Childhood longitudinal melanonychia: case series from Poland

Introduction

Longitudinal melanonychia (LM) also known as melanonychia striata is defined as a grey to black pigmentation of the nail plate due to the presence of melanin caused by hyperplasia or activation of nail matrix melanocytes [1]. The most important clinical aspect of LM is the association with the nail apparatus melanoma (NAM). It is estimated that approximately 76% of cases of this neoplasm presents initially as LM [1, 2]. NAM represents from 0.7% to 3.4% of all diagnosed melanomas in the Caucasian population. Rarity of this entity and non-specific clinical presentation contribute to the delay of the treatment due to inaccurate initial diagnosis. This determines worse prognosis in comparison to cutaneous melanoma [3].
The incidence of LM depends on genetically determined differences in the number and activity of melanocytes localized in nail apparatus. LM is relatively common in Afro-American, Japanese and Latino population. According to literature data, the occurrence of LM in Caucasian population does not exceed 1%. LM is rarely observed in children [1–5]. In the Polish literature this medical issue has not been reported yet.

Aim

To present the largest series of childhood LM in the Central and Eastern European population.

Material and methods

We analysed 348 patients who have been diagnosed with various nail pigmentation in 2010–2016. In adults, 64 cases of LM have been identified (including 3 cases of NAM; 4.7%), whereas 8 cases of LM have been identified in children (< 16 years of age). The latter were included in the further detailed analysis. Final diagnosis was established according to clinical, dermoscopic (onychoscopic) and histopathological evaluation.

Results

Clinicopathological and dermoscopic features of the analysed cases are summarized in Table I (Figures 1–4). Mean age at diagnosis was 9 years (range: 6–13), whereas the mean age of LM onset was 6.6 years (range: 4–10). There was no personal or family history of melanoma in the studied group. All children were otherwise healthy. No preceding trauma, history of medications intake or pigmentation-related disorders were reported.
The most common location of melanonychia was the left first fingernail. Mean width of the pigmented band was 4.3 mm. In 2 cases, pigmentation involved > 50% of the nail plate; in 3 cases, > 30% of the nail plate. The Hutchinson sign was present in one case, and pseudo-Hutchinson sign in 6 cases. Nail dystrophy has not been observed. Dermoscopically, the colour heterogeneity of longitudinal lines within a band was present in 5 cases; the irregularity of longitudinal lines thickness was present in 5 cases and irregularity of parallelism in 5 cases.
In 3 patients, the histopathological examination was performed after initial evaluation. In 1 patient (patient 1, Figure 1 A), after considering the doubtful character of the lesion, mother’s anxiety and size of the lesion, a decision of total excision of the nail apparatus was made. The procedure was performed in conduction anaesthesia. The nail apparatus was excised in one piece, the wound was covered with full-thickness skin graft taken from the inguinal area. The postsurgical period was uncomplicated. Further aesthetic results were satisfying (Figure 1 B). Histopathological examination revealed the presence of nail matrix nevus.
In 5 patients, the regular follow-up was recommended. In patient 2, spontaneous regression of LM was observed. Clinical examination at the first visit revealed 3 mm wide brown longitudinal streak of the right fifth fingernail; after 6 months, previously observed pigmentation was absent (Figures 2 A, B).
In patient 7, after 13-month follow-up, based on the worrying change in clinical and dermoscopic presentation (Figures 4 A, B), a decision of total excision of the nail plate was made. Histopathological examination revealed the presence of melanocytic proliferation of the lentiginous pattern along the dermoepidermal junction (Figures 5 A, B).

Discussion

LM incidence in the Caucasian population is estimated to be approximately 1% [3]. Nevertheless, authors’ observations indicate a much lower frequency of this lesion. The overstatement of the data may result from inconsistency of nomenclature. Some researchers classify lesions with non-melanocytic origin (e.g. subungual haemorrhage) into a group of melanonychia [5, 6]. Independently of the studied population, LM in children occurs very rarely. In Chinese research performed by Leung et al. [7], among 461 examined patients aged up to 19 years, no LM cases have been found. In our material, among 348 patients consulted due to various nail apparatus pathologies, 72 cases of LM have been identified, including 8 cases of childhood LM (2.0%).
The relationship between LM and NAM is currently undeniable. Even though the optimal patient management has not been established yet, most authors recommend histopathological evaluation of the disorder [8, 9]. Unfortunately, it is a painful procedure associated with the risk of permanent nail deformation. Therefore, in childhood LM the biopsy is performed in cases suspected of melanoma or on the parents' request.
The prediction of the course of LM in children is challenging. Although melanoma represents up to 2% of all diagnosed cancers in children, NAM is very rare. Unfortunately the disease, if occurs, is characterized by high mortality [10].
Goettmann-Bonvallot et al. [11] analysed 40 cases of LM in patients aged less than 16 years. The study identified 19 nevi (17 junctional and 2 compound), 12 lentigines and 9 cases of melanocytes activation as the background of LM. Similarly, Tosti et al. [12] and Léauté-Labrèze et al. [13] did not observe melanoma in 22 and 8 children with LM, respectively. Ohn et al. [14] analysed 58 nail matrix nevi in 56 children and concluded that nail matrix nevi in children significantly more often reveal melanoma-associated features like: multicolour pattern, darker discolouration, pseudo-Hutchinson sign, triangular sign, and the presence of dots/globules.
There are no definite recommendations regarding the management of childhood LM, therefore in our material, dermoscopic indications to biopsy were the same as in adults: the presence of Hutchinson sign, width of the pigmented band > 1/3 of the nail plate width, dark-brown colour of the background and irregular dermoscopic pattern (various colours and thicknesses of the longitudinal lines with uneven intervals) [15]. Another important factor was the change in clinical and dermoscopic presentation, which implicated prompt histopathological evaluation in patient 7.
In the literature some cases of spontaneous regression of childhood LM have been described [16–18]. Murata and Kumano [17] showed that randomly distributed dots and lines that follow the melanocytic lines may be indicators of spontaneous fading of LM in children. In our material, we did not observe these structures in a patient with spontaneous regression.
Our observations and literature data strongly support the rarity of childhood NAM in Caucasian population. To the best of our knowledge, only 15 cases (including 3 that occurred in fair-skinned Caucasians) of NAM in children have been reported so far. Most childhood NAMs described so far presented clinically as LM; the histopathological examination confirmed the diagnosis of melanoma “in situ” (Table 2) [19–29]. Nonetheless, in 2 cases, melanoma had an aggressive course [26]. Interestingly, these both cases did not present as LM, what indicates indirectly that nail matrix melanocytes were not the origin of melanoma.
The difficulties in interpretation of the histopathological picture of nail apparatus pigmentation disorders are being emphasized. Some aspects, considered in adults as evidence of malignancy (e.g. nucleus atypia, moderate migration of melanocytes), may be present in benign pigmented lesions in children, what we present in patient 7 [19, 20, 26, 30, 31]. In Goettmann-Bonvallot et al. report [11], nuclear atypia and moderate migration of melanocytes were observed in 15% and 20% of cases, respectively. The fact brings into question 4 cases of NAM diagnosed by Kato et al. [22] and Kiryu [23]. Recently, Bonamonte et al. [28] mentioned a possible utility of a novel immunohistochemical marker, anti-p16, in such cases.

Conclusions

In the light of presented facts, the risk of childhood NAM in Caucasian population appears to be low. The presented cases seem to support the thesis of benign background of LM in children. Histopathological evaluation or removal of the lesion does not seem to be reasonable in every case. Nevertheless, regarding the rarity of this entity (especially in Caucasian population), difficulty in predicting the evolution of the lesion, and the possibility of development of NAM in adults with LM observed since the childhood, regular long-term follow-up should be recommended. Dermoscopy is useful in initial and subsequent patient assessment.

Conflict of interest

The authors declare no conflict of interest.

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