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Abstract
Seborrheic keratosis (SK) has long been known to be an acquired benign tumour of adulthood. Nevo-blaschkoid pattern of SK presenting during infancy is rare and puts a clinician in a quandary regarding final diagnosis. This hypothesis of paediatric SK being a subtype of epidermal nevus (EN) has muddled the understanding of both disorders. There are histopathological pointers that differentiate seborrheic keratosis from SK-like histology of EN. Here, we present a child with blaschkoid SK with onset during infancy. Dermoscopic evaluation showed comedo-like openings suggestive of SK. The benefits of performing shave biopsy were twofold. Diagnostic confirmation of it being SK and not SK-type of EN and therapeutic option of their simultaneous removal ensured prompt management.
- dermatology
- pathology
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Background
Seborrheic keratosis (SK) is a ubiquitous condition, occurring in nearly 100% of adults over the age of 50.1 Although advancing age is an independent risk factor for its development, its presence in young adults and paediatric population makes the nomenclature ‘senile keratosis’ redundant.2 Inherently a benign epidermal tumour, recent studies indicate a close association of SK with epidermal nevus (EN)3 due to a spectrum of postzygotic mutations noted in both conditions; especially fibroblast growth factor receptor 3 (FGFR3) and phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA).4 SK following cleavage lines has been reported but rarely along the lines of Blaschko. Here, we present a boy in middle childhood who presented with blaschkoid SK since infancy. Histopathological differences between SK and SK-like histology of EN have been documented and implemented in our case. With the aid of dermoscopy, we could build-up on our final diagnosis.
Case presentation
An otherwise healthy boy in his middle childhood was brought to dermatology outpatient department with multiple, asymptomatic, dark raised lesions over the right side of his neck that were present since the age of 1 year. A few showed steady increase in size. There was no involvement of ipsilateral upper limb or any other similar lesions elsewhere. He was born out of a non-consanguineous marriage with no other significant personal or family history.
On examination, multiple soft black, mulberry-shaped sharply demarcated raised papules, few showing a pedunculated base on the right posterior aspect of neck in a linear arrangement with a stuck-on appearance were seen (figure 1). Size varied from 1 to 5 mm. Skin over the lesions was waxy with a cerebriform surface. Intermingling skin was normal.
Multiple soft black, mulberry-shaped sharply demarcated raised papules with few showing a pedunculated base on right posterior aspect of neck in linear arrangement of varying sizes.
Investigations
Dermoscopic findings show cerebriform appearance with fissure and ridges (sulci and gyri) with comedo-like openings (figure 2).
Dermoscopy showing comedo-like openings, fissures and ridges on pedunculated papule (magnification 10×).
After written and informed consent was taken, shave excision was performed under local anaesthesia and pedunculated papules were sent for histopathological examination. Differential diagnosis of SK and keratinocytic EN was given. Histopathological findings confirmed acanthotic SK with acanthosis, papillomatosis, uniform basal layer pigmentation, horn cysts and pseudocysts (figures 3 and 4).
Histopathological findings using H&E staining show hyperkeratosis, acanthosis, papillomatosis, increased basal pigmentation, horn cysts and pseudocysts (magnification 10×). Note that the base of the lesion shows pedunculated base (red cross).
Histopathological findings using H&E staining show hyperkeratosis, acanthosis, papillomatosis, increased basal pigmentation, horncysts (green tick) and pseudocysts (yellow star) characteristic of seborrheic keratosis (magnification 40×).
Differential diagnosis
Linear SK and keratinocytic EN were considered. Although shared histopathological features noted in both are acanthosis, papillomatosis and variable degrees of hyperkeratosis and hyperpigmentation, we found a few histopathological differences between the two. Distinct histopathological and dermoscopic features led us to conclude our case as linear SK and not a type of epidermal nevi. Online supplemental table 13–12 tabulates broad differences between the two differentials.
Supplemental material
Treatment
With clinical, dermoscopic and histological concordance, counselling was done. Family of the child insisted on removal of the lesions for cosmetic purposes. Residual lesions were removed through radiofrequency ablation under local anaesthesia.
Outcome and follow-up
4 months after removal of lesions, no recurrence was seen. Shave biopsy site and sites where radiofrequency was performed healed well with no residual pigmentation. Family was, however, asked to carry out surveillance of the area well into adulthood.
Discussion
SK in young adults is not unknown,2 but its presence in paediatric population is rare. Few case reports of SK in children are reported, predominantly being dermatosis papulosa nigra-type.13
Advancing age and UV exposure are well-known risk factors for development of SK.1 Presence of amyloid precursor protein in lesions of UV-exposed skin in older age endorses this.13 Proposed multimodal mechanism of SK formation is elucidated by Sun and Halpern,13 however, none of them annotate for paediatric onset.
Genomic alterations implicated in SK are FGRF3 and PIK3CA mutations. Positive FGFR3/FOXN1 feedback loop in SK leads to epithelial differentiation. Enhanced phosphorylation of ERK1/2 and lower levels of apoptosis contributes to their permanence. Other oncogenes have also been implicated, although practical aspects of these associations are not fully elucidated. Presence of these mutations does not indicate malignant risk. Similar genetic markers shared by SK and EN make their association and origin more perplexing.4
Epidermal nevi constitute a type of mosaic disorders originating from postzygotic mutations that are present at birth in a linear pattern but can also present later in life.14 Concomitantly, published cases of segmentally arranged SK presenting at birth15 16 make diagnosis confusing. Although genetic drivers seen in both disorders show significant overlap, they are distinct disorders. Similar mutations can be present in malignancies and in benign conditions with zero malignant potential, making the foundation open to further elucidation.4
The dichotomy of SK is expansive. Its presence in extremes of age, although in varying degrees, to its presence along cleavage and blaschkoid lines; many questions still remain unanswered about this universal condition. Acute eruptive SK along lines of cleavage is reported in various neoplastic conditions (Leser-Trélat sign)14 some showing a raindrop pattern.17 Blaschkoid appearance of SK, however, does not represent a paraneoplastic entity and have not been associated with underlying malignancy.
Blaschko’s lines that represent normal developmental pathways of skin during embryogenesis have many nevoid and acquired conditions obeying its manifestation.18 Onset of these disorders can occur at birth, during childhood or adulthood depending on cell lineage, gene function and mutation timing.19
Prior reports of childhood onset, nevoid and blaschkoid SK have led to the confusion of it being a EN with SK subtype or classic SK (online supplemental table 2).10 15–18 20–23 Bassi et al,20 Yagerman and Marghoob15 and Akasaka and Akasaka16 have reported congenital, paediatric or adult onset of clinico-histopathological lesions along lines of Blaschko suggestive of SK with most having dermoscopic findings to corroborate the same. However, those authors implied the entity to be a subtype of epidermal nevi. We believe that morpho-histological picture of the lesion must be given preimminence over the duration or onset. Dermoscopy must be performed on such lesions to aid the diagnosis.
Supplemental material
Although benign, extensively distributed segmental SK has been reported to have secondary malignant changes well into adulthood. One report of segmentally arranged SK with impending atypia and squamous cell carcinoma10 and another with multiple fibroepithelial basal cell carcinoma associated with SK in a nevoid distribution have been reported.21 This necessitates further evaluation of extensive lesions.
As SK rarely resolves spontaneously and can continue to gradually increase in size,13 shave biopsy can serve as a therapeutic modality to manage case with an additional advantage of it being definitively differentiated from EN with SK-like histology. This is particularly helpful in cases with a diagnostic dilemma.
We are still yet to dissect the phenomenon of SK in segmental pattern or in paediatric population. But blaschkoid SK is a morphological subtype here to stay in its own right without the scepticism of it being a type of EN.
Learning points
Seborrheic keratosis in pediatric population showing a blaschkoid pattern results in a diagnostic dilemma where epidermal nevus is a close differential diagnosis.
Dermoscopy can aid in diagnosis and histopathological findings can differentiate between the two.
Shave biopsy can serve as a diagnostic and therapeutic advantage.
Blaschkoid SK does not signify any underlying malignancy and can be seen during childhood.
Ethics statements
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Supplementary materials
Supplementary Data
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Footnotes
Contributors The following authors were responsible for drafting of the text, sourcing and editing of clinical images, investigation results, drawing original diagrams and algorithms and critical revision for important intellectual content: SSH, AP and VS. The following authors gave final approval of the manuscript: SSH, AP and VS.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Case reports provide a valuable learning resource for the scientific community and can indicate areas of interest for future research. They should not be used in isolation to guide treatment choices or public health policy.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.