A Case of Cutaneous Focal Mucinosis With Follicular Induction

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To the Editor:
I read with great interest the case report, titled “Cutaneous Focal Mucinosis Causing Follicular Induction of the Epidermis” by Tatsas et al,1 which was published in an issue of the American Journal of Dermatopathology. As I know, cutaneous focal mucinosis (CFM) is a very rare reason of follicular induction of the epidermis. Recently, I had the chance to observe a similar case.
A 52-year-old man with no notable medical history except diabetes type 2 presented with a lump on the abdominal skin 8 years ago. There was no history of previous trauma, tenderness, and pruritus. On dermatological examination, a reddish-colored nodule which was 0.9 cm in diameter was detected on the abdominal skin (Fig. 1). A shave biopsy was performed.
Histopathologic examination showed a polypoid lesion with a large mucin accumulation in the dermis containing spindled cells and stellate fibroblasts (Fig. 2). A minimal increase in the number of small-caliber blood vessels was observed. The overlying epidermis displayed immature hair follicle–like structures which extend from the epidermis into the myxoid connective tissue. They exhibited prominent retraction artifact and resembled closely a superficial basal cell carcinoma (Figs.2, 3). Based on these histological features, the diagnosis of CFM with follicular induction of the epidermis was established.
CFM is a type of localized dermal mucinosis clinically presenting as an asymptomatic skin-colored papule or nodule.2 Histologically, a localized ill-defined focus of mucin deposition between collagen bundles in the dermis is observed.3 The subcutis is rarely involved. Spindle-shaped fibroblasts are the predominant cell type, and they are claimed to be the major source of hyaluronic acid produced in the connective tissue.4
The term “follicular induction” has been used to delineate the epidermal changes overlying a dermatofibroma.2 In addition, it could be seen in many other lesions (Table 1).1,2,5,6 However, only a few cases of CFM with follicular induction have been reported until now.1,3,5
The etiopathogenesis of CFM is unclear, but it is thought to represent a reactive lesion. Although trauma may be a triggering factor, it has not been proven.7 Some authors suggested that mesenchymal cells located in the upper dermis may act as embryonic mesenchyme and lead to follicular germ induction.2 It is believed that local mediators, including epidermal growth factor released from mesenchymal cells, activate keratinocytes to induce hair follicle formation.8,9
In conclusion, the case presented here clearly exhibits epidermal follicular induction overlying CFM, similar to the case previously reported by Tatsas et al.1 Follicular inductive changes can rarely be observed overlying CFM and may be underrecognized, thus it may cause a diagnostic pitfall in superficially sampled lesions. It is important to be aware of this association, and to consider it in the differential diagnosis of some entities, such as superficial basal cell carcinoma and dermatofibroma with myxoid change.
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