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Circumscribed palmar or plantar hypokeratosis (CPH) was first reported in 2002 by Perez et al.,1 who described the largest case series (to date) involving 10 patients with a characteristic epidermal malformation of the palms and soles. They considered CPH to be a benign clonal epidermal malformation.

Here, we report two cases of CPH, both occurring in elderly Japanese women. The first patient, aged 79 years, presented with a single, well-defined, depressed skin lesion on the thenar aspect of the left palm. Physical examination revealed a slightly depressed area of erythema measuring 22 mm × 14 mm (Fig. 1a). The second patient, aged 73 years, presented with a well-circumscribed, solitary, depressed area of erythematous skin and slightly depressed area of erythema measuring 8 mm × 7 mm (Fig. 1c). Both lesions had increased in size over the course of a few years, but had been present for 10–20 years without any history of trauma or possible contributory incident. Treatment with topical corticosteroids had been ineffective. Histologically, both lesions showed a well-demarcated, abrupt decrease in the thickness of the stratum corneum with a central area of thinning and hypogranulosis; inflammation was absent in the upper dermis. The borderline of the lesion between the areas of the thick and thin horny layer was somewhat shaggy, but relatively well demarcated (Fig. 1b,d). The epidermis did not show Bowen’s disease-type atypical keratinocytes, palmar porokeratosis-like cornoid lamellation, lipid deposition or disorganization of the epidermal layer. Immunohistochemical examination demonstrated overexpression of AE1 + AE3, and decreased expression of K9 and K2e (Fig. 1e–g). Expression of K16 and Ki-67 showed no marked difference between normal skin and lesional skin (data not shown). Body site-specific differentiation of keratinocytes, including interfollicular (represented by K1–K10 expression) and palmoplantar (K1–K9) keratinocytes, mucosal (K4–K13) or even corneal (K3–K12) epithelial cells, is now believed to result from soluble factors secreted by the underlying fibroblasts.2

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Figure 1.  Clinical and histological features. (a) Case 1. A slightly depressed area of erythema measuring 22 mm × 14 mm on the thenar aspect of the left palm of a 79-year-old woman. (b) Histology of case 1 demonstrates a thick horny layer demarcated by a depressed, thin horny layer (hematoxylin–eosin [HE], original magnification ×100). (c) Case 2. A slightly depressed area of erythema measuring 8 mm × 7 mm on the right thenar eminence of a 73-year-old woman. (d) Depression of the epidermis with a thin horny layer in case 2 (HE, ×100). (e) Anti-pankeratin AE1 + AE3 shows strongly positive staining in the lesional suprabasal keratinocytes (case 1, original magnification ×100). (f) K9 expression is decreased in the affected epidermis (case 1, ×100). (g) Cytokeratin 2e expression is decreased in the lesion (case 1, ×100).

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To date, 35 cases have been reported in the English published work, and their clinical characteristics are summarized in Table 1. Characteristically, the ages of the patients ranged 35–81 years (mean 64.0 years). CHP occurs mainly in middle-aged or elderly women, with a predilection for the thenar palm. Only three of the reported cases of CPH developed on the sole, and the other 36 cases affected the palm. Twenty-three lesions occurred on the thenar eminence, eight on the hypothenar eminence, one case on the palmar aspect of the index finger and ring finger, and two cases on the thumb. Four cases involved multiple lesions. The duration of the lesions, when noted, ranged 2–40 years. All except one of the reported CPH cases were manifested clinically as an erythematous lesion. Several hypothetical pathogeneses have been proposed, such as a primary keratinizing disorder of the granular and horny layers, trauma, human papilloma virus type 4 infection, or clonal epidermal malformation. The most common clinical differential diagnosis at presentation was Bowen’s disease. In an immunohistochemical study of CPH, Ishiko et al.3 reported that overexpression of anti-pankeratin antibody (AE1 + AE3) and K16, and decreased expression of K2e were evident in the lesional skin. In addition, Tanioka et al.4 noted complete disappearance of the expression of palm- and sole-specific K9 in the hypokeratotic lesional epidermis.

Table 1.   Summary of 35 cases previously reported in the English published work (including our cases)
Female/male26/9
Age (years) of onset (mean)35–81 (64.0)
Duration in years, number of cases
 0–1017
 11–204
 21–305
 >307
 Not stated2
Number of lesions, number of cases
 Solitary31
 Multiple (two lesions in each case)4
Location, number of lesions
 Right hand21
 Left hand15
 Thenar23
 Hypothenar8
 Thumb2
 Palm1
 Ring finger1
 Index finger1
 Plantar3
Etiological factorsClonal epidermal proliferation
Trauma
Human papilloma virus type 4
Loss of keratinocytes

Although published reports of CPH have been increasing recently, its pathogenesis is still unclear. The diagnosis of CPH is based on its clinical manifestation, anatomical site and immunohistochemical characteristics (loss of K9 and K2e and overexpression of AE1 + AE3). The presented two cases demonstrated no changes of proliferative epidermal tumor or cornoid lamella, however, the CPH lesions must be distinguished clinically from Bowen’s disease, arsenic keratosis or palmoplantar porokeratosis.

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