Dermoscopy: A reliable guide in the diagnosis of lichen planus-like keratosis in an appropriate clinical setting

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A 54-year-old female with skin phototype IV presented with 6 months history of a variable itchy skin lesion over the lower abdomen. Cutaneous examination revealed solitary well-toill-defined skin-colored to reddish-brown plaque (2 cm × 2 cm) with an uneven surface and surface erosion [Figure 1]. Differential diagnoses of sarcoidosis, lupus vulgaris, plaque-type granuloma annulare, and Bowen’s disease were considered. Dermoscopy under non-polarized contact mode showed multiple tiny erosions, homogenous white to gray areas, brown dots (circumscribed, small, and round), blue-gray fine, and coarse peppering (non-circumscribed and not round), and focal clustered glomerular vessels [Figure 2]. After dermoscopic examination, a differential diagnosis of lichen planus-like keratosis (LPLK) was added. Histology revealed orthohyperkeratosis, focal mounds of parakeratosis, hypergranulosis, atrophic epidermis, basal vacuolar degeneration, cytoid bodies, melanophages, and upper perivascular moderate lymphohistiocytic infiltration [Figure 3a and b]. The diagnosis of LPLK was made.

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Figure 1:

Solitary well-to-ill-defined skin-colored to reddish-brown plaque.

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Figure 2:

(a) Dermoscopy (HEINE DELTA20^®, Germany, 10×) under non-polarized contact mode shows multiple erosions, homogenous white to gray areas, brown dots (red asterix), and blue-gray fine (red arrow), and coarse peppering (blue asterix). (b) Dermoscopy shows erosion (blue arrow), brown dots (red asterix), blue-gray coarse peppering (blue asterix), and focal clustered glomerular vessels (circle).

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Figure 3:

(a) Histology shows orthohyperkeratosis, focal mounds of parakeratosis, hypergranulosis, loss of rete ridges, basal vacuolar degeneration, cytoid bodies, melanophages, and upper perivascular moderate lymphohistiocytic infiltration (H&E, ×50). (b) Prominent basal vacuolar degeneration and cytoid bodies (H&E, ×100). (c) Mounds of parakeratosis (blue arrow) and melanin (red arrow, H&E, ×400).

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LPLK, otherwise called benign lichenoid keratosis, is a relatively common benign dermatosis. The original description, in 1966, is because of its histopathological resemblance to LP but without any clinical similarity. It usually skips the diagnosis and is mistaken for another benign and malignant cutaneous neoplasm. In a recent review of 1366 cases of LPLK, only in 5.2% of cases, a differential diagnosis of LPLK was considered, and none of them had a clinical impression of lichen planus. The most common clinical impression was basal cell carcinoma and squamous cell carcinoma. In 8% of the cases, it mimicked a melanocytic lesion, including atypical nevus and melanoma. The majority of the lesions belong to the classic variant (non-pigmented), and other rare variants include atrophic (pigmented), bullous, and mycosis fungoides-like.^[1,2] In contrast to previously reported female preponderance, a recent study found an almost equal prevalence between males and females. The chest is the most commonly affected region, followed by the back and forearm, while the head and neck are not affected. In Asians, the head and neck were the frequent sites of involvement, and the trunk was rarely affected.^[1] A recent study from the West Asian population reported a higher frequency of pigmented LPLK and a lower incidence in females.^[3] A relationship of LPLK with solar lentigo (SL) and reticulated seborrheic keratosis (SK) has been demonstrated.^[4] The differential diagnoses of LPLK, both for pigmented and non-pigmented variants, can be different in dark skin phototypes than in fair-skinned individuals. In contrast to a common presentation, an erythematous papule or plaque, a skin-colored to reddish-brown plaque, was noticed in the index case, leading us to consider mainly granulomatous dermatoses.

The role of dermoscopic examination in diagnosing various cutaneous dermatoses is expanding due to its direct dermoscopic-pathologic correlating properties. Thus, despite the variable clinical morphology, a dermoscopic examination can reflect the histopathological features of the dermatosis. A recent study showed the presence of orange color and scale to be predictive of LPLK. In addition, the presence of coarse peppering and only peppering was the dermoscopic feature for pigmented LPLK.^[5] In the index case, a plaque of non-pigmented LPLK, the observed dermoscopic pattern helped in ruling out other differentials and pointed to the diagnosis of LPLK due to the presence of fine and coarse brown and blue-gray peppering. The blue-gray peppering corresponds to the dermal melanophages and pigment incontinence and brown dots and peppering to increase epidermal pigmentation or melanin in the stratum corneum. In contrast to an orange color, in the index case, we observed homogenous areas of varying color, possibly due to the dark skin color of the patient. The dermoscopic diagnosis of LPLK is relatively easy when associated with an SL or SK, which reflects the intermediate regressing stage.^[6] However, in the absence of clinical or dermoscopic features of SL or SK, the diagnosis of LPLK can be challenging, in which case, a coarse peppering with or without fine peppering can point to the diagnosis of LPLK, as in our case. Dermoscopically, in contrast to LPLK, LP demonstrates Wickham’s striae, diffuse brown area, dotted vessels, and linear capillaries.^[6]

The histopathology of LPLK is similar to that of LP and demonstrates lichenoid infiltrate, basal vacuolar degeneration, apoptotic keratocytes, hyperkeratosis, and hypergranulosis. The presence of focal parakeratosis and RBC extravasation is the discrimination features that are not observed in LP. Besides, in contrast to cutaneous LP, dermal eosinophils, neutrophils, and plasma cells are observed in LPLK. In the index case, mounds of parakeratosis were found in addition to all the classic features of LP, and no associated features of SL or SK were found.^[1,7]

In conclusion, the clinical diagnosis of LPLK is difficult due to the lack of any characteristic clinical morphology, especially in the absence of associated SL or SK. A dermoscopic examination can be a reliable tool in revealing the diagnosis of LPLK in an appropriate clinical setting which can be confirmed by pathological examination.