Treating Solar Lentigines:
Traditional treatments at a glance — plus, a look at a cutting-edge option.

S olar lentigines, though usually benign pigmented lesions, are a major concern for many patients because they’re typically found on sun-exposed areas such as the face, arms and hands, making them aesthetically undesirable. These lesions can vary in size and may increase in number with age. A variety of treatment modalities have been used over the years to remove solar lentigines, including cryotherapy, trichloroacetic acid, topical tretinoin and bleaching agents such as hydroquinone. More recently, laser surgery has emerged as a novel and efficacious therapeutic modality. Over the past several years, a plethora of studies have been published supporting the use of laser surgery to treat solar lentigines. Additionally, various studies have evaluated and compared the efficacy of these different treatment options. Here, I’ll review the treatments available. A look at Treatments Liquid nitrogen has been used to treat lentigines with great success for many years. Liquid nitrogen is easily accessible, relatively inexpensive and very easy to use. Destruction of melanocytes occurs at temperatures of -4 to -7 degrees C, while squamous cells resist injury even at -20 degrees C. Patients endure mild to moderate discomfort during treatments, and adverse events are usually unremarkable. However dermal damage can occur when too much treatment is given. At temperatures less than -20 degrees C, scars and hypopigmentation can occur. These events can be easily avoided with attention to proper technique making results highly operator dependent. Large areas can be easily treated in one session and healing time after treatments is short.1 Trichloroacetic acid ( TCA ) has been used for chemical peeling since 1926. It works by precipitating protein, causing necrosis and sloughs both the actinically damaged and normal skin cells, followed by replacement with new epidermis and connective tissue. The penetration of TCA is dependent on several factors. Application technique, skin thickness, concentration of TCA, prior use of retinoic or glycolic acid and prepeel preparation are a few factors that can influence the penetration of TCA and hence the outcome of treatment. The most commonly used concentration for the treatment of lentigines is probably 35% TCA. The acid can be applied with or without abrasion, and should result in a frosted white appearance with mild surrounding erythema. For several days following application, crust may appear which then sloughs off resulting in a pink-red patch that gradually fades and returns to normal colored skin.2 Retinoic acid has been shown to lighten lentigines, and has also been used successfully in combination with acid peels and bleaching agents, such as hydroquinone. Few data are available to evaluate to the efficacy of hydroquinone in treating lentigines. Other lightening agents include 4-hydroxyanisole (4HA or Mequinol), which is a tyrosinase inhibitor available in Europe and is less irritating than hydroquinone. It’s been used in combination with tretinoin and reported to be well tolerated with minimal side effects of burning, stinging and desquamation. A study by Fleisher et al in March 2000 evaluated the efficacy and safety of the combination product of 2% 4HA/0.01% tretinoin solution (Solage) in two Phase III, randomized, controlled, double-blind studies. The 4HA/tretinoin combination was clinically superior to each of its active components and to the vehicle in the treatment of solar lentigines.3 Recent mainstay of treatment Lasers have become the mainstay of treatment for lentigines in recent years, despite the high cost to both patients and physicians. Over the past 20 years, the development of short pulsed pigment-specific lasers has enabled physicians to treat a diverse spectrum of pigmented lesions with good tissue selectivity and minimal post-operative complications. The theory of selective photothermolysis, first proposed by Anderson and Parish in 1983, has allowed physicians to use lasers to target specific structures in the skin without damaging the surrounding tissue. In order for a laser to achieve this effect, several requirements must be met: - First the laser must emit at a wavelength, which is highly absorbed by that structure. -Second, sufficiently high energies must be produced in order to inflict thermal damage to the target. - Finally, the time of tissue exposure to the laser should be short enough to limit the damage to the target without heat diffusion to the surrounding tissue.4 When treating cutaneous pigmentation with lasers, you must consider distribution of the pigment in the skin, the location of the pigment in the skin and the absorption characteristics of the pigment. Melanin is the target chromophore when treating solar lentigines. In order to be effective and avoid unwanted adverse effects, use a wavelength that avoids absorption by other skin chromophores. When targeting melanin, the desired wavelengths lie between 630 nm and 1100 nm. Pulse width also plays a role. The pulse duration of the laser should be shorter than the thermal relaxation time of melanin. Melanosomes require nanosecond pulse durations for their selective disruption. Cutaneous lasers traditionally used for the treatment of solar lentigines include the frequency-doubled, Q-switched Nd:YAG 532 nm laser, Q-switched ruby laser, the 510 nm pigmented lesion dye laser and the 532 nm emitting diode laser. Several recent studies have compared the efficacy of various lasers with the aforementioned peeling agents as well as with liquid nitrogen treatments.4,5 What the Studies Revealed A study by Li and Yang recently compared the frequency doubled Q-switched Nd:YAG (532 nm) laser and 35% TCA for the treatment of face lentigines. Twenty patients with a total of 37 lentigines were randomly collected. Each lentigo was divided into medial and lateral halves. The medial half was treated with the laser and the lateral half treated with 35% TCA. The efficacy after one treatment was compared after 6 months. The results showed that the frequency doubled Q-switched Nd:YAG laser (532 nm) had a better result than that of the 35% TCA. There are some issues to consider, though. The sample size of this study was small, the difference in improvement scores was small, and 21% of those lentigines treated had the same improvement by laser and TCA. Additionally, the study population was restricted to patients with Fitzpatrick skin types III and IV, making the study valid for this population only.2 More recently, Todd et al reported a comparison of three lasers and liquid nitrogen for treating solar lentigines. A randomized, controlled comparative study with blinded observers was performed, including 27 patients with multiple solar lentigines on the dorsum of the hands. The treatments for this study included liquid nitrogen, the Medlite II frequency-doubled Q-switched Nd:YAG laser (Continuum Biomedical, Livermore, CA), The HGM K1 krypton laser (HGM Medical Laser Systems Inc., Salt Lake City, Utah) and the Diolite 532 nm diode pumped laser (Iridex Corp., Mountain View, CA). Photographs were taken prior to treatment and then again 6 and 12 weeks after treatment, and evaluated by blinded observers. The results showed that the frequency-doubled Q-switched Nd:YAG laser was most likely to provide significant lightening, followed by the HGM K1 krypton laser, the 532 nm diode and liquid nitrogen. Additionally, the frequency-doubled Q-switched Nd:YAG laser had the fewest adverse events, while the krypton laser had the most. Of the 27 patients participating, 25 preferred laser therapy over cryotherapy, with the frequency-doubled Q-switched Nd:YAG laser being the most preferred. Although liquid nitrogen didn’t provide the most desirable results, it wasn’t as likely to result in unwanted adverse events as much as the krypton and diode lasers did. Liquid nitrogen is also significantly less expensive and more accessible than lasers. This study evaluated only one-time treatments. It’s still possible that repeated treatments with liquid nitrogen could provide improved results with minimal adverse events.6 In the July 2002 issue of Dermatologic Surgery, Kawada et al., described clinical improvement of solar lentigines and ephelides with an intense pulsed light (IPL) source. This broad-band visible light emitted from a noncoherent, nonlaser, filtered flashlamp, emitting a range of 500 to 1200 nm has been used to treat a variety of skin lesions, including rhytides, wrinkling, skin coarseness, telangiectasias, unwanted hair and pigmented lesions. Sixty patients with facial pigmentary lesions completed 3 to 5 treatments with the IPL. Of the 60 participants, 48% had more than 50% improvement and 20% had more than 75% improvement, supporting that IPL may be a new treatment modality for the removal of solar lentigines. Adverse events included “microcrusts” which disappeared within 2 weeks, and mild burning and pain.7 Many Choices In summary, we have a variety of treatment options to choose from for treating lentigines. Although new technology offers promise, more study is needed to support their use. Adverse events, as well as the high cost of some of the laser systems, may restrict their regular use. To date, however, most studies support the superiority of laser technology in the efficacious treatment of solar lentigines. Furthermore, the possibility of multiple uses for one laser system may offer cost benefits for you and your patients.