phototherapy

phototherapy
Name	Phototherapy
Synonyms	Light therapy
Specialty	Dermatology, Neonatology, Psychiatry
MeshID	D010782
MedlinePlus	001466

phototherapy is a therapeutic medical intervention that utilizes specific wavelengths of electromagnetic radiation, primarily within the visible spectrum and ultraviolet range, to treat various conditions. It is a cornerstone treatment in several medical fields, including dermatology for skin disorders and neonatology for newborn jaundice. The therapeutic effect is achieved through precise biochemical interactions initiated when photons of light are absorbed by target molecules in the skin, blood, or brain.

Mechanism of action

The biological mechanism depends heavily on the wavelength employed and the target chromophore. For neonatal hyperbilirubinemia, blue light around 450 nm is absorbed by bilirubin molecules in the capillaries of the skin, converting them into water-soluble isomers that can be excreted without requiring conjugation in the liver. In dermatological applications, particularly for psoriasis and vitiligo, ultraviolet B radiation is absorbed by DNA and urocanic acid in keratinocytes, leading to immunosuppression and reduced proliferation of skin cells. The action of narrowband UVB involves modulating the activity of T cells and altering cytokine profiles. For mood disorders like seasonal affective disorder, bright light therapy is thought to suppress nocturnal secretion of melatonin from the pineal gland and influence serotonin pathways and circadian rhythms in the suprachiasmatic nucleus.

Types of phototherapy

Major classifications are defined by the light source and spectral output. Broadband UVB therapy uses a wider range of ultraviolet wavelengths, while narrowband UVB, centered at 311 nm, has become a standard due to greater efficacy and a better safety profile. Psoralen plus UVA combines oral or topical psoralen with exposure to ultraviolet A radiation. Blue light therapy is primarily used for neonatal jaundice and certain acne treatments, whereas red light and LED therapy are explored for wound healing and cosmetic applications. Excimer laser delivers a focused beam of 308 nm UVB for targeted treatment of small plaques. For psychiatric conditions, bright light therapy devices typically emit intense white light at 10,000 lux.

Medical applications

Its primary and most established use is in neonatology for treating unconjugated hyperbilirubinemia to prevent kernicterus. In dermatology, it is a first-line treatment for moderate-to-severe psoriasis, eczema, vitiligo, cutaneous T-cell lymphoma, and pruritus. Within psychiatry and neurology, it is a recommended treatment for seasonal affective disorder and is used for non-seasonal depression, sleep disorders such as delayed sleep phase syndrome, and dementia-related agitation. Other applications include treating acne vulgaris with blue or red light, managing graft-versus-host disease, and adjunctive use in certain cases of mycosis fungoides.

Side effects and risks

Acute side effects are common and typically mild, including erythema, pruritus, and xerosis resembling a sunburn. Overexposure can lead to painful blistering. Long-term risks are primarily associated with cumulative UV exposure, significantly increasing the likelihood of photoaging, actinic keratoses, and both non-melanoma skin cancer and melanoma. PUVA therapy carries an elevated risk of squamous cell carcinoma. Ocular exposure without proper protection can cause photokeratitis or contribute to cataract formation. Special considerations exist for neonates, where potential risks include dehydration, temperature instability, and retinopathy if eye protection is inadequate.

History and development

The therapeutic use of sunlight, or heliotherapy, was practiced in ancient cultures, including those of Egypt and Greece. Modern phototherapy began in the late 19th century when Niels Ryberg Finsen of Denmark successfully used concentrated light radiation to treat lupus vulgaris, for which he received the Nobel Prize in Physiology or Medicine in 1903. The seminal discovery for neonatal treatment occurred in the 1950s at Rochford General Hospital in Essex, when nurse Sister J. Ward and Dr. R. J. Cremer observed that sunlight reduced jaundice, leading to the development of the first phototherapy systems. The introduction of narrowband UVB in the 1980s, pioneered by institutions like the Massachusetts General Hospital, revolutionized dermatological treatment.

Equipment and administration

Standard equipment includes fluorescent lamp banks, light-emitting diode panels, and excimer laser systems. For whole-body treatment, patients stand in a vertical cabinet lined with UVB or UVA lamps, or lie under a horizontal canopy. Targeted delivery systems, like the Excimer laser, allow for precise treatment of individual lesions. Dosimetry is critical and is typically based on the patient's minimal erythema dose or standardized protocols. Administration for neonates involves placing the unclothed infant under a bank of blue lights or on a fiberoptic phototherapy blanket, with the eyes shielded by protective patches. Treatment schedules vary from brief, daily sessions for SAD to several weekly exposures in a dermatology clinic over many weeks.

Category:Medical treatments Category:Dermatology Category:Neonatology