Psoriasiform keratosis

ARTICLE

Auteur(s) : Angelo Carbone¹, Clara De Simone¹, Francesco Valenzano¹, Pierluigi Amerio¹, Guido Massi²

¹Department of Dermatology, Catholic University of the Sacred Heart, Rome, Italy
²Department of Pathology, Catholic University of the Sacred Heart, Rome, Italy

Psoriasiform keratosis is a new clinical entity characterised by a usually solitary lesion whose histological features closely mimic psoriasis [1, 2]. Scant data are available on this entity. We describe a case of psoriasiform keratosis, its clinical and histopathological characteristics and its surgical excision as a possible management option.

In December 2006, a 25-year-old Caucasian man was seen for a reddish, hyperkeratotic patch 2 cm in diameter that had arisen on his left calf four months earlier. Auspitz’s sign was negative (figure 1A). The lesion had grown slowly despite topical treatment with steroid cream for one month, prescribed by his GP. Past medical history was negative for skin diseases; no signs of other dermatoses were noted at presentation. Lack of response to topical steroids and absence of scalp dermatitis, nail changes and/or other suggestive skin lesions excluded psoriasis and eczema. Family history, including the parents and one brother, was negative for psoriasis. Dermoscopy showed a vascular pattern characterised by glomerular vessels, each surrounded by a whitish hyperkeratotic halo (figure 1B), which are more common in Bowen’s disease than in psoriasis (60% vs 12%) [3]. A diagnosis of Bowen’s disease was established and an incisional biopsy performed. In the histopathology several features were consistent with psoriasis (figure 2), including symmetrical epidermal hyperplasia with elongated, thinned rete ridges; a thickened spinous layer with focal suprapapillary plate thinning; focal absence of granular layer (corresponding to parakeratotic areas in the horny layer); and a thickened stratum corneum with parakeratosis and orthokeratosis. Several neutrophils were seen in the parakeratotic foci, often in alternating tiers among parakeratotic scales. Munro microabscesses and Kogoj’s spongiform pustules were abundant. Tortuous dilated vessels were found in elongated thinned papillae in the dermis. A PAS stain for fungi was negative. A diagnosis of psoriasis was made.

Daily application of clobetasol propionate ointment for six weeks slightly reduced erythema and scaling, but failed to induce lesion regression. The lesion was excised. The histological features were again consistent with psoriasis. Comparison of Ki67 immunohistochemistry findings to three previous cases of psoriasis showed high basal layer expression of Ki67 in all cases, without significant differences between the current single lesion and the previous cases. At one year the lesion has not relapsed and the patient is free of any skin manifestations of psoriasis.

This appears to be the youngest reported case of psoriasiform keratosis as defined by Walsh et al. [1], i.e., a usually unilesional patch clinically suggesting psoriasis, eczema, actinic keratosis, basal cell carcinoma or Bowen’s disease, with a histological pattern consonant with psoriasis arising in patients without any other manifestation or a family history of psoriasis.

The clinical course of this lesion and the ineffectiveness of topical steroids indicate that psoriasiform keratosis may be an epithelial proliferation sui generis having the histological features of but no relation to psoriasis. The condition is reminiscent of other cutaneous diseases morphologically simulating, but unrelated to, specific cutaneous inflammatory diseases. Porokeratoma [4] is a solitary tumour-like lesion with prominent cornoid lamellae closely mimicking Mibelli’s porokeratosis but arising in patients with no other sign of porokeratotic disease; epidermolytic acanthoma [5] involves solitary or disseminated lesions whose histological features are indistinguishable from bullous congenital ichthyosiform erythroderma. The keratosis most closely simulating widespread dermatosis is lichenoid keratosis (lichen planus-like keratosis), which sometimes is undistinguishable from true lichen planus [6]. Such entities are neoplastic or hyperplastic processes accompanied by a peculiar inflammatory reaction pattern triggered by unknown causes. The few available data on psoriasiform keratosis may partly be ascribed to misdiagnosis. Given its proclivity not to regress spontaneously and the ineffectiveness of anti-inflammatory therapy, other approaches, like surgical excision or physical treatment should be considered.

In conclusion, from a practical point of view, when a solitary erythematous patch with the histological features of psoriasis arises in non-psoriatic patients and is refractory to steroids, a diagnosis of psoriasiform keratosis should be considered.

Acknowledgements

References

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3 Pan Y, Chamberlain AJ, Bailey M, Chong AH, Haskett M, Kelly JW. Dermatoscopy aids in the diagnosis of the solitary red scaly patch or plaque-features distinguishing superficial basal cell carcinoma, intraepidermal carcinoma, and psoriasis. J Am Acad Dermatol 2008; 59: 268-74.

4 Walsh SN, Hurt MA, Santa Cruz DJ. Porokeratoma. Am J Surg Pathol 2007; 31: 1897-901.

5 Knipper JE, Hud JA, Cockerell CJ. Disseminated epidermolytic acanthoma. Am J Dermatopathol 1993; 15: 70-2.

6 Morgan MB, Stevens GL, Switlyk S. Benign lichenoid keratosis: a clinical and pathologic reappraisal of 1040 cases. Am J Dermatopathol 2005; 27: 387-92.