Naevoid Psoriasis and ILVEN: Same Coin, Two Faces?

The true existence of naevoid psoriasis and inflammatory linear verrucous naevus as distinct entities has been a debatable issue. Each has been opined to be a variant of the other. Considerable clinical and histological resemblance is seen between the two conditions. We describe three cases which attempt to throw more light on this issue.

What was known?

Naevoid psoriasis and ILVEN may not be distinct entities but a variant of each other.

Introduction

The occurrence of psoriasis in a unilateral or linear pattern can give rise to significant diagnostic dilemma. Linear lesions may co-exist with the common chronic plaque form as a result of Koebner phenomenon. But the actual existence of linear psoriasis arising de-novo: the so-called ‘naevoid psoriasis’ has been a debatable issue. Further, there is considerable clinical and histological resemblance between linear psoriasis, inflammatory linear verrucous naevus (ILVEN), lichen striatus, linear lichen planus and invasion of epidermal naevus by psoriasis[1] Exploration of the relation between linear psoriasis and ILVEN has been attempted through clinical, genetic, immunohistochemical and therapeutic studies. We put together the following cases which further illustrates the association between psoriasis and ILVEN.

Case Reports

Case 1

The subject, a five-year-old boy had a moderately itchy skin lesion involving the right side of the body since six months of age. Episodes of remission and exacerbation followed with an improvement in summer. The otherwise healthy child had no similarly involved family member. Multiple erythematous scaly plaques were seen unilaterally on the right side distributed along the C2 and C3 (scalp and neck), C4,5,6,7 and T1,2 (upper limb) and T3,4,5,6,7 (chest) dermatomes [Figure 1]. Auspitz sign was positive. Histology of a typical scaly plaque showed acanthosis, parakeratosis, Munro's microabscess and tortuous dilated capillaries in the dermal papillae. Since the age of the child was not suitable for systemic psoralens, we gave him topical steroids and dithranol as a short contact therapy. The cutaneous lesions cleared within next five months but reappeared again the following winter.

Figure 1

Typical plaques of psoriasis in a naevoid distribution; case one

Case 2

A 12-year-old boy came with a mildly pruritic skin ailment present since infancy. The lesion had started on the left arm and gradually spread to involve the left half of the body and lastly affected both sides of face. Erythematous scaly plaques were seen over left upper and lower limbs (C4-C8 and L2-L5 dermatomes respectively) and back (T8-T12) [Figures 2 and 3]. Auspitz sign was positive on the body lesions but not on the face. The only exception to this strikingly unilateral involvement was the face where the lesions were on both the cheeks [Figure 4]. Skin biopsy from the arm showed typical features of psoriasis including Munro's abscess. With systemic psoralens with ultraviolet A (PUVA) and topical steroids, all except the facial lesions subsided. A second biopsy from the face showed hyperkeratosis, parakeratosis, some spongiosis and an upper dermal lymphohistiocytic infiltrate.

Figure 2

Skin lesions distributed along Blascko's lines on the left side of the body: Case two

Figure 3

typical erythematous scaly plaques of psoriasis on forearm; Case two

Figure 4

Case two: skin lesions on face (right)

Case 3

A five-year-old girl presented with an erythematous linear lesion in the left lower extremity since six months of age. It had gradually become scaly and intensely pruritic. On examination it was found to extend from the posterolateral aspect of the left thigh towards the knee [Figure 5]. No other cutaneous lesion was found. Auspitz sign was negative. Histology showed an irregular epidermal hyperplasia, alternating bands of ortho and parakeratosis, slight spongiosis, absence of granular layer and a dermal inflammatory infiltrate. Munro's microabscess was not seen.

Figure 5

A close-up of skin Lesions in case three

Discussion

The independent existence of linear psoriasis as well as ILVEN has been questioned and each has been opined to be a variant of the other. Some authors feel linear psoriasis is merely an epidermal nevus with psoriasiform features while others feel that ILVEN is nothing but a mosaic form of psoriasis. However segmental manifestation of psoriasis superimposed on a symmetrical involvement has also been documented. To explain this, it has been proposed that loss of heterozygosity occurs in a somatic cell during early embryogenesis which results in either homo-or hemizygosity for one of the genes predisposing to psoriasis. This now is the stem cell of a clone that gives rise to segmental areas of psoriasis.[2]

From clinical and histological aspects, case one had chronic plaque psoriasis not withstanding the fact that the lesions were strikingly linear, unilateral and segmental in distribution and is early in onset. Koebner phenomenon fails to explain the strict unilateral distribution in this case. Moreover the disease changed for the better in summer and there was a favorable response to anti-psoriatic therapy. The occurrence of psoriatic plaques on a pre-existing epidermal nevus has been reported earlier.[3] But in such cases one expects to find psoriatic plaques at other sites as well and biopsy may not show features of psoriasis alone as mentioned earlier, in diseases with a polygenic background such as psoriasis, a linear or segmental pattern is often seen. The linear lesions are earlier to appear than the non-segmental ones and are more difficult to treat. A family member may have the non-segmental form of the disease. But, in our first case, the child had only segmental lesions and no known affected family member. On clearance of the skin lesions, no residual naevus was detected. Though we prefer to stamp the case as isolated naevoid psoriasis, Happle has argued in a similar previously published case that the appearance of non-segmental lesions is a possibility in the later lives of these patients. We are trying to follow up our patient's progress too but that does not in any way invalidate our present diagnosis of naevoid psoriasis in this case.

In 1971, Altman and Mehregan proposed clinical criteria for ILVEN: Early age of onset, 4:1 female preponderance, frequent involvement of left lower extremity, pruritus, distinct and inflammatory linear appearance, following the lines of Blaschko and persistent lesions showing marked refractoriness to treatment.[4] Histological criteria was defined six years later by Dupre and Cristol which stated that in addition to the psoriasiform features, there were distinct alternate bands of hypergranulosis with overlying orthokeratosis and agranulosis with parakeratotic hypergranulosis. case three in our series fulfilled the clinical as well as histological features of ILVEN. In case two, clinically the skin lesions resembled psoriasis, but Auspitz sign was not detectable on the face and biopsy from the facial lesions revealed a distinct histological picture matching ILVEN. While the rest of the lesions subsided with anti-psoriatic therapy, the facial ones remained unchanged. Such a co-existence of bilateral ILVEN and psoriasis has been reported by Oram et al,[5] But our case two shows, along with bilateral facial lesions that matched ILVEN, unilateral dermatomal distribution of skin lesions that clinically and histologically matched the diagnosis psoriasis. This combination is very unusual.

The colocalisation of ILVEN and psoriasis may be explained by the possible proximity of the gene locus for susceptibility to epidermal nevus to one of the major psoriasis genes.[6] Immunohistochemical studies have confirmed that there is increased expression of keratin 10 in ILVEN as compared to psoriasis, while T-cell subsets are markedly reduced. In ILVEN with psoriasis, both T-cell subsets and cells expressing NK receptors are seen in moderate numbers.[7]

The clinical features, histology and therapeutic responses in these cases illustrate ILVEN and nevoid psoriasis as distinct entities which on rare occasions may co-exist in the same subject. We could not perform the genetic and immunohistochemical investigations in our patients for lack of infrastructural support, but mapping of the genes associated with epidermal naevi and of the known psoriasis-associated genes in these patoents might have endowed us with some interesting insights in the genotypical and phenotypical relation between these two entities.

What is new?

ILVEN and nevoid psoriasis are distinct entities which on rare occasions may co-exist in the same subject.