Localized and asymmetrical acquired dermal melanocytosis (ADM) has been documented on the face or other areas of the body [1]. ADM is commonly observed in Asian women, with facial lesions being the most common presentation. However, ADM on nasal mucosa can occur in rare cases. Histopathological examination demonstrates irregularly shaped, bipolar melanocytes in the upper and middle dermis with no disruption to the normal skin architecture [2]. Various treatment approaches are available, including topical agents, cryotherapy, and laser therapy. Laser treatments offer precise targeting, minimal scarring, and potentially faster recovery times compared to traditional approaches. Here, we present a case of ADM on the nostril that was successfully treated with Q-switch neodymium-doped yttrium aluminium garnet (Nd:YAG) lasers. A written informed consent was obtained from the patient for the publication of this case report.

We present a 32-year-old female with a 5-year history of a hyperpigmented macule on her left nostril (Fig. 1A). The macule exhibited a blue to gray color and was devoid of any associated symptoms. The patient denied any history of local inflammation, trauma, or medication use. Furthermore, there was no reported exposure to metals or chemicals. However, the patient revealed a habitual behavior of frequent nose blowing and touching, due to allergic rhinitis.

Figure 1. (A) A solitary, 0.6 × 2.2 cm sized, blue-gray colored macular pigmentation on the left nostril. (B) Dermoscopic examination revealed homogeneous blue to gray colored macule. (C) A photo showing the disappearance of the lesion after 8 sessions of laser treatment. (D) Dermoscopic image showing the disappearance of the lesion after 8 sessions of laser treatment.

Physical examination revealed a localized, well-defined, blue to gray colored macule on the left nostril. Dermoscopic examination supported the diagnosis by demonstrating a homogeneous blue to gray colored macule (Fig. 1B). A skin biopsy was performed, and histopathological analysis revealed dendritic pigmented cells with fine pigments in the papillary and middle dermis (Fig. 2A, B). Immunohistochemical staining confirmed positive for Melan-A, and the brown pigment stained positive with Fontana-Masson stain, which is indicative of melanin in dermal melanocytes (Fig. 2C, D).

Figure 2. (A) Many spindle or dendritic pigmented cells in the papillary and middle dermis (H&E, ×100). (B) Several dermal dendritic pigmented cells (H&E, ×200). (C) Dendritic melanocytes in the upper dermis stained positive on Melan-A (H&E, ×200). (D) Fontana-Masson stain highlights melanin pigment in dendritic melanocytes (H&E, ×200).

The patient underwent a series of eight sessions of 1,064 nm Q-switched Nd:YAG laser (Spectra Laser; Lutronic) treatment, with topical anesthesia applied 30 minutes prior to each session. A spot size was 6 mm and a mean fluence was 3.6 J/cm² (range, 3.2-4.0 J/cm²). The laser energy was irradiated two passes at a pulse rate of 5-10 Hz. The laser treatment was well-tolerated, and intervals of mean 3.3 weeks (range, 2-5 weeks) were maintained between sessions. Remarkably, the pigmentation showed complete remission after the completion of 8 sessions of the laser treatments, and no adverse events such as scarring or depigmentation were observed. Subsequent four-month follow-up demonstrated no signs of relapse. Subsequent four-month follow-up demonstrated no signs of relapse (Fig. 1C, D).

In the Asian population, the occurrence of ADM on the nose is not uncommon. According to Murakami et al. [3], 30.4% of their patients had ADM localized on the nose, characterized by asymptomatic blue-brown or slate-gray macules [4]. However, there is limited published literature regarding ADM specifically in the nasal mucosa. It is important to differentiate ADM from post-inflammatory hyperpigmentation (PIH) and, if localized only to the nose, melanoma should be excluded as a primary concern [4]. Dermoscopy and histological examination are recommended when doubt arises, revealing the presence of dendritic or elongated melanocytes in the upper- and mid-dermis [5]. Histologically, PIH exhibit dermal melanin and melanophages but lack dermal melanocytes, implying distinct treatment requirements [4].

The development of ADM is not yet fully understood, and several hypotheses have been proposed. One suggests that dermal melanocytes may migrate from the basal layer of the epidermis or hair bulbs to the dermis later in life. Another theory involves immature melanocytes failing to migrate from the neural crest to the basal layer during embryological development, leading to their retention in the dermis [6]. The condition is often associated with factors like contactants, inflammation, trauma, or repeated frictions. In this case, the patient’s habitual nose picking and manipulation may have served as contributing factors to the development of ADM [4]. Alternatively, the melanin-synthesizing ability of dermal melanocytes may increase more slowly compared to typical nevi without any precipitating factors [6].

The first reported treatment of ADM was cryotherapy [7], but it showed unpredictable outcomes with a high risk of permanent scarring and hypopigmentation. Dermabrasion was used by Kunachak et al. [8] with successful results; however, this approach is invasive. Presently, Q-switched lasers are the main treatment option for ADM, as well as nevus of Ota [9]. The Q-switched mode enables the emission of extremely high energy within a brief timeframe, and causes selective melanocyte injury through acoustic shockwaves. The 1,064 nm wavelength is mainly selectively absorbed by melanin-containing chromophores and can penetrate deep in the dermis [8].

Though several studies have been done on the treatment of ADM with Q-switched Nd:YAG laser, there is no clear consensus on the correct protocol (Table 1). The parameters used in ADM with the Q-switched Nd:YAG laser were 1,064 nm wavelength, 3-5 mm spot size, and a mean fluence of 4-10 J/cm² [10-13]. When compared to the typical low-fluence laser toning mode, a smaller spot size and higher fluence are applied. In more than half of the cases, patients achieved good or excellent results. However, particularly when treating lesions on the mucosa, more precise control is essential compared to general keratinized skin. In a study conducted by Limpjaroenviriyakul et al. [14] in Thailand, a 6 mm spot size with 3.5 J/cm² fluence was used for the removal of labial hyperpigmentation. The thinner, non-keratinized, and well-vascularized nature of the mucosa allows for enhanced penetration and more significant thermal effects. Consequently, our study also employed a smaller spot size compared to what is commonly used on other facial skin. Furthermore, given the potential risk of erosion and fibrosis in mucous membrane, the fluence needs to be adjusted to a lower level. In our case, excellent clearance was observed in 8 sessions of treatment with 6 mm spot size at a mean fluence of 3.6 J/cm².

Table 1 . Summary of literature on laser therapy for acquired dermal melanocytosis in Asian patients

Reference	Case	Diagnosis	Age (yr)	Location	Parameter/sessions	Result (%)	PIH
Polnikorn et al. (2000, Thailand) [12]	66	ABNOM	Mean 34	Zygomatic: 63 (95.5) Temporal: 8 (12.1) Nose: 2 (3.0) Forehead: 4 (6.1)	3 mm spot size 4-6 J/cm2	Good or excellent (50%)	48 (73)
Kunachak and Leelaudomlipi (2000, Thailand) [13]	70	ABNOM	Mean 37	Zygomatic: 70 (100)	4 mm spot size 8-10 J/cm2 Mean 2.8 sessions	CR (97.1%)	None
Lee et al. (2009, Korea) [11]	29	ABNOM	Mean 33.4	Zygomatic: 29 (100)	3 mm spot size 8.0-9.5 J/cm2 Mean 5.2 sessions	Good or excellent (66%)	2 (7)
Aurangabadkar (2019, India) [10]	1	ABNOM	-	-	5 mm spot size 4-5 J/cm2 5 sessions	-	None
Present case (2023, Korea)	1	ADM	32	Nasal mucosa	6 mm spot size Mean 3.6 J/cm2 8 sessions	CR	None

Values are presented as number only or number (%).

ABNOM, acquired bilateral nevus of Ota-like macules; ADM, acquired dermal melanocytosis; -, not mentioned in the article; CR, complete remission; PIH, post-inflammatory hyperpigmentation.

While Q-switched laser treatments have shown good clearance rates for ADM, they are frequently associated with post-treatment complications like PIH [8,9,12,13]. Higher degrees and frequencies of laser irradiation are associated with PIH occurring 2 to 4 weeks afterward [15]. Polnikorn et al. [12] and Kunachak and Leelaudomlipi [13] both used Q-switched Nd:YAG laser to treat ADM and reported that the rate of PIH was 73% and 50%, respectively. According to Momosawa et al. [15], using Q-switched laser for ADM without any pretreatments, PIH was almost consistently observed within 2 to 4 weeks after the initial laser treatment. Kunachak et al. [9] employed repetitive treatment sessions at 1- to 2-week intervals, performing the second laser session before PIH appeared, resulting in successful ADM clearance but a relatively high (5.7%) risk of hypopigmentation. Our repetitive treatment sessions were performed at a mean of 3.3 weeks (range, 2-5 weeks) intervals. This short interval time was chosen to improve the rate of clearing and prevent epithelial repigmentation. Furthermore, the application of a low-potency topical steroid was administered to prevent PIH.

In our case, Q-switched Nd:YAG laser treatment proved to be an effective and safe option, resulting in substantial clearance of the hyperpigmented macule without any adverse effects. The laser’s selective photothermolysis property targets melanin without causing damage to surrounding tissues, making it an appealing choice for treating dermal melanocytosis.

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Conceptualization: JSP, YJC. Data curation: JSP. Formal analysis: JSP, YJC. Investigation: JSP, YJC. Methodology: YJC. Project administration: YJC. Software: JSP. Validation: YJC. Visualization: JSP. Writing–original draft: JSP, YJC. Writing–review & editing: all authors.

Young-Jun Choi is the Editor-in-Chief of the journal, but was not involved in the review process of this manuscript. Otherwise, there is no conflict of interest to declare.

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