Jack of all trades: Abolishing acne is among PDT's many uses

Washington - The therapeutic uses of photodynamic therapy (PDT) are steadily growing today, and its use is indicated in an ever-widening range of conditions in dermatology, from skin cancer and actinic keratoses to more recent applications in cosmetic dermatology such as the treatment of acne and rosacea and for photorejuvenation.

One expert in the field discussed the uses of PDT and its successes in cosmetic conditions, speaking at the 65^th Annual Meeting of the American Academy of Dermatology, here.

Evolution of acne treatment

"With annual costs of over-the-counter (OTC) and prescription medications estimated to be in the tens of billions of dollars each year, as well as the well-known possible adverse events of isotretinoin and long-term antibiotic therapy, patients and physicians alike are looking to new alternatives of acne therapy, now," says Bruce E. Katz, M.D., clinical professor at New York's Mount Sinai School of Medicine and director at the Juva Skin & Laser Center and of the Cosmetic Surgery & Laser Clinic at Mount Sinai Hospital, New York.

Dr. Katz says the use of laser for acne evolved from the use of nonablative lasers for wrinkles and scars. There was a significant thermal effect seen in terms of dermal remodeling of the sebaceous glands, and this positive effect was then further applied therapeutically in acne vulgaris.

The light sources effective in PDT include pulsed dye lasers, intense pulsed light (IPL), blue light and LED light sources. Dr. Katz explains that a PDT procedure involves the application of ALA - the topical photosensitizer. A small molecule, ALA is ideal for applying topically, while avoiding systemic side effects. P. acnes converts ALA to protoporphyrin-9, which then absorbs laser energy and destroys the bacteria, clearing acne lesions.

Dr. Katz says that a "blue light" therapy for acne vulgaris can consist of clear light source (similar to other IPLs) with a 405 to 420 nm wavelength and a fluence range of 200 to 500 mW/cm, or a Blu-U light source with a 417 nm wavelength and a fluence range of 100 to 300 mW/cm.

"One of the keys to a successful blue light therapy in acne is a repetitive exposure. The photoexcitation of bacterial porphyrins stimulates and destroys surface bacteria, very similar to the therapeutic effects of benzoyl peroxide," Dr. Katz tells Dermatology Times.

Recent trials show "green light" therapy achieving up to a 30 percent to 40 percent reduction in acne severity. For optimal results, Dr. Katz suggests multiple and repetitive sessions - approximately two visits per week for six weeks. According to Dr. Katz, the disadvantages seen with green light therapy are that its penetration is limited to the surface bacteria, yielding only a temporary effect. Unfortunately, if the therapy is stopped, P. acnes will recolonize.

Fire and ice

Dr. Katz cites a study in which the combination therapy of a 1,450 nm diode laser and cryotherapy was compared to cryotherapy alone to treat acne on the backs of 27 patients.

Results showed a 63 percent reduction in lesion counts after a single treatment, and a 98 percent reduction in acne lesions at 24 week follow-up in patients treated with combination therapy. There were no hyper-or hypopigmented lesions reported.

"Though the mechanism of action is not completely understood, the thermal injury to the sebaceous glands is obvious. The 1,450 nm diode laser penetrates to the ideal depth in the sebaceous gland and produces a very positive therapeutic effect," Dr. Katz says.

LED photomodulation uses a low-intensity light therapy (590 nm yellow light) to nonthermally modulate the activity of cells. Dr. Katz says that this type of light source therapy is effective for all skin types and has no adverse effects. A major advantage here is that physicians can treat large areas (e.g., chest and back) in one visit.