What is ecthyma?
Ecthyma is a local bacterial infection of the skin caused by the same bacteria that are also responsible for impetigo (school sores). There is also a variant of ecthyma caused by the Pseudomonas bacterium (Pseudomonas aeruginosa); this form is also called ecthyma gangrenosum and occurs almost only in people with a strongly reduced immune system.
What does it look like?
Ecthyma begins as a red, weeping patch in which a blister-like lesion can arise. The colour can become deep purple. Often the blister dries into a thick crust. On removal of the crust, there is often a fairly deep wound underneath filled with pus.
What causes it?
Ecthyma is caused by bacteria from the streptococcus and staphylococcus families. In most cases a streptococcus is found, and in about 85% a staphylococcus as well. Much more rarely, ecthyma-like lesions are caused by the Pseudomonas aeruginosa bacterium (ecthyma gangrenosum).
Who gets it?
Ecthyma can occur at any age but is seen relatively often in children and young adults. The preferred site is the lower legs. The presence of small skin injuries (insect bites, scratches) considerably increases the risk of developing ecthyma. People with reduced resistance also have an increased risk.
How is it treated?
When a crust is present on the ecthyma it should first be removed. Small ecthymas can sometimes be healed with regular care using povidone-iodine ointment or with topical antibiotic ointment (such as fusidic acid). For more extensive lesions an oral course of antibiotics is indicated. After healing, washing the skin with a disinfecting soap is useful to prevent new infections.
When to see a doctor
See your GP if you develop a crusted sore that deepens into an ulcer, especially on the lower legs, or if such a sore is spreading, painful or not healing. People with a weakened immune system, or anyone who becomes feverish and unwell, should seek care promptly, as the infection can occasionally be serious.