Follicular Induction And CK20+ Merkel Cells Overlying Cutaneous Focal Mucinosis

Background

Cutaneous focal mucinosis (CFM), or focal dermal mucinosis, is a benign reactive process categorized as a primary mucinosis. Skin biopsy is essential for diagnosis, as the clinical appearance is often non‐specific. Follicular induction is a phenomenon whereby the epidermis is induced by an underlying process to form primitive or mature hair follicles, and is commonly seen overlying dermatofibromas. Follicular induction has been rarely described in CFM.

Methods

We performed a retrospective histologic review of lesions of CFM confirmed by skin biopsy from 2010 to 2015 in our department.

Results

We found that 11% (11/98) of CFM lesions demonstrated follicular induction. CK20 immunostaining was performed on 4 of these biopsies and highlighted an increased density of CK20+ Merkel cells within the basaloid epidermal proliferations.

Conclusions

As superficial basal cell carcinomas (BCC) often demonstrate a mucinous stroma around the basaloid islands, CFM with follicular induction may closely mimic a BCC histologically, particularly in superficial shave biopsies. Therefore, it is important that dermatopathologists be aware of this phenomenon. Furthermore, CK20+ staining within the basaloid epithelial proliferations may be helpful in differentiating CFM with follicular induction from a BCC.

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