A Case of Psoriasis Encircled by Porokeratosis.

Sir,

Porokeratosis (PK) is a heterogeneous group of epidermal keratinization disorders characterized by annular plaques with an atrophic center surrounded by a raised, scaly keratotic wall. It can be inherited or acquired (sporadic), the latter most commonly attributed to immunosuppression.[1] Several clinical variants have been reported, namely, plaque type (classic PK of Mibelli), disseminated superficial (actinic), giant, palmoplantar (Mantoux), linear, and punctate.[2] Psoriasis vulgaris is a chronic, recurrent, disfiguring, inflammatory, and proliferative disorder of the skin characterized by the formation of well-circumscribed erythematous plaques, with micaceous scaling developing in genetically predisposed individuals.[3] Both the disorders have characteristic histological features: PK characterized by cornoid lamella and psoriasis showing hyperkeratosis with elongated club-shaped rete ridges. Seldom, PK of Mibelli may clinically resemble psoriasis vulgaris when they are distinguished by their typical histopathological picture. However, if a patient refuses biopsy because of its invasive nature, we may use dermoscopy (a noninvasive technique) to delineate these disorders.[4] Here, we report a case where a single lesion showed the clinical and histopathological features of both these disorders.

A 42-year-old female presented to us with a single, scaly, itchy, and elevated skin lesion on the posterior aspect of her left ankle. The lesion had been present for the last 16 years. Initially, there was a single, itchy, swollen lesion with micaceous scales which progressively increased in size over the years. She also complained of occasional pain. Her medical and family histories were unremarkable. She had a history of prolonged application of potent topical corticosteroids, without appreciable benefit. Her general health was satisfactory. Cutaneous examination revealed a single, well-circumscribed, roughly circular erythematous plaque, measuring about 8 cm × 6 cm, located over the posterior aspect of her left ankle [Figure 1]. The surface of the lesion had lamellated, easily detachable mica-like scales. The edge of the lesion was slightly raised compared to the central part and had a barely visible central groove indicative of a clinical diagnosis of PK of Mibelli. Hair, nail, and mucosa were spared. Rest of the systems were within normal limits. Her routine blood investigations were unremarkable. Punch biopsy sample from the edge of the lesion showed on histopathology a prominent cornoid lamella. Hypogranulosis and vacuolated basal layer were observed beneath the cornoid lamella consistent with the diagnosis of PK [Figures 2 and 3]. However, biopsy from the center of the lesion showed parakeratotic hyperkeratosis and hypogranulosis along with regular acanthosis with elongated, club-shaped rete ridges, and thinning of the suprapapillary plate pointing toward a diagnosis of psoriasis vulgaris. We prescribed a combination of emollients, topical keratolytics (salicylic acid 6%), topical corticosteroids, and topical retinoic acid (0.05%) and advised follow-up after 2 months.

Figure 1

Psoriasiform plaque with ridged border

Figure 2

Biopsy from ridge showing cornoid lamella, underlying hypogranulosis consistent with porokeratosis (H and E, ×100), inset showing magnified cornoid lamella (H and E, ×400)

Figure 3

Center of the lesion showing parakeratotic hyperkeratosis, and club-shaped rete ridges consistent with psoriasis (H and E, ×100)

PK may rarely occur in association with psoriasis. Hivnor et al.[5] recently demonstrated similar gene expression in the cornoid lamella of PK and psoriasis resulting in similarities in the messenger RNA of hyperproliferating keratins, certain gap junction proteins (connexin26 and 30), and specific members of the S-100 calcium-binding proteins in these two different disorders. Recently, the patients presenting with both these disorders have been classified into three groups by Yazkan et al.;[6] the first group has lesions of PK mimicking psoriatic lesions (e.g., verrucous porokeratotic plaques), the second group includes patients of PK who also have plaque psoriasis, while the third group consists of psoriatic patients developing lesions of disseminated superficial actinic PK (DSAP) as a result of therapeutic phototherapy.[7] Our patient presented with a single lesion of PK (Mibelli) which mimicked psoriasis vulgaris. There was no evidence of any other psoriatic plaque or DSAP in our patient.

The most remarkable feature of our case was the coexistence of histological features of two different disorders (PK and psoriasis) in the same lesion. The elevated edge corresponded to the histological finding of cornoid lamella (PK) while it surrounded an area with psoriasiform features; this picture has been described as “psoriasis encircled by PK.”[6] This kind of histological change has been reported very rarely in English literature. De Simone et al.[8] reported a single case of giant verrucous PK with psoriatic histologic features in the same lesion. However, our case had a plaque with central psoriasiform clinical features surrounded by a ridge that was characteristic of PK of Mibelli. Thus, there was a mixture of both clinical and histological features of the two distinct disorders of keratinization in a single lesion.

Several cases of PK have been reported to develop following systemic and local immunosuppression due to organ transplantation, hematopoietic malignancies, HIV infection, use of immunosuppressive drugs, and ultraviolet light-induced local immunosuppression.[8] Prolonged application of topical corticosteroids may also lead to the development of PK.[6] In our case also, PK of Mibelli probably developed over preexisting plaque of psoriasis vulgaris, following prolonged application of potent topical corticosteroid. Another possibility of psoriasis developing at the center due to the centrifugal spread of PK (Koebner phenomenon) may also be considered. However, there is no evidence of Koebner phenomenon in our patient and the primary lesion appears to be that of psoriasis (patient's history and previous medical documents) over which PK developed as a secondary phenomenon.

Several therapies have been tried for localized PK including surgical resection, cryotherapy, electrocautery, CO2 laser ablation, and topical medications such as retinoids, tacalcitol, keratolytics, 5-fluorouracil, corticosteroids, and imiquimod.[2] Oral retinoids (etretinate) have been tried in persistent and widespread lesions.[28]

Thus, our patient presented with a psoriasiform plaque surrounded by a ridged border resembling that of PK (Mibelli) which showed combined histological features of PK at the periphery and psoriasis at the center. This type of combined histological presentation has not yet been reported in PK of Mibelli. Incidentally, a biopsy from the center would have failed to diagnose the condition showing only psoriasiform features consistent with psoriasis, a benign condition. On the other hand, PK of Mibelli is a precancerous condition which demands specific therapy. Hence, in such lesions, biopsy should be preferably done from the edge for accurate diagnosis and proper treatment.

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