Lichenoid Keratosis: A Clinical Trap without Secrets for Reflectance Confocal Microscopy

Lichenoid keratosis (LK), also known as benign LK, lichen planus-like keratosis (LPLK), or involuting lichenoid plaque, was first described in 1966 as a solitary form of lichen planus. It was later reclassified as LPLK by Shapiro and Ackerman [1]. Clinical and dermoscopic features of LK can vary, often not providing useful and necessary indications to perform an accurate diagnosis without performing a biopsy or histological examination. Here, we describe 2 cases of LPLKs evaluated by means of dermoscopy and reflectance confocal microscopy (RCM).

A 65-year-old woman, without family history of skin cancer, presented with ta pink-violet solitary lesion on the leg of 2 years’ duration (Fig. 1a). The lesion encrusted sporadically. On dermoscopy, it displayed a nonspecific pattern of benign or malignant skin tumors. It showed the presence of multiple polymorphous vascular patterns (linear, looped, and coiled vessels) distributed in the entire lesion as well as white and orange dots and clods (Fig. 1b). Examination by RCM revealed a typical honeycombing pattern at both the spinous and granular layers of the epidermis, with several round-oval dark structures consistent with comedo-like openings, and the presence of elongated cords corresponding to acanthotic (hyperplastic) epidermis bulging against the packed papillae (Fig. 1c). RCM also showed an inflammatory infiltrate at the dermo-epidermal junction closer to bulging packed papillae (Fig. 1d). Two RCM blocks illustrated the presence of inflammatory cells and melanophages. These features strongly suggested a diagnosis of inflamed or regressive benign keratotic lesion. Histopathologic examination confirmed the diagnosis of LPLK (Fig. 1e).

The second lesion was reported in a 45-year-old man. Dermoscopy revealed a polymorphic vascular pattern on a soft pink background and some light brown areas in the borders that could not be traced back to a real pigment network (Fig. 2a). These features were nonspecific and did not lead to a clinical diagnosis of benign or malignant lesion with certainty. We performed RCM showing the presence of a typical honeycombing pattern related to several round oval dark and hyper reflective oval structure, attributable to comedo-like openings (Fig. 2b). Moreover, an RCM mosaic performed at a deeper level revealed the presence of elongated cords, bulbous projections and, within the interpapillary spaces, several bright round cells, brisk inflammatory cells (Fig. 2c).

Dermoscopic analysis does not support a reliable diagnosis in these cases because of the absence of specific criteria consistent with a melanocytic lesion. A previous stepwise RCM approach for solitary pink lesions by Gill and Gonzalez [2] has facilitated appropriate diagnosis. Following RCM examination, surgical excision of the lesions for histopathologic analysis confirms the RCM diagnosis of LK. To our knowledge, there is only one case described by Nagrani et al. [3] reporting the usefulness of RCM to detect an unclear case of LPLK. Due to this difficulty, wrong diagnosis of LK is very frequent [4]. Zaballos et al. [5] reported 24 cases of the dermoscopic pattern of intermediate stage in seborrheic keratosis regressing to LK, suggesting the presence in 63% of BCC, in 24% squamous cell carcinoma, in 6% seborrheic keratosis, and in 1% miscellaneous. In our cases, dermoscopy did not reveal peripheral gray pigment or other element strictly related to LPLK diagnosis, but only the presence of a polymorphic vascular pattern and some white-brown dots and clods. Nagrani et al. [3] reported the usefulness of RCM and dermoscopy in the diagnosis of difficult to detect LPLK, discussing the different stages of regression, which result in different appearances. Only few data are published on RCM pitfalls of difficult to detect LPLKs, confirming similar RCM aspects to our experience. In particular, typical honeycombing pattern related to several round oval dark and hyperreflective oval structures, attributable to comedo-like openings. Moreover, there were some bright round cells consistent with inflammation, located in the interpapillary spaces, and numerous bright-stellate spots or plump bright cells in the superficial dermis. Ramirez-Fort et al. [4] also reported the absence of discernible papillae consistent with an epidermal neoplasm (i.e., seborrheic keratosis), blunting the regular contour of the dermo-epidermal junction and allowing correct diagnosis [3, 4].

In conclusion, RCM is a useful tool to diagnose difficult cases of LK, revealing features invisible to dermoscopic approaches.

Subjects have given their informed consent to publish their case (including publication of images), and the study protocol has been approved by the institute’s committee on human research.

The authors do not report any conflicts of interest related to this work.

None.

Dr. S.M., T.C., C.L., M.D.P., V.V., and Prof. E.C., S.G., L.B. contributed to conception or design of the work; or the acquisition, analysis, or interpretation of data for the work; AND drafting the work or revising it critically for important intellectual content; AND final approval of the version to be published; AND agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.