Progressive Pigmented Lesions in a Healthy Adolescent

An otherwise healthy 14-year-old Caucasian girl was referred due to asymptomatic hyperpigmented macules (Figure 1) that had progressively developed over the past year. She did not have pruritus or accompanying systemic symptoms. The skin lesions were disseminated, predominantly involving the anterior neck, abdomen, torso, axillae, and inguinal folds. In the flexural regions, the macules displayed a slightly velvety surface. The face, palms, soles and mucous membranes were unaffected. The remainder of the physical examination, including vital signs, somatometry, physical growth and neurodevelopment, was normal. There was no preceding history of inflammatory or infectious lesions in the affected areas, nor trauma or any recent topical or systemic drug exposure. Laboratory investigations, including metabolic screening, were within normal limits. Skin biopsy revealed acanthosis and basal layer hyperpigmentation with the presence of dermal melanophages. No lichenoid infiltrate, basal layer vacuolar damage or increase in the number of mast cells was identified. Idiopathic eruptive macular pigmentation. Idiopathic eruptive macular pigmentation (IEMP) is a rare, benign and self-limiting pigmentary disorder, with fewer than 40 paediatric cases reported [1]. It occurs from 1 to 31 years of age, predominantly in childhood and adolescence, without sex predilection, mostly in Indian patients [2]. Its pathogenesis remains uncertain; hormonal factors and autoimmunity are thought to trigger melanosis [3, 4]. Clinically, IEMP presents as round or oval, well-defined, non-pruritic, homogenous brown macules and plaques, appearing without preceding lesions, mainly on the trunk, neck and proximal limbs, as in this case. Rare presentations include a Christmas tree pattern, confinement to flexures or a velvet-y surface [5, 6]. Dermoscopy typically reveals linear cristae cutis and sulci cutis [7]. Histopathology is nonspecific but supportive, showing acanthosis, basal layer hyperpigmentation and dermal melanophages [1], and rarely, pigmented papillomatosis [3] (Figures 2 and 3). The main differential diagnoses include friction melanosis, post-inflammatory hyperpigmentation, acanthosis nigricans and fixed drug eruption [2]. The absence of specific triggers, paired with normal somatometry and metabolic screening, ruled these out. Other acquired macular hyperpigmentation disorders of uncertain cause were considered (lichen planus pigmentosus, erythema dyschromicum perstans and ashy dermatosis) however, the absence of erythema, pruritus, basal cell damage or lichenoid infiltrate effectively excluded them [8]. IEMP and related idiopathic hyperpigmentation disorders remain diagnostic challenges due to overlapping clinical and histological profiles. However, awareness is key to avoiding unnecessary therapy. Prognosis is excellent, and spontaneous regression is expected [1], albeit gradual. We would like to thank Dr. Pedro de Vasconcelos for kindly providing the histological photographs included in this paper. The authors have nothing to report. The authors declare that the research presented in this manuscript adheres to the ethical principles outlined by Lisbon Local Health Unit Ethics Committee. All procedures involving human participants were conducted in accordance with the ethical standards of the Lisbon Local Health Unit and the Declaration of Helsinki (1964), as revised in 2013. Written informed consent was obtained from a parent of the patient for publication of this case report and accompanying images prior to the patient's passing. The authors declare no conflicts of interest. The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.