Pathogenesis and Localization Features
The group of superficial mycoses, also known as keratomycoses, is distinguished by an extremely low degree of contagiousness. This means that the risk of infection transmission from person to person is minimal.
The pathological process in these diseases is strictly limited. Keratomycetic fungi develop only in dead, keratinized tissues. Their main habitats and breeding zones are the superficial sections of the stratum corneum of the epidermis (smooth skin) as well as the cuticle (surface) of the hair. At the same time, the pathogens lack the ability to penetrate the deep layers of the epidermis, dermis, hair follicle, or hair cortex, which largely determines the mild clinical presentation and specific treatment.
Major Causative Agents of Keratomycoses
Depending on the localization of the lesion, keratomycetes can be divided into two main groups: those affecting smooth skin and those affecting hair. In the affected tissues, they form specific morphological structures.
Fungi affecting the epidermis of smooth skin:
- Malassezia furfur. The causative agent of tinea versicolor. Microscopic examination of the stratum corneum reveals short, slightly curved hyphae combined with yeast-like cells.
- Phaeoanellomyces werneckii. Causes a condition known as tinea nigra. In the tissues of the stratum corneum, this pathogen appears as dark, septate hyphae and budding cells.
Fungi affecting hair (causative agents of piedra):
- Piedraia hortae. The causative agent of black piedra. Clinically manifested by the formation of hard black nodules on the hair surface. Microscopically, asci (sacs) are identified within these nodules.
- Trichosporon beigelii. Causes white piedra. Characteristic yellowish nodules form around the hair shaft. They consist of mycelial fragments and arthroconidia.
Principles of Treatment for Superficial Mycoses
Given the superficial localization of the pathogen, the treatment of keratomycoses is based on a combination of two approaches: mechanical removal of the affected tissues and local pharmacotherapy.
The main strategy consists of active exfoliation of infected scales using keratolytic agents. The treatment regimens include the following drug groups:
- Keratolytics and antiseptics. Preparations containing selenium disulfide, sodium thiosulfate, or salicylic acid. They promote the loosening and removal of the stratum corneum along with the fungal elements.
- Polyene antifungal antibiotics. A representative of this group is amphotericin B.
- Synthetic antimycotics. Miconazole nitrate is used most actively.
Mechanism of action of synthetic antimycotics (using miconazole nitrate as an example) is the direct inhibition of ergosterol synthesis. Ergosterol is a vital structural component of the fungal cell membrane; without it, the membrane loses its integrity, leading to the death of the pathogen.
In specific hair infections caused by Piedraia hortae or Trichosporon beigelii, pharmacotherapy may be insufficiently effective due to the formation of dense nodules. In such cases, the most effective measure is the mechanical shaving of the affected hair combined with strict adherence to personal hygiene rules.