photochemotherapy

Photochemotherapy is a medical treatment that combines a photosensitizing agent with exposure to ultraviolet light to achieve therapeutic effects. It is most often used for skin diseases and certain immune-mediated conditions. The best-known form is psoralen plus ultraviolet A (PUVA), in which a patient receives psoralen either orally or topically and is then irradiated with UVA light. Bath PUVA uses psoralen dissolved in a bath, and topical PUVA applies the photosensitizer directly to the skin. Extracorporeal photopheresis (ECP) is a related modality in which blood is treated with a photosensitizer and UVA light outside the body and then reinfused; this approach is used for some cases of cutaneous T-cell lymphoma and graft-versus-host disease.

The mechanism involves psoralen intercalating into DNA; upon UVA exposure, it forms cross-links that inhibit DNA replication and promote apoptosis in rapidly proliferating skin cells. In addition, photochemotherapy has immunomodulatory effects, altering T-cell function and cytokine signaling, which can reduce inflammatory activity in selected dermatologic and immunologic conditions.

Indications include plaque psoriasis, certain forms of eczema, and cutaneous T-cell lymphomas such as mycosis fungoides and Sézary syndrome. It may be employed in other photodermatoses or refractory skin conditions when conventional therapies are insufficient. ECP is specifically indicated for conditions like CTCL and graft-versus-host disease.

Risks and safety considerations include acute sunburn or phototoxic reactions during treatment, as well as long-term risks from cumulative UVA exposure, such as photoaging and an increased risk of skin cancers. Protective eyewear and skin monitoring are important. Treatment requires specialized facilities and careful dosing, with planning to balance efficacy against cumulative UV exposure.