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Related Concept Videos

Cells of the Epidermis01:24

Cells of the Epidermis

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The epidermis is made of four or five layers of epithelial cells, depending on its location in the body. From deep to superficial, these layers are the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum.
The cells in all these layers except the stratum basale are called keratinocytes, a type of cell that manufactures and stores the protein keratin. The keratinocytes in the stratum corneum are dead and regularly slough away, being replaced by cells from...
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Papillary Dermis01:11

Papillary Dermis

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Dermis
The dermis might be considered the "core" of the integumentary system, as distinct from the epidermis and hypodermis. It contains blood and lymph vessels, nerves, and other structures, such as hair follicles and sweat glands. The dermis is made of two layers of connective tissue that comprise an interconnected mesh of elastin and collagenous fibers, produced by fibroblasts.
Papillary Layer
The papillary layer is made of loose, areolar connective tissue, which means the collagen...
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Skin Cancer01:30

Skin Cancer

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Skin cancer is a type of cancer that occurs when there is an abnormal growth of skin cells, usually triggered by damage to the DNA within the skin cells. It is primarily caused by exposure to ultraviolet (UV) radiation from the sun or artificial sources like tanning beds. Skin cancer is the most common type of cancer worldwide, and its incidence continues to rise.
Basal Cell Carcinoma (BCC): BCC is the most common type of skin cancer, accounting for about 80% of cases. It typically develops in...
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Renewal of Skin Epidermal Stem Cells01:12

Renewal of Skin Epidermal Stem Cells

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The skin is divided into epidermis, dermis, and hypodermis, the skin's outermost, middle, and inner layers. The human epidermal layer regularly undergoes renewal, where old, dead cells are replaced by new cells. Epidermal stem cells or EpiSCs divide and differentiate to restore the lost cells. For the renewal process, some EpiSCs continuously self-renew. In contrast, few others differentiate into transit-amplifying cells, which later form prickle or spinous cells, followed by granular...
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Pigmentation01:19

Pigmentation

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The color of the skin is influenced by a number of pigments, including melanin, carotene, and hemoglobin. Recall that melanin is produced by cells called melanocytes, which are found scattered throughout the stratum basale of the epidermis. The melanin is transferred to the keratinocytes via melanosomes.
Melanin occurs in two primary forms: eumelanin that provides black and brown pigment and pheomelanin that provides red color. Dark-skinned individuals produce more melanin than those with pale...
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Layers of the Epidermis01:21

Layers of the Epidermis

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The epidermis, the outermost layer of the skin, is composed of several distinct layers. From deep to superficial, the layers of the epidermis are as follows:
Stratum Basale
Stratum basale, also known as the stratum germinativum, is the deepest layer of the epidermis. It is composed of a single layer of actively dividing cells called basal cells or basal keratinocytes. These cells constantly undergo cell division to replenish the upper layers of the epidermis. Additionally, melanocytes, which...
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Related Experiment Video

Updated: Mar 31, 2026

Characterization of In Vitro Differentiation of Human Primary Keratinocytes by RNA-Seq Analysis
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Characterization of In Vitro Differentiation of Human Primary Keratinocytes by RNA-Seq Analysis

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Porokeratosis ptychotropica.

Linda Y S Jans1, Sebastiaan A S van der Bent1

  • 1Department of dermatology, Alrijne Hospital, Leiden, The Netherlands.

The British Journal of Dermatology
|March 30, 2026
PubMed
Summary

A rare skin condition, porokeratosis ptychotropica, presented as itchy, discolored bumps in the perianal area for two decades. Histology confirmed the diagnosis, revealing characteristic skin changes.

Area of Science:

  • Dermatology
  • Histopathology

Background:

  • Porokeratosis ptychotropica is a rare variant of porokeratosis.
  • It typically affects the perianal and intertriginous areas.
  • Lesions are often chronic and resistant to treatment.

Purpose of the Study:

  • To report a case of porokeratosis ptychotropica.
  • To highlight the clinical and histological features of this rare condition.

Main Methods:

  • Clinical presentation of a 70-year-old male patient with a 20-year history of perianal lesions.
  • Histopathological examination of skin biopsy.
  • Diagnosis based on clinical and histological findings.

Main Results:

  • The patient presented with pruritic, hyperpigmented, flat papules and annular plaques with squamous borders in the perianal region.

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  • Histology showed characteristic cornoid lamellae, underlying dyskeratosis, and a sparse perivascular lymphocytic infiltrate.
  • The diagnosis of porokeratosis ptychotropica was established.

    • Conclusions:

    • Porokeratosis ptychotropica is a rare but distinct clinical entity.
    • Characteristic histological features are crucial for diagnosis.
    • This case underscores the importance of considering rare diagnoses in chronic, treatment-resistant skin conditions.