Cutaneous focal mucinosis causing follicular induction of the epidermis

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 histological 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 showed follicular induction. Cytokeratin 20 (CK20) immunostaining was performed on all 11 of these biopsies that showed follicular induction and highlighted an increased density of CK20+ Merkel cells within the basaloid epidermal proliferations.

CONCLUSION

As superficial basal cell carcinomas (BCC) often show 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.

Primitive follicular induction in molluscum contagiosum

BACKGROUND

Molluscum contagiosum (MC) is the commonest human poxvirus infection. Follicular induction has rarely been observed in the epidermis surrounding lesions of MC. A virus-induced localized proliferation of germinative/stem cells of the folliculosebaceous-apocrine unit has been suggested as the underlying cause, however few reports of this peculiar phenomenon exist in the literature and the mechanisms involved in this proliferation require further study.

METHODS

We prospectively collected MC cases showing multifocal areas of primitive follicular induction involving the adjacent undersurface epidermis. Immunohistochemical expression of BerEP4, PHLDA1 and cytokeratin 20 (CK20) was evaluated in the basaloid germs surrounding the lesions. For PHLDA1, we used epidermal melanocytes as a positive internal control. For BerEP4, we employed a basal cell carcinoma (BCC) and for CK20, colon as positive external controls. An incubation without the primary antibody functioned as an external negative control.

RESULTS

All the cases studied showed an intense positive staining of the basaloid buds with BerEP4 and weaker stain for PHLDA1. CK20 showed the presence of scattered Merkel cells within the induced epidermal basaloid proliferations favoring their reactive origin.

DISCUSSION

The pathogenetic mechanisms behind the development of these microscopic features and the link between follicular induction and poxvirus infection are explored. Awareness of this unusual phenomenon by dermatopathologists will be helpful in avoiding a misdiagnosis of a superficial BCC in such cases.

CONCLUSIONS

BerEP4 and PHLDA1 were consistently expressed in the areas of primitive follicular induction surrounding lesions of MC. CK 20 stained the Merkel cells present in the basaloid buds. All these findings support the reactive origin of this phenomenon, which we believe is most probably viral-induced.

Trauma-Induced Cutaneous Focal Mucinosis of the Mammary Areola: An Unusual Presentation

Cutaneous focal mucinosis (CFM) is a localized form of cutaneous dermal mucinosis clinically presenting as an asymptomatic skin-colored papule or nodule. The etiopathogenesis of CFM is unclear, but it is thought to represent a reactive lesion. Although trauma has been suspected as a triggering factor, it has never been proven in cases of CFM. We report 2 male patients with trauma-induced CFM arising at the mammary areola, which is an unusual site for CFM. Both male patients presented with a solitary nodular lesion of up to 2 cm in diameter at the right areola. Histology was characterized by circumscribed abundant dermal mucin deposits in a polylobulated pattern without an increased number of fibroblasts or capillaries and with absence of an inflammatory infiltrate. Alcian blue stain at pH 2.5 highlighted the mucin deposits. Immunohistochemistry showed partial expression of FXIIIa by 30% of the stromal cells, but no reactivity for CD34, smooth muscle actin, desmin, CD68 and S-100. A history of trauma (laser-based epilation, piercing) preceded the development of CFM in both patients. Surgical excision resulted in complete remission without recurrence. Follow-up in both our patients did not reveal recurrences. CFM has to be distinguished from benign and malignant myxoid neoplasms.