Dermatosis papulosa nigra (DPN) is a chronic benign cutaneous condition that is common mainly among African American patients, and also occurs among dark-skinned Asians, Hispanics, and Polynesians, but the exact frequency is unknown 1. The condition affects about 35% of American blacks, whereas there is a lower frequency in African Americans with a fairer complexion. Females are more frequently affected than males. It usually commences in adolescence. The pathophysiology of DPN is not known. The occasional positive family history may suggest a genetic propensity.
It is typically distinguished by multiple, small, 1–5 mm diameter, smooth, firm, black or dark-brown papules on the malar region of the face and neck, and is also found on the upper back and the chest. The incidence, number, and size of the lesions increase with age 2,3.
Many patients find these lesions unpleasant and consult physicians to discuss options for removal.
Locally destructive treatments such as curettage, freezing with liquid nitrogen (cryotherapy), and electrodesiccation, followed by curettage have been complicated by pigmentary alterations (hyperpigmentation or hypopigmentation), scarring, and keloid formation 4,5.
This study was carried out to evaluate the long-term efficacy and safety of a long-pulsed Nd-YAG laser for the treatment of DPN in dark skin.
Patients and methods
Sixty patients with multiple papular lesions of DPN were enrolled in this study over an 18-month period between January 2012 and June 2013 in Cairo, Egypt, and Khartoum, Sudan. Inclusion criteria included no previous treatment of the lesions, whereas exclusion criteria included being on systemic medications that are known to increase photosensitivity, oral or topical retinoid within 1 year before initiation of the study, tendency for keloid or hypertrophic scar formation, and pregnancy. All patients provided informed consent following the Helsinki declaration.
The treatment protocol consisted of two laser sessions 3 weeks apart using a long-pulsed Nd-YAG laser (1064 nm) with a 20 ms pulse duration and a fluence range between 100 and 120 J/cm2, using a 3 or a 5 mm spot size, according to the size of the treated lesions, applying two stacking pulses. Skin air cooling accompanied laser pulses. After each treatment session, patients were instructed to apply a topical antibiotic cream twice daily for 5 days as a prophylactic measure to prevent secondary infection and to use a sunscreen with an SPF of 50+.
Photographs of the targeted treatment areas of each patient were taken at baseline and 3 months after the second treatment session as well as 12 months after the last session. Standardized photography was performed using the same digital camera (Nikon D300s; Nikon Imaging, Tokyo, Japan) and the same settings used to acquire all photographs.
Blinded assessments were performed by three independent physicians using before and after photographs (unlabelled) that were not arranged in chronological order. Reviewers were asked to identify the before and after photographs and evaluate the degree of improvement using a five-point scale at the 12th-month follow-up by calculating the mean score of the three reviewers. They also commented on the adverse effects, if any, such as textural changes, scarring, or pigmentary changes. In the evaluation of treatment response, complete clearance was defined as complete absence of clinically apparent papular lesions without any pigmentary or textural changes. Marked improvement was defined as a greater than 75% reduction in the papular lesions size and number. Moderate improvement was defined as a greater than 50–75% reduction in papular size or number. Mild improvement was defined as a 25–50% reduction in papular size or number. No improvement was defined as less than a 25% reduction in papular size and number.
Degree of improvement was also assessed by the patients by a five-point scale questionnaire during the follow-up visits as follows: −1: adverse effects (textural changes, pigmentary changes), 0: no improvement (<25% decrease in the size or the number of lesions), 1: mild improvement (25–50% decrease in the size and the number of lesions), 2: moderate improvement (50–75% decrease in the size and the number of lesions), and 3: complete clearance of the lesions (>75% decrease in the number of lesions).
Patients were also asked to report any of the following if experienced: pain, redness, crust formation, and hypo/hyperpigmentation. Patients were followed up at 3 and 12 months after the last treatment session.
The data files were imported into the Statistical Analysis System (SAS Institute Inc., Cary, North Carolina, USA) for data analysis. Data were presented as mean±SD for continuous data and as frequency and percentage for categorical data. χ2 and Fischer’s exact tests were used for categorical variables whereas continuous outcome variables were analyzed in mixed repeated-measure analysis of covariance models by SAS Proc Mixed.
The dependent variable was the number of lesions before treatment and after one and two treatment sessions. The independent variables of treatment session, sex, and skin type were included as classification variables.
The model included treatment session, age, sex, Fitzpatrick skin type, and the interaction between skin type and sex.
A P level ≤ 0.05 was used to indicate significance in all models.
Sixty patients were included in this study, 39 women and 21 men, mean age 47.7±6.67 years. Of the 60 patients enrolled initially, no one withdrew from the treatment sessions and all completed the 3-month follow-up period. However, only 52 patients presented at the 12-month follow-up.
A total of 516 lesions were treated. The average number of lesions before the initiation of the treatment in each patient was 8.6±3.69, which decreased to 2.53±1.81 lesions on average after the first session, with a significant difference (P<0.05), and to 0.2±0.55 at the first follow-up visit, after the second session, in 3 months, with a significant difference (P<0.05), compared with the improvement after the first session, which was maintained at the 1-year follow-up visit (Table 1). After each treatment session, patients experienced mild erythema and minimal discomfort mainly at the site of the treated lesions; this was followed by a fine crust that was observed after 5–7 days.
Complete clearance was observed in only one patient after the first session. After the second session, at the 3-month follow-up, complete clearance was observed in 54 (90%) patients as shown in Fig. 1a and b, whereas marked improvement was observed in six (10%) patients as shown in (Fig. 1c–f). No significant side effects were reported during the entire follow-up period. Focal postinflammatory hypopigmentation was observed in only five patients, mainly of skin type V and VI, as shown in Fig. 2a and b that faded gradually and disappeared without any topical medications before the first follow-up visit at 3 months. No recurrence was observed at the 12-month follow-up visit.
Results of the patients’ self-assessment showed a mean score of 2 (50–57% improvement) at the first follow-up visit and 3 (>75% improvement in the size and number of the lesions including complete clearance) at the second follow-up visit for all patients.
For the blinded photographic assessments, all three reviewers correctly identified the chronology of all participants’ photographs (60/60). The results of the blinded photographic assessments indicated clinically significant improvements in the lesions, with mean scores (based on all three reviewers) of 3 (>75% improvement in the size and the number of lesions including complete clearance) for all patients. None of the reviewers indicated an improvement or the presence of adverse effects in the post-treatment photos.
Patients with skin types IV and V showed a marked improvement compared with those with skin type VI while controlling for all other variables. Patients with skin type IV and V improved significantly following the first and the second session of treatment, but the magnitude was not different between the two.
There was a statistically significant difference on comparing the number of lesions before the treatment and after one laser session and also between after one session and after the second laser session.
Although initial descriptive statistics suggested a difference and a possible role for age and sex, the final model showed no significant effect of any of these.
The interaction between sex and skin type exerted no effect on the degree of improvement Table 2.
Treatment options for DPN have included cryotherapy, electrodesiccation, and curettage. Such options of treatment may cause unsatisfactory cosmetic results, including scarring and postinflammatory hyperpigmentation or hypopigmentation. They can also cause patient discomfort requiring anesthesia before treatment 6,7.
Nonablative laser treatment of DPN has been reported in a few studies with positive results. Garcia et al.8 compared the efficacy and complications of pulsed dye laser therapy for the treatment of DPN with those of curettage and electrodesiccation. They had concluded that the efficacy of pulsed dye laser in the treatment of DPN is not significantly different from the already established treatment modalities of electrodesiccation and curettage.
Schweiger et al.9 reported two patients with DPN who achieved an excellent cosmetic result following a single treatment with a long-pulsed 1064 nm Nd:YAG laser.
Yousif et al.10 proved that the use of a continuous-wave Nd-YAG laser 1064 nm with certain parameters could yield excellent or very good results in the treatment of DPN.
Nd-YAG laser is one of the most versatile and interesting lasers in dermatological laser medicine. Almost no other laser has such a wide spectrum of applications. Depending on wavelength (1064 nm) and mode (continuous, Q-switched, long pulsed), it is applied on benign pigmented, vascular lesions and hair reduction 11,12 because of the fact that 1064 nm is absorbed by all the skin chromophores. There have been reports of the use of a long-pulsed Nd-YAG laser as an effective line of treatment for plane warts 13, vascular lesions such as telangiectasia and venous lakes 14, and also in the treatment of atrophic scarring and post chickenpox scarring in patients with darker skin types 15,16. All these led us to use this laser for thermal destruction of DPN. Unlike other treatment modalities, there was no wound, thus avoiding prolonged postoperative pain, scarring, or downtime. Patients tolerated the procedure well; there was no need for topical anesthesia only in certain sensitive cases. The tendency toward pigmentary changes was temporary because of the lower absorption coefficient of melanin and less collateral epidermal damage 17. As an outcome, we achieved excellent cosmetic results after two treatment sessions without any side effects and no recurrence after 12 months of follow-up of 60 patients with DPN. Our results confirm the efficacy and safety of a long-pulsed Nd-YAG laser that had been reported by a case study of Schweiger et al. 9 as treatment sessions led to a statistically significant effect on the number of lesions as the first laser session significantly reduced the number of lesions. Furthermore, the second treatment session also reduced the number significantly from the first session. Both the patients and the evaluators reported complete disappearance of the lesions or marked improvement in the size and numbers of the lesions at the 12-month follow-up visit.
Skin type plays a significant role in determining the magnitude of the effect of treatment as patients with skin types IV and V showed a marked improvement compared with those with skin type VI. This could be explained by the fact that in skin types IV and V, the contrast between the color of the normal skin and that of the lesion is significant; thus, the treatment could be carried out effectively without the higher risk of complications such as pigmentary changes or scarring. However, in skin type VI, normal perilesional skin might have the same color as the lesion. The lack of contrast requires the operator to be more conservative with the laser energy to avoid damaging the skin. Another factor that may play a role is the significant absorption of the laser energy by the epidermal malanocytes that exhaust the laser energy before reaching the target chromophore. This phenomenon occurs more in darker skin phototypes.
These factors might explain the better response in patients with skin types IV and V compared with skin type VI.
As our results indicate that the number of lesions dropped significantly after one session, we recommend performing two laser sessions for the lesions that did not disappear completely as there was a statistically significant difference not only between the number of lesions before the treatment and after the first laser session but also between the number of lesions after one session and after the second laser session.
A long-pulsed Nd-YAG laser (1064 nm) can be considered an effective safe treatment modality for DPN. Two sessions are recommended for the optimum clearance of the lesions.
Conflicts of interest
There are no conflicts of interest.
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Keywords:© 2015 Egyptian Women's Dermatologic Society
dark skin; dermatosis papulosa nigra; laser treatment; Nd:YAG laser