Discussion
SOCs are a rare, usually asymptomatic, nail abnormalities which are
diagnosed incidentally in the progress of investigating other diseases
like melanomas. Previous studies have described the possibility of an
association between SOC and trauma, clubbing, and subsequently cyst
formation. Clubbing can affect the dermis of the nail by fibroblast
proliferation which causes cyst formation. Age, sex, lesion site,
differential diagnosis (macroscopic and microscopic), underlying
diseases, and treatments are listed in Table 1 of previous cases in this
field.
SOCs may have different clinical presentations, including onycholysis,
onychodystrophy, pigmentation of the nail bed, ridging, and thickening.
It most commonly affects single digits, mainly thumbs and great
toenails, and pain is not uncommon (3).
The subungual epidermoid inclusions that Lewin first referred to as the
follicular microcysts of the nail bed are bulbous proliferations of the
extremities of rete ridges, occasionally with the development of
microcysts (4). These microcysts seldom lose their attachment to the
nail bed epithelium and appear superficially within the dermis. The
production of homogeneous keratin without a granular layer characterizes
the keratinization of this superficial epithelial inclusion. The cyst’s
epithelium also mimics the follicular isthmus (4).
Onycholemmal is the new term that is being used in literature. It
depicts a specific type of subungual tumor with a pattern of
onycholemmal microcysts and trichilemmal keratinization (5). All of
these results point to the presence of vestiges of follicular units in
the nail bed epithelium. In contrast to palms and soles, the nail
epithelium is an invagination of the dorsal epidermis overlaying the
digit that includes a few hair germs, consistent with embryology. The
clinical presentation in our index case included onychodystrophy and
onycholysis on a nail of the second right finger with no history of
recent trauma, pain, or bleeding. Subungual melanomas and onycholemmal
carcinomas can mimic SOC presentations and nail bed biopsy is required
for appropriate diagnosis (2).
On histopathology, onycholemmal cysts originate from the nail bed
epithelium and are restored with eosinophilic keratin in the absence of
a granular layer. The follicular isthmus outer root sheath is homologous
to SOC and it is keratinized with no granular layer (6). The nail bed
biopsy with partial or total nail avulsion is required for appropriate
diagnosis.
The differential diagnosis of onycholemmal cyst include subungual
keratoacanthoma. squamous cell carcinoma (SCC), verrucous carcinoma
(VC), glumus tumor, subungual metastasis and onycholemmal carcinoma. The
characteristic histological findings can help the exact diagnosis of
these lesions.
There are no specific treatment recommendations (3). The biopsy from the
affected area revealed multiple free-lying cysts within the dermis of
the nail bed, and in the near region to the epithelium of the nail bed.
The cysts were lined by the stratified squamous epithelium with no
granular layer or any cellular atypia. The cysts included luminal
onycholemmal keratin (3).
This report highlighted the variable clinical presentations of subungual
onycholemmal cysts (SOC), which can mimic different nail malignancies,
including subungual melanomas and onycholemmal carcinomas. Early
diagnosis of SOC by nail biopsy can improve the treatment outcome.