Circumscribed palmar or plantar hypokeratosis: report of an italian case.

Circumscribed palmar or plantar hypokeratosis is a rare benign epidermal malformation of the skin. Clinically it shows asymptomatic, well-circumscribed, and depressed erythema persisting for many years on the palms or soles. Its main histopathologic feature shows a characteristic epidermal depression with an abrupt decrement in the thickness of the stratum corneum, with a sharp stair between normal and involved skin. We describe a case of a 68-year-old woman who presented with an erythematous, asymptomatic, well-circumscribed, depressed patch, on the right thenar eminence which had been present for years.

Introduction

Circumscribed palmo-plantar hypokeratosis (CPH) is a rare dermatosis, first described by Perez et al. in 2002.[1] Only about 50 cases have been described in the literature so far, of which two were with a unique plantar localization.[2] The disorder usually affects women (with a female:male ratio of 4:1), with a mean age of presentation of 61 years. The pathogenesis of this disorder is unclear. It presents clinically with annular erythematous depressed patch rimmed by a slightly hyperkeratotic border; the lesion is usually unique and localized over the thenar or hypothenar eminence of the palms, rarely on the soles. CPH presents clinical stereotypical features even if sometimes it is misdiagnosed as palmar porokeratosis or Bowen's disease. Its main histopathologic feature shows a characteristic epidermal depression with an abrupt decrement in the thickness of the stratum corneum, with a sharp stair

Case Report

A 68-year-old woman presented with an acquired, asymptomatic, slowly enlarging erythematous patch on the thenar eminence of her right hand. The patient did not have a history of any local trauma or infectious disease. Her medical history included a mammary adeno-carcinoma treated with surgery and radio-therapy 10 years before. Examination revealed over the right eminence thenar an approximately 15 × 10 mm, well-circumscribed circular erythematous area, depressed, with sharp step between involved and uninvolved skin [Figure 1]. The lesion was unique, without any lesion on the soles of the feet. A full clinical examination was otherwise non-significant. We performed a mycologic examination, which showed normal results. A 4-mm punch biopsy was taken through the edge of the lesion. Histopathology showed a sharply demarcated depressed area with markedly thinned stratum corneum with normal basal layers. The stratum corneum was orthokeratotic and no parakeratois was seen. Slight dilatation of the dermal superficial vessels was noted, with poor lymphocytic infiltration and edema. There was no evidence of cornoid lamella excluding a diagnosis of porokeratosis. Corneocytes of the upper layers showed signs of vacuolization and they became eosinophilic at the edge [Figure 2]. Based on these findings, the diagnosis of circumscribed palmar hypokeratosis was established. Immunohistochemistry was negative for human papilloma virus (HPV). Topical treatment with corticosteroid was of no benefit. The patient is currently on clinical follow-up and in 7 years there has been no evidence of enlargement or evolution.

Figure 1

A circular and well-circumscribed area of depressed and erythematous skin on the right thenar eminence

Figure 2

Skin biopsy specimen from border of the lesion: sharp step-off from the thick stratum corneum of normal acral skin to the thin stratum corneum of the involved skin (hematoxylin–eosin staining; original magnification ×200)

Discussion

CPH is a benign dermatosis of unknown origin predominantly seen in adult women (female:male ratio 4:1; mean age 61 years). Perez et al. argued that it is a localized acquired epidermal malformation because of the presence of the lesions for many years and the absence of a trauma at the site of the lesions.[1] Urbina et al., using transmission electron microscopy, showed a reduction in keratin bundles and keratohyaline granules, and increased lipid in the horny layer, suggesting a primary disorder of keratinization.[3] In contrast to these studies, Resnik et al. suggested that circumscribed palmar or plantar hypokeratosis represents a localized defect in the maturation of keratin, which could follow subclinical episodes of trauma.[4] In our case immunohistochemistry gave a negative result for HPV. However, HPV type 4 has been demonstrated in a recent case. Interestingly, in this case the lesion had been present for an unusual short time of 6 months.[5] CPH is chronic dermatosis with a benign evolution; the lesions slowly progress or remain stable over years as in our case. Only in one recently reported case malignant transformation has been described.[6] The lesions typically involve the thenar and hypothenar eminences of the palm or the medial side of the sole. Clinically they appear as circular and well-circumscribed areas of depressed and erythematous skin with slightly elevated scaly borders. In most cases, the lesions are asymptomatic and there in no evidence of a local trauma. CPH should be clinically differentiated from porokeratosis of Mibelli and Bowen's disease. Histopathologic features are characteristic and they consist of a localized depression of the epidermis, with a sharp stair between normal and involved skin. The stratum corneum is thinner and orthokeratotic, with a stratum granulosum slightly decreased compared to the adjacent non-involved skin. No parakeratosis, atypical keratinocytes or cornoid lamella are generally evident. The underlying dermis also appears normal without a specific inflammatory infiltration. For accurate diagnosis, a biopsy should be performed at the border's lesion to compare the horny layer of the involved skin with that of the non-involved adjacent skin. In literature, various topical treatments are proposed, including corticosteroids, salicylic acid and retinoids, but they all have been disappointing. Urbina et al. reported resolution in one case after 4 years of topical therapy with calcipotriol.[3] Boffa and De Gaetano reported a case of resolution after treatment with liquid nitrogen cryotherapy.[7] Benoit et al. reported a case of partial remission by photodynamic therapy.[8] There are also a few reports of spontaneous resolution.[4] In our patient, no improvement was evident after treatment with a topical steroid for 3 months. In summary, we have described here an additional case of circumscribed acral hypokeratosis. As has been described in literature, we did not find evidence of trauma as an inciting factor in our case. Unlike another reported case, we did not identify evidence of HPV within lesions by immunohistochemistry. We consider this disorder as an acquired non-inflammatory defect in keratinization on acral sites with a remote potential of malignant transformation; for this reason, we consider a prolonged clinical follow-up essential, as in our case.