Dermatology: Practical and Conceptual Research Letter | Dermatol Pract Concept. 2023;13(2):e2023096 1 Frontal Fibrosing Alopecia Associated With Oral Erosive Lichen Planus: Two Locations, One Disease Francesco Toso1,2, Andrea Cortese1,2, Giovanni Fiorillo1, 2, Antonio Costanzo1,2, Riccardo G. Borroni1,2 1 Dermatology Unit, Humanitas Research Hospital - IRCCS, Rozzano, Milano, Italy 2 Department of Biomedical Sciences, Humanitas University, Pieve Emanuele, Milano, Italy Key words: alopecia, lichen, dermopathology, dermoscopy Citation: Toso F, Cortese A, Fiorillo G, Costanzo A, Borroni RG. Frontal Fibrosing Alopecia Associated with Oral Erosive Lichen Planus: Two Locations, One Disease. Dermatol Pract Concept. 2023;13(2):e2023096. DOI: https://doi.org/10.5826/dpc.1302a96 Accepted: July 27, 2023; Published: April 2023 Copyright: ©2023 Toso et al. This is an open-access article distributed under the terms of the Creative Commons Attribution- NonCommercial License (BY-NC-4.0), https://creativecommons.org/licenses/by-nc/4.0/, which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original authors and source are credited. Funding: None. Competing Interests: None. Authorship: All authors have contributed significantly to this publication. Corresponding Author: Francesco Toso, MD, Department of Biomedical Sciences, Humanitas University, Dermatology Unit, Humanitas Research Hospital – IRCCS, Via Rita Levi Montalcini, 4 20090 Pieve Emanuele, Milano, Italy. E-mail: francesco.toso@humanitas.it Introduction Frontal fibrosing alopecia (FFA) is a primary scarring alope- cia that mainly affects postmenopausal women and is clini- cally characterized by recession of the fronto-temporal line with loss of the eyebrows [1]. Case Presentation An 89-year-old woman presented to our dermatology unit for a localized burning sensation in the oral cavity for 3 months, that was treated with oral acyclovir without notice- able improvement. Family history included cutaneous lichen planus in her son. Personal history included arterial hyper- tension, osteoporosis, and rectal resection surgery for T2N0 rectal adenocarcinoma. Physical examination revealed a few erosions, partially covered by whitish pseudo-membranes, over an erythematous base on the oral vestibule and buc- cal mucosa bilaterally, where whitish striae referable to Wickham striae were also observed (Figure 1A). At the same time, a symmetrical eyebrow alopecia accompanied by a bi- lateral fronto-temporal hairline recession with loss of visible follicular ostia was noted (Figure 1B). Trichoscopic exam- ination showed rarefaction of follicular ostia, in the absence of active inflammatory lesions, yellow dots, or vellus hair (Figure 1C). A clinical diagnosis of frontal fibrosing alope- cia was then established. General examination excluded the presence of other lesions on the skin or concomitant lichen planopilaris. The patient laboratory tests were all within ref- erence range except for mildly increased ferritin and mild neutrophilia. A comprehensive serological autoimmunity panel gave negative results, while microscopic and culture examination of an oral cavity swab excluded the presence of bacteria or yeasts. Histopathologic examination of a biopsy specimen of the edge of an oral erosion showed a band-like lymphocytic infiltrate in the superficial chorion and at the junction with the overlying mucosa (Figure 1D), consistent with the diagnosis of oral erosive lichen planus. 2 Research Letter | Dermatol Pract Concept. 2023;13(2):e2023096 Conclusions Frontal fibrosing alopecia belongs to the group of inter- face (lichenoid) dermatitis, being characterized histopatho- logically by a perifollicular lymphohistiocytic infiltrate, resulting in fibrosis and scarring [1]. These features make FFA indistinguishable histologically from lichen planopi- laris, of which it is therefore considered a clinical variant [1,2]. To date, only rare cases of FFA associated with oral lichen planus (OLP) have been described [2]. Oral lichen planus is a chronic inflammatory disease also character- ized by interface dermatitis on histopathology. Clinically, it can be distinguished into three main subtypes: reticular, atrophic, and erosive [3]. It has been reported a small but consistent increased risk of oral squamous cell carcinoma development among OLP patients [4]. In OLP, stimulation of cell-mediated immunity leads to activation of cytotoxic CD8+ T lymphocytes directed against cells in the basal layer of the epithelium, with an early increase in Th1-type cyto- kines [3]. Similarly, in FFA the interaction of genetic, hor- monal, and environmental factors would cause the loss of the immune privilege of hair follicles induced by Th1-type inflammation, with up- regulation of the JAK/STAT signaling pathway and pro-fibrotic markers, increased production of IFN-γ, and subsequent activation of CD8+ lymphocytes di- rected against the hair follicle [1,2]. Immune dysregulation seems to be limited to the lesional skin [5]. The coexistence of OLP and FFA in our patient suggests that, although rarely associated, these two disorders could represent two manifestations of the same immune-mediated process. The presence of OLP should therefore be looked for in all patients with FFA by careful clinical inspection of the oral cavity, also taking into consideration the risk of malig- nant progression of oral mucosal lesions. Figure 1. (A) Erosions over an erythematous base, partially covered by whitish pseu- domembranes, located at the level of the vestibule of the mouth and buccal mucosa. (B) Symmetrical eyebrow alopecia accompanied by bilateral fronto-temporal hairline recession. (C) Trichoscopy; loss of visible follicular ostia in the absence of active inflam- matory lesions, yellow dots or vellus hair. (D) Histology; band-like lymphocytic infiltrate in the superficial chorion and at the junction with the overlying mucosa. Research Letter | Dermatol Pract Concept. 2023;13(2):e2023096 3 References 1. 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