Palmar lichen planus mimicking tinea nigra.

Lichen planus (LP) is a chronic inflammatory skin disease characterized by polygonal, violaceous papules commonly involving flexural areas of the wrists, legs, and oral and genital mucous membranes. This report describes a patient who presented with asymptomatic black colored patches on both palms simulating Tinea nigra, a superficial fungal infection. She was previously diagnosed as allergic contact dermatitis and was being treated with potent topical steroid i.e. clobetasol propionate 0.05% and white soft paraffin. Dermatoscopy of the lesion showed brownish pigmentation along ridges of the dermatoglyphics. A biopsy from the lesional skin showed findings of lichen planus. Our case highlights the potential diagnostic confusion that can occur with unusual variants of palmoplantar lichen planus and importance of histopathology in diagnosis of such unusual lesions.

What was known?

Lichen planus is a common inflammatory papulosquamous disorder. Classically, it is characterized by violaceous polygonal pruritic papules. Localized hyperpigmentation of palms is a rare presentation of lichen planus. Hyperpigmented palmar LP can pose a diagnostic difficulty.

Introduction

Lichen planus is a chronic inflammatory skin eruption chiefly occurring in the middle age, i.e., 30-60 years of life, with no sex or racial differences.[1] Palmoplantar involvement is seen rarely with lichen planus and often does not have the classically morphology, making it difficult to establish the diagnosis.[2] Till date, there is a single case report of palmar lichen planus mimicking superficial fungal infection–tinea nigra.[3]

A 45-year-old healthy housewife presented to our OPD for an opinion on asymptomatic black colored patches present on both palms of two months duration. The lesions had appeared insidiously and were gradually increasing in size. There was no discomfort or itching. She denied any history of contact with any known allergens or drug intake. She also did not give history of any high risk sexual behavior or genital ulcer disease. Cutaneous examination showed a single, well-defined black-colored patch on the right hypothenar surface and three brownish colored patches on the left hypothenar eminence [Figure 1]. Few calluses were noted at the metacarpal head. There was absence of scaling and any surface changes on the lesion. There were no similar lesions on the soles. Rest of the cutaneous, oral, and genital evaluation was within normal limits. We considered a differential diagnosis of tinea nigra, resolved fixed drug eruption, pigmented contact dermatitis, and exogenous pigment. Potassium hydroxide (KOH) mount from the lesions was negative for fungal elements.

Figure 1

Well defined black to brownish colored patches on both the hypothenar eminences of palms

Contact dermatoscopy of pigmented patch showed a hem-like pattern of pigment distribution along the ridges of the dermatoglyphics [Figure 2]. After obtaining informed consent, a biopsy was taken from one of the representative lesion under local anesthesia and was fixed in 10% buffered formalin. A hematoxylin and eosin stained section of skin biopsy showed hyperkeratotic stratum corneum and acanthotic epidermis with vacuolar changes of the basal layer. A band-like infiltrate comprising lymphohistiocytic infiltrate was evident at the dermo-epidermal junction [Figure 3]. Gomori–Methenamine Silver (GMS) stain of skin biopsy did not show presence of fungal hyphae. We prescribed topical clobetasol propionate (0.05%) cream along with white soft paraffin to be applied twice daily. The patient responded completely to the topical steroid cream and emollients [Figure 4].

Figure 2

Dermatoscopy of palmar lesion showing brown colored pigment along the ridges of dermatoglyphics in a hem like pattern

Figure 3

H and E stained section of skin biopsy from the lesion showing hyperkeratotic stratum corneum, vacuolar change of basal layer with interface dermatitis composing of lymphocytic infiltrate abutting the basal layer. (×20)

Figure 4

Same patient six weeks after treatment with topical steroids and white soft paraffin

Palmoplantar lichen planus is a localized and rare variant of lichen planus.[4] Palmoplantar involvement in lichen planus was seen in 26% of their case series in a study done by Sanchez-Peres and colleagues.[5] In contrast to classical lichen planus, lichen planus of palms and soles does not demonstrate Wickham's striae and its typical polygonal lesion.[6] Many clinical variants of palmoplantar lichen planus have been described in the literature. The characteristic morphology of palmar and plantar lichen planus is that of pruritic papules and plaques, which are erythematosus and scaly with well-defined borders. Other clinical variants of palmoplantar lichen planus include pitted plaques,[7] ulcerative lesions,[89] vesicle-like papule,[10] umbilicated papules,[11] punctate keratoderma, perforating palmar lichen planus,[12] and petechiae-like lesions.[13] The differential diagnosis for palmoplantar lichen planus includes verruca vulgaris, psoriasis, callus, punctate palmoplantar keratoderma, arsenical keratosis, papular syphilides, Kyrle disease, acrokeratosis paraneoplastica (Bazex syndrome), punctate porokeratosis, lichen simplex chronicus, and eczematous hand dermatitis.[14]

However, in contrast, our patient had non-itchy and non-palpable macular eruption with well-defined margins. In 2009, Mehta et al. had reported similar palmar pigmentation, which was proved to be lichen planus on histopathology.[3] Aytekin et al. reported hyperkeratotic palmar lichen planus associated with clenched fist, which resolved after topical salicylic acid and methylprednisolone ointment.[15] In our case, we considered a differential diagnosis of tinea nigra and exogenous pigment deposition (argyria). On closer inspection, we were able to notice that each of the patches had dot-like pigmentation involving the ridges more prominently and the same was confirmed with dermatoscopy. Diagnosis of isolated palmoplantar lichen planus is difficult, as it does not present with the classical violaceous papules and lacks Wickham's striae; thus, it can create a diagnostic confusion if other classical features are not evident elsewhere. On clinicopathological correlation, we reached the diagnosis of palmar lichen planus mimicking tinea nigra. The patient was counselled about the benign nature of the condition and was advised to apply topical steroid and emollients. To conclude, we report a case of palmar lichen planus with atypical presentation of localized pigmentation simulating tinea nigra.

What is new?

Lichen planus on the palms can present as well-defined hyperpigmented patches. A high index of clinical suspicion is needed for its diagnosis. Histological examination is must to reach a correct diagnosis. Palmar LP can pose a diagnostic dilemma for a naïve physician.