It delivers the therapeutic waveband (311 nm) while minimising erythemogenic and carcinogenic wavelengths (<300 nm)
Explanation
NB-UVB uses the therapeutic wavelength of 311–313 nm, which coincides with the action spectrum for psoriasis and vitiligo treatment, while excluding the more damaging shorter UVB wavelengths (<300 nm) that are responsible for erythema, DNA damage, and carcinogenesis. Option C is true but is a consequence/advantage of NB-UVB, not the primary reason it is preferred over BB-UVB (both are UVB and do not require psoralen). NB-UVB actually requires more sessions than PUVA but is preferred due to superior safety profile and no psoralen side effects.
Reference: Neena Khanna Illustrated Synopsis of Dermatology & STD, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.