Dermal melanocytosis includes several benign pigmented lesions which present as blue-gray color which is a result of the color transmission of melanin pigment through the dermis. While some types are present at birth, there is an acquired variant, acquired dermal melanocytosis (ADM), which usually involves faces of middle-aged Asian women. To the best of our knowledge, there are limited reports of extra facial ADM which all are on the trunk and extremities. Herein, we report a unique case of extra facial ADM affecting the scalp of a middle-aged man and provide a review of all extra facial ADM cases that have been reported.

© 2022 The Author(s). Published by S. Karger AG, Basel

Dermal melanocytosis includes several benign pigmented lesions that are clinically characterized by the gray or blue-gray color which is a result of the color transmission of melanin pigment through the dermis [1]. The presence of intradermal dendritic, pigmented, spindle-shaped melanocytes is the characteristic histologic finding of this group of lesions [2]. While some of them, like congenital dermal melanocytosis (Mongolian spots), nevus of Ito, or nevus of Ota are usually present at birth, others like blue nevus and nevus of Hori can appear in childhood or later in life [1]. There is a rare acquired variant, termed acquired dermal melanocytosis (ADM), which is most frequently seen on the faces of middle-aged Asian women. However, there are rare reports of extra facial ADM on the trunk and extremities [3]. In this article, we present an ADM appearing on the scalp of a middle-aged man. We also review reported cases with extra facial ADM until 2022.

A 50-year-old man, with a history of androgenetic alopecia since 8 years ago, presented with a hyperpigmented lesion on his scalp (shown in Fig. 1). He had noticed it 3 months prior to the time he visited our clinic and was confident it was a new-onset lesion. He also did not have such lesions elsewhere in the body. He was otherwise healthy and was not on any medication and also denied any history of inflammation, contact with chemicals and metals, or trauma to the scalp. The family history of same lesions was negative. Physical examination of the scalp revealed male pattern androgenetic alopecia (grade 3 according to Hamilton-Norwood classification) and a blue-gray, nonpalpable patch darker than the surrounding skin with no inflammation or scale on the vertex of his scalp. The skin examination of other sites of the body, including face and neck, trunk, and the extremities, was normal. Mucous membranes and other hair-bearing areas of the body showed no abnormality on physical examination.

Blue-gray nonpalpable patch on the scalp of a 50-year-old man.

A biopsy specimen was obtained and histopathological examination was done considering lichen planus pigmentosus, lichen planopilaris, melanoma, and post-inflammatory pigmentation. Histopathologic examination of the lesion showed normal epidermis with sparse, scattered, dendritic melanocytes and melanophages in dermis (shown in Fig. 2). These dendritic cells showed positive staining for melan-A by immunohistochemistry (shown in Fig. 3).

Diffusely scattered dendritic melanocytes and melanophages in dermis (H&E, ×100). The inset shows more details (H&E, ×400).

Immunohistochemistry demonstrates positive staining of the dendritic cells for melan-A (×100). The inset shows more details (×400).

Dermal melanocytosis is defined by the presence of spindle-shaped melanocytes in the dermis and clinically results in gray or blue pigmentation depending on the location of the melanocytes in the dermis. Dermal melanocytoses include several distinct clinical entities which are differentiated by the distribution, age of onset, and the tendency to fade spontaneously over time [2, 4]. It has been claimed that, at birth, melanocytes may be present in the dermal portion of the skin of the scalp, the backs of the hands, and the sacrum, but they disappear shortly after birth. There is a theory suggesting that dermal melanocytoses appear when melanocytes fail to migrate from the neural crest during the embryological development and do not reach their final location in the basal layer of the epidermis [5].

Congenital dermal melanocytosis (Mongolian spot) usually presents at birth and generally regresses spontaneously during childhood and is almost always located on the lumbosacral area or buttocks. More than half of nevi of Ota and Ito are present at birth and the remainder mostly appear around puberty and persist for life. Ota’s nevus is usually unilateral and follows the distribution of the first two branches of the trigerminal nerve and the area involved by Ito’s nevus usually corresponds to the distribution of the lateral supraclavicular and lateral brachial nerves [6, 7].

Although most dermal melanocytoses are congenital or appear during the childhood or adolescence, there is a rare group with a clearly acquired onset, known as ADM [2, 4]. ADM is most frequently seen in young and middle-aged Asian women and commonly appears bilaterally on the face. It is usually considered to be acquired bilateral nevus of Ota-like macules (ABNOM). The lack of ocular and mucosal membrane involvement distinguishes ABNOM and ADM from nevus of Ota.

Mataix et al. [2] classified ADM into two groups, facial and extra facial variants, and reported the cases with extra facial ADM until 2007. They also demonstrated that extra facial ADM showed a predilection for men and had a late age of onset. However, Lee et al. [3] reported that both extra facial ADM and ABNOM demonstrated a predilection for women and had a middle-age onset. There have been more reports of uncommon forms of extra facial ADM on the trunk and extremities ever since. Table 1 reviews reported cases with extra facial ADM until 2022, including the current case. In our case, the clinical presentation and the histologic examination suggest the diagnosis of dermal melanocytoses. Since the patient had been almost bald for 8 years and his wife, who first noticed the hyperpigmentation, was confident that the lesion was recently acquired, it is suitable to consider this, a late-onset ADM on the scalp. To our knowledge and based on search using keywords we did in several databases including Embase, MEDLINE, Web of Science, and Google Scholar, our case is the first reported case of extra facial ADM on the scalp.

Summary of the reported cases of acquired dermal melanocytoses with extra facial involvement and histopathological confirmation

The etiology of ADM is unknown, although several hypotheses have been proposed regarding the origin of melanocytes in the dermis: (i) melanocytes descending from the epidermis; (ii) the migration of hair bulb melanocytes; and (iii) the reactivation of latent dermal melanocytes by inflammation, local trauma, sex hormones, or some unknown agents. According to the distribution of the pigmented lesions of ADM, sun damage could also play a role in the pathogenesis [8, 9]. Since our case denied any history of trauma, inflammation, or contact to chemicals and did not use photo protection on the bald area of his scalp, we assume that in our case photo damage could act as a stimulus for reactivation of latent dermal melanocytes.

This case report was reviewed and approved by the bioethics committee of Isfahan University of Medical Sciences, approval number IR.MUI.MED.REC.1399.688. Written informed consent was obtained from the patient for publication of this case report and any accompanying images.

The authors have no conflicts of interest to declare.

The authors received no financial support for the research, authorship, and publication of this article.

Fatemeh Mohaghegh: visited and examined the patient and formed diagnostic and therapeutic plans for the patient and has also been involved in drafting the manuscript and revising it critically for important intellectual content. Parvin Rajabi: performed histologic examination on the biopsy specimen. Samin Nabavinejad: has been involved in collecting information from the patient including the pictures and preparing the biopsy specimen. She also participated in drafting the manuscript. Elham Tavousi Tabatabaei: taking an accurate history, contributing to the writing of the article, writing the largest share of the report, and involving in the patient’s care and final approval of the version to be submitted.

All data generated or analyzed during this study are included in this article. Further inquiries can be directed to the corresponding author.

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