Unilateral Blaschkoid Lichen Planus.

A 42-years-old male presented with itchy rash which initially appeared over left side of the abdomen and later spread to involve left upper and lower limbs within 4 weeks. On examination, there were violaceous papules and plaques with scaling arranged in inverted S-shape manner over left side of abdomen. [Figure 1] There were linear lesions on left upper limb from axillae to the palm and also on left lower limb from thigh to dorsum of foot. Mucosal surfaces, nails, and scalp were uninvolved. There was no significant past history and there was no drug intake or any local application prior to appearance of lesions. Laboratory investigations including complete blood count, renal and liver function tests were within normal limits. Tests for hepatitis C virus and human immunodeficiency virus were negative.

Figure 1

Violaceous papules and plaques with scaling arranged in inverted S-shaped pattern over left side of abdomen

Histopathological examination showed hyperkeratosis, hypergranulosis, and band-like lymphocytic infiltrate at dermo-epidermal junction confirming diagnosis of lichen planus [Figure 2].

Figure 2

Histopathology showing hyperkeratosis, hypergranulosis, and band of lymphocytic infiltrate at dermo-epidermal junction. (Hematoxyline and Eosine stain X10)

Various morphological patterns of lichen planus (LP) are seen such as hypertrophic, atrophic, linear, actinic, guttate, erosive, follicular and zosteriform.[1] Lines of Blaschko form V shape over upper spine, whorls or S-shape over abdomen and linear shape over Limbs.[1] Blaschkoid LP is idiopathic and a rare entity.[2] Unmasking of abnormal keratinocyte clone is said to be an initiating event for lichen planus.[2] Yayala et al. reported an olanzapine induced Blaschkoid LP.[3] It is a self-limiting disease and generally responds to topical potent steroids and antihistamines.

Blaschkoid and unilateral LP may be misdiagnosed as naevoid psoriasis, inflammatory linear verrucous epidermal nevus (ILVEN), lichen striatus, and contact allergic dermatitis. Lesser pruritus and involvement of other classic sites of psoriasis like scalp and nails and biopsy can differentiate naevoid psoriasis from lichen planus.[4] ILVEN mostly occurs below 5 years of age and generally over legs with intense pruritus. Lichen striatus predominantly occurs in children below 15 years. It is seen as asymptomatic linear papules arranged in form of band with slight scaling and hypopigmentation over proximal part of limbs with spontaneous resolution in 3 to 6 months.[5]

Blaschkoid LP should not be confused with linear LP, since Blaschkoid LP presents in a pattern form such as whorled or “S” pattern along with some linear lesions.[6]

Blaschkoid LP is an uncommon entity. Interestingly our patient had initial lesions that were strikingly Blaschkoid and later on progressed as linear eruption involving only one side of upper and lower extremity. This case is presented here for its rarity and a classic morphological pattern.

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