Medical Matters/Dr Muiris Houston: A number of readers have requested a column on cellulitis, a spreading bacterial infection of the skin and the subcutaneous structures
This week I will look at a range of infections that can affect skin and soft tissue. It is an area full of different and, it has to be said, sometimes confusing terminology. Probably the best approach is to consider the various structures in skin and how they can be affected.
Starting from the outside, a hair follicle can become infected, usually with a bacterium called staphylococcus aureus, leading to folliculitis. It manifests with raised skin lesions containing a yellow fluid. Folliculitis is most commonly seen in the beard area in people who shave and is thought to be caused by short curling hairs growing back into the skin. The resulting irritation leads to infection.
Impetigo is a common infection of the epidermis or upper layer of skin. Usually the result of colonisation by the staphylococcus aureus bug, it can also arise from a mixed infection. In the early stages a purulent blister forms; this then ruptures, leading to weeping and the formation of golden crusted areas on the skin. The face and hands are the commonest places where impetigo develops.
Children, in particular, transfer the infection from hand to mouth, and to each other. On many occasions I have been faced with a number of brothers and sisters with the classic crusted appearance of impetigo. Because it is highly infectious, children should be kept away from school until the impetigo has cleared up.
Treatment consists of both topical and oral antibiotics and must be continued until the infection is no longer visible. In cases where the problem recurs, the bacteria may be hiding in the nostril and your doctor may prescribe a topical antibiotic ointment for the inside of the nose.
Cellulitis, a spreading bacterial infection of the skin, causes local signs of inflammation such as heat, redness and pain. As it spreads, local lymph nodes may enlarge. Eventually, the patient feels unwell and runs a high temperature. Blood tests will show a raised white cell count, confirming that the body is fighting infection.
When cellulitis spreads through the blood system it requires hospital treatment with intravenous antibiotics. Until the bacteria is identified - the commonest culprits being streptococcus pyogenes and staphylococcus aureus - the antibiotic flucloxacillin is the first choice treatment. In severe cases benzylpencillin is added to bring the spreading infection under control. The problem can be recurrent if the lymphatic system is blocked and damaged.
Erysipelas differs from cellulitis in that it tends to be a more superficial infection; in addition it has a clearly demarcated edge. While cellulitis most commonly affects the lower limbs, erysipelas affects the shins, face and scalp. Occasionally, it recurs at one particular site leaving a permanent oedematous mark. According to one study, 30 per cent of people with erysipelas have a recurrent episode within three years. Risk factors for both erysipelas and cellulitis are the presence of oedema, leg ulcers or wounds following trauma.
Some years ago, there was considerable media attention on the evocatively named "flesh-eating disease". The proper name for this condition is necrotising fasciitis. It affects the deeper layers of skin as well as muscle. Strep. pyogenes is just one possible cause, with bugs that like oxygen-free conditions also to blame. It progresses rapidly and can be fatal. Effective treatment depends on removing the affected tissue along with the use of a triple cocktail of antibiotics. It is a rare disease.
The skin is also a window to infection in other bodily systems. The classic rash of meningitis and meningococcal septicaemia - pinprick lesions which do not blanche when a clear glass is pressed on them - is an example of how skin appearance can alert parents and doctors to the presence of a life-threatening disease.
Many viruses also cause skin rashes. Chickenpox and measles produce rashes that are characteristic in both appearance and location. In herpes simplex infections cold sores are often the first sign of disease. Many viruses produce a non-specific, generalised red rash which disappears quickly once the acute phase of the viral illness is over.
While the eye may be the window of the soul, I hope this brief description of some skin infections shows how the skin is often a reflection of bodily illness.
You can email Dr Muisin Houston at mhouston@irish-times.ie. He regrets he cannot answer individual queries