Principles of Phototherapy
Phototherapy or ‘light therapy’ has been used to treat skin diseases since ancient times. Modern phototherapy uses specific wavelengths typically within the ultraviolet part of the electromagnetic spectrum, by means of treatment modalities including UVB phototherapy (narrow‐band UVB 311–313 nm), photochemotherapy (psoralen and UVA; PUVA), UVA‐1 phototherapy and extracorporeal photochemotherapy (photopheresis) to treat a variety of skin diseases. The most frequently treated skin diseases include psoriasis, eczema, cutaneous T‐cell lymphoma (CTCL; mycosis fungoides), vitiligo and various photodermatoses. Narrow‐band UVB is the most commonly used phototherapy and is the phototherapy of first choice for most indications. PUVA is used mainly for UVB phototherapy treatment failures and in specific conditions, such as palmoplantar pustulosis, pustular psoriasis and pityriasis rubra pilaris. UVA‐1 is particularly useful for the treatment of sclerotic skin conditions such as morphoea and for atopic eczema. Photopheresis is indicated for the severe forms of CTCL: Sézary syndrome and graft‐versus‐host disease. The main short‐term hazard of UV therapy is burning of the skin and the primary long‐term concern is of skin cancer risk. Systemic PUVA is associated with a dose‐related increased risk of squamous cell carcinoma. No evidence of increased risk of skin cancer has yet been shown for UVB or UVA‐1 phototherapy. To avoid adverse events, careful patient selection, education and assessment of skin cancer risk is important. In addition, accurate dosimetry and UV lamp maintenance is required. Patient and staff safety is of paramount importance and is ensured by the establishment of good clinical governance pathways.
Keywords narrow‐band UVB phototherapy, photochemotherapy, psoralen and UVA, PUVA, UVA‐1 phototherapy, extracorporeal photochemotherapy (photopheresis), adverse events, burning, skin cancer, patient selection, patient/staff safety, clinical governance