Circumscribed palmo-plantar hypokeratosis: a disease with two subtypes

Circumscribed palmoplantar hypokeratosis

Circumscribed palmoplantar hypokeratosis (CPH) is a rare acquired dermatosis first described in 2002. It affects mostly the thenar or hypothenar eminences of the palm of middle-aged or elderly women and manifests clinically with sharply limited, annular erythematous plaques with a depressed surface, rimmed by a slightly raised, keratotic border. Microscopically, circumscribed palmoplantar hypokeratosis shows a sharp decrease of the horny layer thickness, with few, if any, associated changes (parakeratosis, dermal inflammation). Despite a characteristic clinical and microscopic aspect, the disease remains poorly known, as does its pathogenesis, even if several hypotheses have been proposed (clonal epidermal malformation, disorder of epidermal differentiation/keratinization and/or desquamation, human papillomavirus- or trauma-induced disease). Several therapies have been proposed with varying results, the best ones achieved with surgical excision; however, because the disease is benign, intervention is optional. © 2020 Elsevier Inc. All rights reserved.

Hyperkeratotic hand eczema: Eczema or not?

Background

Hyperkeratotic hand eczema (HHE) is a typical clinical hand eczema subtype with a largely unknown pathophysiology.

Objective

To investigate histopathology, expression of keratins (K), epidermal barrier proteins, and adhesion molecules in HHE.

Methods

Palmar skin biopsies (lesional and perilesional) were obtained from seven HHE patients and two healthy controls. Moreover, 135 candidate genes associated with palmoplantar keratoderma were screened for mutations.

Results

Immunofluorescence staining showed a significant reduction of K9 and K14 in lesional skin. Upregulation was found for K5, K6, K16, and K17 in lesional skin compared with perilesional and healthy palmar skin. Further, upregulation of involucrin and alternating loricrin staining, both in an extracellular staining pattern, was found. Filaggrin expression was similar in lesional, perilesional, and control skin. No monogenetic mutations were found.

Conclusion

Currently, the phenotype of HHE is included in the hand eczema classification system; however, it can be argued whether this is justified. The evident expression of filaggrin and involucrin in lesional skin does not support a pathogenesis of atopic eczema. The upregulation of K6, K16, and K17 and reduction of K9 and K14 might contribute to the underlying pathogenesis. Unfortunately, comparison with hand eczema studies is not possible yet, because similar protein expression studies are lacking.

Circumscribed palmoplantar hypokeratosis: report of two Brazilian cases

Circumscribed palmoplantar hypokeratosis is a recently recognized dermatosis and rarely reported. It was first described in 2002 and is characterized by localized loss of the horny layer in the palmoplantar area. This dermatosis is clinically presented with a sharply circumscribed, reddish and asymptomatic plaque with slightly depressed surface localized on the palms or the soles. The clinical differential diagnosis includes mainly porokeratosis and Bowen's disease. Its pathogenesis remains unknown, but studies have proposed a human papillomavirus induced disease or a localized keratinization disorder in the palmoplantar area. We report herein two cases of patients with lesions clinically and microscopically compatible with the diagnosis of circumscribed palmoplantar hypokeratosis. We also present a brief literature review of the etiopathogenic hyphoteses of this dermatosis.

A congenital case of circumscribed acral hypokeratosis

Circumscribed acral hypokeratosis is a disorder characterized by areas of erythematous depressed skin with distinct histopathological findings typically found on the palmar and plantar surfaces. Most patients are middle-aged women who report a multiyear history. We present an 10-year-old African American boy who had an asymptomatic, irregularly shaped erythematous lesion on his left medial foot that had been present since birth. A biopsy showed an abrupt, well-demarcated decrease in the thickness of the stratum corneum layer, with no parakeratosis, that was consistent with a diagnosis of circumscribed hypokeratosis. This represents the first pediatric and congenital case of circumscribed hypokeratosis reported. We review the literature and discuss the ramifications of a congenital case on understanding the etiology of circumscribed hypokeratosis.

Circumscribed palmar hypokeratosis: Successful treatment with fluorouracil cream

Introduction

The pathogenesis of circumscribed palmar hypokeratosis (CPH) is still controversial, and to date there is no treatment of choice.

Methods

We report on a patient with CPH responding to treatment with fluorouracil cream.

Results

The clinical course and histopathological features in our observation point towards the possibility of an underlying squamous cell carcinoma in situ presenting as CPH.

Conclusion

We suggest that fluorouracil cream treatment should be considered as a therapeutic option in cases of CPH.

The p63 target HBP1 is required for skin differentiation and stratification

Genetic experiments established that p63 is crucial for the development and maintenance of pluristratified epithelia. In the RNA interference (RNAi) screening for targets of p63 in keratinocytes, we identified the transcription factor, High Mobility Group (HMG) box protein 1 (HBP1). HBP1 is an HMG-containing repressor transiently induced during differentiation of several cell lineages. We investigated the relationship between the two factors: using RNAi, overexpression, chromatin immunoprecipitations and transient transfections with reporter constructs, we established that HBP1 is directly repressed by p63. This was further confirmed in vivo by evaluating expression in p63 knockout mice and in transgenics expressing p63 in basal keratinocytes. Consistent with these findings, expression of HBP1 increases upon differentiation of primary keratinocytes and HaCaT cells in culture, and it is higher in the upper layers of human skin. Inactivation of HBP1 by RNAi prevents differentiation of keratinocytes and stratification of organotypic skin cultures. Finally, we analyzed the keratinocyte transcriptomes after HBP1 RNAi; in addition to repression of growth-promoting genes, unexpected activation of differentiation genes was uncovered, coexisting with repression of other genes involved in epithelial cornification. Our data indicate that suppression of HBP1 is part of the growth-promoting strategy of p63 in the lower layers of epidermis and that HBP1 temporally coordinates expression of genes involved in stratification, leading to the formation of the skin barrier.