The phototoxicity of photodynamic therapy may be suppressed or enhanced by modulation of the cutaneous vasculature

In photodynamic therapy, the threshold for light induced toxicity depends on the drug concentration and the light dose. This study was aimed to show for vascular photosensitizers that the toxicity threshold on normal tissue may be predictably modified by modulation of the cutaneous vasculature. Albino rabbits were injected with 1.0 mg/kg of a vascular photosensitizer, benzoporphyrin derivative monoacid ring-A. The threshold light dose for toxicity to normal skin was determined at an absorption maximum of the drug (694 nm), 1 h after drug injection. The cutaneous vasculature was dilated by prior skin exposure to ultraviolet radiation or was constricted by iontophoretic application of epinephrine. Threshold toxicity was determined clinically and by assessing the effective concentration of hemoglobin in the skin by diffuse reflectance spectroscopy (DRS). Tissue samples that received threshold doses were investigated with light and electron microscopy. The toxicity threshold increased by 3.2+/-0.9 (mean+/-S.D.) following vasoconstriction and decreased by 3.6+/-0.8 following vasodilation, compared to control sites. Light and electron microscopy showed similar findings at threshold for both vasodilated and vasoconstricted sites. Therefore vascular modulation may be used to predictably enhance or suppress the level of phototoxicity of normal skin.

Skin necrosis due to photodynamic action of benzoporphyrin depends on circulating rather than tissue drug levels: implications for control of photodynamic therapy

In an ideal world, photodynamic therapy (PDT) of abnormal tissue would reliably spare the surrounding normal tissue. Normal tissue responses set the limits for light and drug dosimetry. The threshold fluence for necrosis (TFN) was measured in normal skin following intravenous infusion with a photosensitizer, benzoporphyrin derivative monoacid ring A (BPD-MA) Verteporin as a function of drug dose (0.25-2.0 mg/kg), wavelength of irradiation (458 and 690 nm) and time interval (0-5 h) between drug administration and irradiation. The BPD-MA levels were measured in plasma and skin tissue to elucidate the relationship between TFN, drug kinetics and biodistribution. The PDT response of normal skin was highly reproducible. The TFN for 458 and 690 nm wavelengths was nearly identical and the estimated quantum efficiency for skin response was equal at these two wavelengths. Skin phototoxicity, quantified in terms of 1/TFN, closely correlated with the plasma pharmacokinetics rather than the tissue pharmacokinetics and was quadratically dependent on the plasma drug concentration regardless of the administered drug dose or time interval between drug and light exposure. This study strongly suggests that noninvasive measurements of the circulating drug level at the time of light treatment will be important for setting optimal light dosimetry for PDT with liposomal BPD-MA, a vascular photosensitizer.

Treatment of small nevomelanocytic nevi with a Q-switched ruby laser

BACKGROUND

Small nevomelanocytic nevi are common and some are of cosmetic concern. Conventional therapy may cause a scar or permanent hypopigmentation.

OBJECTIVE

Our purpose was to determine whether selective photothermolysis of pigmented cells by Q-switched ruby laser treatment removes small nevomelanocytic nevi in a nonscarring fashion.

METHODS

Twelve patients with 18 small nevomelanocytic nevi were treated with a Q-switched ruby laser (694 nm, 28 nsec) at fluences of 8 J/cm2. Biopsy specimens were obtained after treatment at varying time intervals.

RESULTS

Twelve lesions (67%) showed a complete response and six lesions (33%) had a partial response. The only adverse sequela observed was mild fibrosis of the papillary dermis, without loss of papillary architecture.

CONCLUSION

The Q-switched ruby laser is effective in removing small melanocytic nevi. However, some might recur depending on the depth of the nevomelanocytic nests.

Treatment of nevus spilus with the Q-switched ruby laser

BACKGROUND

Q-switched lasers have shown to be effective in the removal of unwanted cutaneous pigmentation. Benign cutaneous pigmented lesions represent a heterogeneous group. Nevus spilus is a relatively uncommon pigmented lesion characterized by dark, hyperpigmented dots scattered over a tan-colored macule.

OBJECTIVE

A cohort of patients with nevus spilus was studied to determine the effects of Q-switched ruby and Q-switched Nd:YAG laser treatment on clearance of pigment and to evaluate potential side effects.

METHODS

Six patients with nevus spilus were treated with the Q-switched ruby laser (QSR). In addition, three lesions received a test treatment with the Q-switched Nd:YAG (QSYAG) laser at 532 or 1064 nm. The results of treatment were documented during follow up visits.

RESULTS

Most lesions showed a near-complete or complete response to laser treatment. In one case partial hyperpigmentation occurred after treatment and in one case no follow-up could be obtained. In the three cases that received both QSR and QSYAG laser treatment, the QSR laser was shown to be the most effective in removing pigment.

CONCLUSION

Nevus spilus can be treated effectively with the Q-switched ruby laser.

Treatment of pyogenic granulomas with the 585 nm pulsed dye laser

BACKGROUND

Current therapeutic alternatives for pyogenic granulomas include surgical excision, electrodesiccation and curettage, cryotherapy, and ablation with CO2 or continuous-wave vascular lasers.

OBJECTIVE

Our purpose was to investigate the use of the 585 nm flashlamp-pumped pulsed dye laser (585 nm PDL) for the treatment of pyogenic granulomas in terms of efficacy, advantages in technique, and side effects.

METHODS

Eighteen patients with symptomatic pyogenic granulomas in a variety of locations were treated with the 585 nm PDL and examined.

RESULTS

Sixteen of 18 treated patients demonstrated both symptomatic and clinical clearing of the lesions with excellent cosmetic results after treatment. The two patients who dropped out after one to two 585 nm PDL treatments were eventually treated successfully with electrodesiccation and curettage. No postoperative complications and no persistent pigmentary changes or scarring were observed. The procedure required no anesthesia, and postoperative care was limited to the application of a topical antibiotic ointment.

CONCLUSION

Our experience suggests that treatment of pyogenic granulomas with the 585 nm PDL is a safe, effective, and reasonable alternative to conventional therapy.