Double ring sign as a specific dermoscopic feature of lichen planopilaris: Toward a deeper understanding of disease

To the editor, Lichen planopilaris (LPP) is the most common primary cicatricial alopecia defined by the follicular form of lichen planus.1 Histopathologic examination is considered the gold standard diagnostic method. However, it may not always be diagnostically reliable.2 When there is histological ambiguity, trichoscopy is a highly effective tool for diagnosis and monitoring treatment effectiveness.1 Frequently reported trichoscopic findings of LPP include the absence of follicular openings, perifollicular scaling, milkyred areas, and bluegray dots in a target pattern. Perifollicular scaling (casts) is considered the most characteristic trichoscopic feature of LPP and frontal fibrosing alopecia (FFA).3 It varied between 38% and 100% (mean: 85%) of patients with LPP and 42%– 90% (mean: 84%) of patients with FFA.1 Peripilar casts represent hyperkeratosis and lamellar fibrosis resulting from perifollicular lichenoid inflammation, hence, considered ideal sites for biopsy.1,4 Although tubular type of hair casts was considered specific for LPP they were also observed in discoid lupus erythematosus (DLE) and folliculitis decalvance (FD). Contrary to LPP and FFA perifollicular scaling in FD is characterized by a yellowish color.3 However, diagnosis may be challenging in some cases. Considering perifollicular scaling as a frequent and specific dermoscopic feature of active LPP, recognition of its dermoscopic details might help improve the accuracy of clinical diagnosis of LPP and FFA from other diseases causing cicatricialalopecia. Concerning patterns of tubular hair cast, if combined with minimum or absence of interfollicular scales has been described as a specific dermoscopic feature of LPP and FFA by Mathar et al.4 Herein we describe a new dermoscopic pattern of tubular scaling that we detected exclusively in patients with active LPP and FFA lesions. “Double ring sign” consists of two whitesilvery rings of scaling around hair follicle and is identified on dry dermoscopy. The inner ring migrates along the hair shaft and forms a tubular structure that was previously described in the literature.3 The outer ring is a little far from the hair shaft and more delicate than the inner ring (Figure 1A,B). In our experience double ring sign is a helpful dermoscopic finding for differentiating LPP and FFA from other cicatricial alopecia. We evaluated the available dermoscopic images of 102 pathologically confirmed cicatricialalopecia patients with clinically active disease. These include 45 cases of LPP, 36 cases of FFA, 13 cases of DLE, and 8 cases of FD. Double ring sign were observed only in 24 (53.3%) and 13 (36.1%) patients with LPP and FFA, respectively but not in DLE and FD. Among patients with LPP and FFA, those with severe perifollicular scaling (p < 0.001) and positive anagen pull test (p < 0.05) were more likely to have double ring sign (Tables 1 and 2). To correlate dermoscopicpathologic features a 4mm punchbiopsy specimen from the scalp area presenting double ring sign was obtained in three patients after informed consent. The main histopathological findings include lichenoid infiltrates involving infundibulum and isthmus causing reactive infundibular hyperplasia with compact hyperkeratosis extending outward from the follicles (Figure 1C). Regarding presence of whitesilvery scaling in dermoscopy corresponding to parakeratosis in histopathology,5 concentric rings of white scaling in LPP have a parakeratotic nature which is created reactive to perifollicular inflammatory infiltrate.


Double ring sign as a specific dermoscopic feature of lichen planopilaris: Toward a deeper understanding of disease
To the editor, Lichen planopilaris (LPP) is the most common primary cicatricial alopecia defined by the follicular form of lichen planus. 1 Histopathologic examination is considered the gold standard diagnostic method.
However, it may not always be diagnostically reliable. 2 When there is histological ambiguity, trichoscopy is a highly effective tool for diagnosis and monitoring treatment effectiveness. 1 Frequently reported trichoscopic findings of LPP include the absence of follicular openings, perifollicular scaling, milky-red areas, and blue-gray dots in a target pattern. Perifollicular scaling (casts) is considered the most characteristic trichoscopic feature of LPP and frontal fibrosing alopecia (FFA). 3 It varied between 38% and 100% (mean: 85%) of patients with LPP and 42%-90% (mean: 84%) of patients with FFA. 1 Peripilar casts represent hyperkeratosis and lamellar fibrosis resulting from perifollicular lichenoid inflammation, hence, considered ideal sites for biopsy. 1,4 Although tubular type of hair casts was considered specific for LPP they were also observed in discoid lupus erythematosus (DLE) and folliculitis decalvance (FD). Contrary to LPP and FFA perifollicular scaling in FD is characterized by a yellowish color. 3 However, diagnosis may be challenging in some cases. Considering perifollicular scaling as a frequent and specific dermoscopic feature of active LPP, recognition of its dermoscopic details might help improve the accuracy of clinical diagnosis of LPP and FFA from other diseases causing cicatricialalopecia. Concerning patterns of tubular hair cast, if combined with minimum or absence of interfollicular scales has been described as a specific dermoscopic feature of LPP and FFA by Mathar et al. 4 Herein we describe a new dermoscopic pattern of tubular scaling that we detected exclusively in patients with active LPP and FFA lesions.
"Double ring sign" consists of two white-silvery rings of scaling around hair follicle and is identified on dry dermoscopy. The inner ring migrates along the hair shaft and forms a tubular structure that was previously described in the literature. 3 The outer ring is a little far from the hair shaft and more delicate than the inner ring ( Figure 1A In other words, there are alternating circumferential parakeratosis and hyperkeratosis around the hair shaft ( Figure 1C,D).
This indicates that a control mechanism operates to a variable degree in LPP lesions leading to decreased perifollicular infiltration. Therefore, alternation of parakeratosis and orthokeratosis often occurs in lesions that have not been treated. When better understood, it is suggested this mechanism might be utilized in treating or preventing disease.
Probably an intermittent course is an integral part of autoimmune diseases. For instance, alopecia areata presents with Pohl-Pinkus constrictions. 6 We believe along with LPP, in other cicatricial alopecia like DLE or folliculitis decalvance, the same intermittent inflammation may occur. However, we suggest the simultaneous affection of epidermis or interfollicular spaces in such cases mask the dermoscopic feature of hypothetical perifollicular inflammation fluctuation if existing.
In conclusion, double ring sign is a new specific dermoscopic feature of LPP and FFA observed in approximately one-third to half of active lesions. Rings of white-silvery scaling seem to be reactive to "waves" of disease activity related to perifollicular inflammation. It could be easily identified on dry dermoscopy and can benefit clinicians to differentiate LPP and FFA from other causes of cicatricial F I G U R E 1 Double ring sign. Two white-silvery rings of scaling around hair follicles in active lichen planopilaris (A) and frontal fibrosing alopecia (B). Reactive infundibular hyperplasia with compact hyperkeratosis extending outward from the follicles secondary to lichenoid infiltrates involving infundibulum and isthmus of the hair follicle (green arrow). Infundibular hyperkeratosis consists of alternating parakeratosis (red arrows) and orthokeratosis (blue arrow) (H&A, ×40) (C). Schematic histologic image of double rings sign. There is a perifollicular lymphocytic infiltrate leading to reactive infundibular hyperkeratosis. The hyperkeratosis shows alternating circumferential para-and ortho-keratosis around the hair shaft (D).
alopecia. This observation should be validated in future prospective works with a greater sample size.

AUTH O R CO NTR I B UTI O N S
Mina saber involved in research design, project supervision, manuscript writing, and editing. Farahnaz Fatemi Naeini involved in patient recruitment, data collection, and manuscript writing.

ACK N O WLE D G E M ENTS
None.

CO N FLI C T O F I NTER E S T S TATEM ENT
The authors have no conflict of interest to declare.

DATA AVA I L A B I L I T Y S TAT E M E N T
The data supporting the findings of this study are available from the corresponding author upon reasonable request.

E TH I C A L A PPROVA L
This study has been approved by the ethics committee of the Isfahan University of Medical Sciences.

I N FO R M ED CO N S ENT
Informed consent for the publication of medical images was obtained from the patients.