Circumscribed palmo-plantar hypokeratosis: a disease of desquamation? Immunohistological study of five cases and literature review

Circumscribed Palmar Hypokeratosis With Superimposed Actinic Keratosis

A man in his late 70s with a history of psoriasis and non-melanoma skin cancer presented with a progressive rash on his right thenar eminence. He first noticed it about one year ago. He denied any pruritus in the affected region but did note some overlying skin breakdown. He had used topical betamethasone and calcipotriene cream in the past with minimal improvement. Physical examination revealed a pink atrophic plaque with linear hyperkeratotic borders and central fissuring on the right thenar eminence extending into the first webspace. A shave biopsy revealed hypokeratosis with a rim of surrounding hyperkeratosis and associated parakeratosis, basal keratinocyte atypia, and lichenoid inflammation. These histopathological features were consistent with circumscribed palmar hypokeratosis and central actinic keratosis. Circumscribed palmar hypokeratosis is often considered a benign entity, but there have been reports suggesting an association with premalignancy. The decision was made to treat with 5-fluorouracil and calcipotriene cream twice daily for six weeks. At his two-month follow-up, he endorsed a robust reaction, which was further suggestive of premalignant change. He had a near-complete resolution of the rash. This case features circumscribed palmar hypokeratosis and suggests a novel treatment option for patients who develop concomitant actinic keratosis.

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.

'Hints' in the horn: diagnostic clues in the stratum corneum

The stratum corneum or horny layer is the uppermost layer of the epidermis, and is mainly responsible for the skin's barrier function. In spite of its complexity at the ultrastructural and molecular level, the features accessible to visualization on conventional histology are relatively limited. Nevertheless, knowledge of subtle clues that one may observe in the stratum corneum can prove useful in a wide range of situations in dermatopathology. We herein review a selection of common and rare entities in which the horny layer may reveal significantly important hints for the diagnosis. These clues include parakeratosis and its different patterns (focal, confluent, alternating, associated with spongiosis, epidermal hyperplasia or lichenoid changes), subcorneal acantholysis, infectious organisms in the stratum corneum (including fungal, bacterial and parasitic), thickening or thinning of the stratum corneum and the presence of different kinds of pigment. Even when normal, the horny layer may prove to be useful when seen in association with severe epidermal damage, a combination of features testifying to the acute nature of the underlying pathological process.

Involvement of Kallikrein-Related Peptidases in Normal and Pathologic Processes

Human kallikrein-related peptidases (KLKs) are a subgroup of serine proteases that participate in proteolytic pathways and control protein levels in normal physiology as well as in several pathological conditions. Their complex network of stimulatory and inhibitory interactions may induce inflammatory and immune responses and contribute to the neoplastic phenotype through the regulation of several cellular processes, such as proliferation, survival, migration, and invasion. This family of proteases, which includes one of the most useful cancer biomarkers, kallikrein-related peptidase 3 or PSA, also has a protective effect against cancer promoting apoptosis or counteracting angiogenesis and cell proliferation. Therefore, they represent attractive therapeutic targets and may have important applications in clinical oncology. Despite being intensively studied, many gaps in our knowledge on several molecular aspects of KLK functions still exist. This review aims to summarize recent data on their involvement in different processes related to health and disease, in particular those directly or indirectly linked to the neoplastic process.

Gene expression profiling in pachyonychia congenita skin

BACKGROUND

Pachyonychia congenita (PC) is a skin disorder resulting from mutations in keratin (K) proteins including K6a, K6b, K16, and K17. One of the major symptoms is painful plantar keratoderma. The pathogenic sequelae resulting from the keratin mutations remain unclear.

OBJECTIVE

To better understand PC pathogenesis.

METHODS

RNA profiling was performed on biopsies taken from PC-involved and uninvolved plantar skin of seven genotyped PC patients (two K6a, one K6b, three K16, and one K17) as well as from control volunteers. Protein profiling was generated from tape-stripping samples.

RESULTS

A comparison of PC-involved skin biopsies to adjacent uninvolved plantar skin identified 112 differentially-expressed mRNAs common to patient groups harboring K6 (i.e., both K6a and K6b) and K16 mutations. Among these mRNAs, 25 encode structural proteins including keratins, small proline-rich and late cornified envelope proteins, 20 are related to metabolism and 16 encode proteases, peptidases, and their inhibitors including kallikrein-related peptidases (KLKs), and serine protease inhibitors (SERPINs). mRNAs were also identified to be differentially expressed only in K6 (81) or K16 (141) patient samples. Furthermore, 13 mRNAs were identified that may be involved in pain including nociception and neuropathy. Protein profiling, comparing three K6a plantar tape-stripping samples to non-PC controls, showed changes in the PC corneocytes similar, but not identical, to the mRNA analysis.

CONCLUSION

Many differentially-expressed genes identified in PC-involved skin encode components critical for skin barrier homeostasis including keratinocyte proliferation, differentiation, cornification, and desquamation. The profiling data provide a foundation for unraveling the pathogenesis of PC and identifying targets for developing effective PC therapeutics.

Circumscribed plantar hypokeratosis responding to topical calcipotriol

BACKGROUND

Circumscribed palmar or plantar hypokeratosis defines a benign condition clinically presented as a well-defined depressed area on the skin. It is characterized by a peculiar histopathological picture with the abrupt thinning of the horny layer of the epidermis.

MAIN OBSERVATIONS

We present a case of a 17-year-old man, who presented with a one-year history of an occasionally painful lesion on his right sole. The diagnosis of circumscribed plantar hypokeratosis was confirmed by histopathology. The lesion was successfully treated with calcipotriol ointment.

CONCLUSIONS

Circumscribed palmar or plantar hypokeratosis is a benign condition that typically affects the hands. Different therapeutic approaches have been unsuccessful. In our patient the lesion was at a less frequent plantar location and the lesion responded to topical calcipotriol.