DERMATOLOGY
ages and with invasion of the dermis. Pyodermas are
almost always secondary. Classification of pyoderma
based on depth of bacterial involvement is clinically
the most useful, because it provides information on
diagnosis, differential diagnosis, underlying disease,
prognosis and response to treatment. Pyoderma may
be on the skin surface, affecting the stratum corneum
and outer epidermis (e.g. intertrigo and pyotraumatic
dermatitis); superficial, involving only the epidermis
(e.g. impetigo) and the epithelial appendages in the
dermis (e.g. folliculitis) or deeper, compromising
structures in the dermis and deep, subjacent fatty tissue.
The development of pyoderma occurs in 2 stages.
Firstly the microbes colonise areas of the body surface. This occurs commonly as many skin diseases
are aggravated by microbial colonisation or invasion.
The second phase occurs when the stratum corneum
is invaded to cause impetigo and/or invasion of the
hair follicles causing folliculitis. The latter two are
classified as superficial pyoderma. When the infected
hair follicle ruptures, the infection spreads into the
dermis (furunculosis) or spreads more deeply [ۙ\