Skin infections

Staphylococcal infections

Most skin infections are staphylococcal and relatively minor. They will settle with no specific treatment; topical antiseptics may be used or systemic antibiotics if the infection does not settle or spreads. Patients with unexplained infections should be checked for diabetes mellitus. The sensitivity of the organisms is determined so that the appropriate antibiotic can be chosen should the need arise. Incision and drainage are indicated when pus is present. If severe, lyrnphangitis or cellulitis can develop. Various clinical presentations exist.

Boil (syn. furuncle) is an infection of a pilosebaceous unit with perifolliculitis, which usually proceeds to suppuration and central necrosis. A ‘blind boil’ is one that subsides without suppuration. Boils are common on the face, head and neck. Boils are frequently associated with overwork, worry, debility or other undermining influences. They may be the presenting symptom of diabetes mellitus.

Furunculosis of the external auditory meatus is extremely painful, as the skin is attached to the underlying cartilage, and swelling is accompanied by considerable tension.

Stye (syn. hordeolum) is due to infection of an eyelash follicle. Should softening occur around a hair follicle, particularly an eyelash, removal of the hair allows the pus to escape.

Carbuncle4 is an infective gangrene of the subcutaneous tissues, which often occurs in the nape of the neck. The subcutaneous tissues become painful and indurated, and the overlying skin is red (Fig. 13.9). Unless the condition is aborted by prompt treatment, extension will occur and, after a few days, areas of softening appear, the skin sloughs and discharges pus. Usually there is one central large slough, surrounded by a ‘rosette’ of smaller areas of necrosis. The general treatment and organism identification are similar to those described for boils. Many carbuncles are aborted if antibiotics are used adequately in the early stages.

Impetigo is an intradermal infection (Fig. 13.10). The primary lesion is bullous, and soon ruptures to form an erosion and then a crust. The

4’Carbunculus’ in Latin, ‘anthrax’ in Greek, is the word for charcoal. The ancients saw in these conditions burning sores upon the skin hence they likened them to glowing coal.

infection is contagious, and in rugby football one player so infected can spread the disease among team mates and the opposing side (the condition being known as scrumpox). Treatment is by careful washing of the face to remove crusts using chlorhexidine soap and lotion (1 per cent); systemic antibiotics are used in those cases that are resistant to local treatment.

Necrotising fasciitis (syn. Meleney’s

streptococcal gangrene, Fournier’s gangrene)

Necrotising fasciitis is a destructive invasive infection of skin, subcutaneous tissue and deep fascia, with relative sparing of muscle. Bacteriology can be polymicrobial involving a synergistic combination of anaerobes and facultative species such as coliforms or nongroup A streptococci; or monomicrobial due to group A beta-haemolytic streptococci. Common sites are the genitalia, groins and lower abdomen (Fig. 13.11a), although necrotising fasciitis has been reported at almost any site. Patients are unwell, febrile, with areas of subcutaneous induration and erythema; surgical emphysema is palpable if gas-forming organisms are involved; necrotic patches of skin develop. Treatment is by wide surgical excision of all affected soft tissues; very large defects can be created (Fig. 13.11b). Antibiotics and supportive therapy are also administered. Mortality is high and is increased if surgical treatment is delayed or insufficiently radical. Necrotising fasciitis can arise without any history of injury, but can also follow operations or more localised infections. Risk factors for the development of this condition include diabetes mellitus, malnutrition, obesity, corticosteroid drugs and immune deficiency.

Hydradenitis suppurativa

Hydradenitis suppurativa (apocrinitis) is a chronic cicatrising suppurative process caused by apocrine gland hyperplasia (Fig. 13.12). It is common in the second and third decades of life and three times more common in women than men. It occurs most commonly in the axilla, but can also affect the groins and perineum. Locally, duct obstruction from keratin plugging occurs leading to rupture of apocrine glands into the dermis and subdermal tissues with subsequent superimposed infection. Pain can be severe. A course of metronidazole has been found to be useful owing to the fact that Bacteroides is a common causative organism; a prolonged course of erythromycin can be curative. If the condition does not respond, then surgical excision is necessary. If a wide area of skin needs to be removed, the wound needs to be covered by a split-skin graft.

Lupus vulgaris

Lupus vulgaris (tuberculosis of the skin) usually occurs between the ages of 10 and 25, the face being the site of election. One or more cutaneous nodules appear, with congestion of the surrounding skin (Fig. 13.13). When blood is expressed with a glass slide, the brownish (apple-jelly) nodules of individual tubercles can be seen. Extension occurs very slowly, but ulceration is likely to follow sooner or later. The resulting ulcer tends to heal in one situation as it extends to another. The mucous membranes of the mouth and nose are sometimes attacked, either primarily or by extension from the face. Oedema occurs if the fibrosis caused by the lupus obstructs the normal lymphatic drainage. Infection in the nasal cavity may be followed by necrosis of underlying cartilage. Treatment is with anti-tuberculous chemotherapy; the lesion should be excised if healing is slow. Squamous cell carcinoma is prone to occur in a lupus scar (Fig. 13.14).