Part II. Special dermatology

After studying the topic, the student should

know:

• classification of pyoderma;
• etiology, pathogenesis, epidemiology;
• clinical picture of pyoderma;
• principles of systemic and topical therapy;
• prevention of relapses of the main forms of pyoderma;

be competent in:

• examining a patient and determining the elements of the rash;
• making a preliminary diagnosis;
• planning the examination of a patient;
• prescribing treatment;
• prescribing preventive measures.

Pyoderma (synonyms: pustular skin diseases, pyodermia, from the Greek pyon [pus] + derma [skin]) is an acute (rarely chronic) purulent inflammation of the skin, its appendages, and subcutaneous fat, caused predominantly by staphylococci and streptococci, less often, by Pseudomonas aeruginosa, pneumococci, E. coli, etc.

Epidemiology. Pyoderma is the most common skin disease at any age, accounting for up to 30–40% of all skin diseases. The apparent cause is the abundance of staphylococci and streptococci in the human environment (in the air, dust of premises, on clothing, and on human skin).

Etiology and pathogenesis. Pyoderma is caused by staphylococci and streptococci from gram-positive microbial flora. Of all the variety of staphylococci, the most significant is Staphylococcus aureus. Staphylococci are facultative anaerobes; they colonize the epidermis, especially in the ostium of hair follicles, sebaceous and sweat glands.

Streptococci on human skin are less common than staphylococci, occupying mainly the smooth skin and natural holes and folds. Streptococci are obligate aerobes, while β-hemolytic (Streptococcus haemolyticus-β) is pathogenic. Staphylococci and streptococci induce the skin suppuration by the release of various metabolic products (exotoxins, enterotoxins, enzymes, etc.).

Pyogenic cocci infect the skin mostly exogenously. Intact, clean skin serves as a reliable barrier to prevent bacteria penetration. In the damaged epidermis (abrasions, fissures, scuffs), skin contamination, violation of the composition of sweat, changes of pH in the water-lipid mantle of the skin, changes in the composition and quantity of sebaceous secretions, or improper skin care, the protective function of the skin is disrupted.

Hypothermia, overheating, and maceration of the skin play a certain role. A cause of chronic pyoderma is the long-term use of GCs for various pathologies. Several endogenous factors also contribute to the disease: a decrease in the immune defense of the body and in the immunological control system in the skin; various chronic somatic diseases:

• Endocrinopathy (diabetes mellitus, hyperandrogenism, etc.);
• Digestive tract and liver diseases;
• Focal infections;
• Blood diseases;
• Vitamin imbalance;
• Severe diseases that lead to exhaustion, including HIV infection.

Pyoderma often complicates the course of several chronic itchy skin diseases, including scabies, eczema, neurodermatitis, AtD (secondary pyoderma).

Classification. In Russian dermatology, the classification of pyoderma proposed by A. Jadassohn (1949) modified by A.A. Kalamkaryan (1954) and S.T. Pavlov (1957) divides pyoderma, depending on the traditional etiological principle. into staphyloderma, streptoderma, and strepto-staphyloderma (Tables 7.1, 7.2). The disease can be acute or chronic; the lesion can be superficial or deep; the mechanism can be primary and secondary.

Table 7.1. Classification of pyoderma