Erythrasma
Colonization with Corynebacterium minutissimum
can lead to this dry, orange–brown rash that usually
affects the flexural creases such as the toe webs
or axillae. The affected skin will fluoresce coral
pink under Wood’s light. Erythrasma clears when
treated with topical or oral antibiotics, including
erythromycin or tetracyclines.
Pitted keratolysis
This is a proliferation of corynebacteria that frequently
involves the soles of the feet, exacerbated by tightfitting
footwear and excessive sweating. It may lead to
small, punched-out lesions, a foul-smelling odour, and
discoloured and pitted nails. Improved hygiene will limit
the problem. Topical antimicrobials, e.g. clindamycin,
1:10 000 aqueous potassium permanganate foot soaks,
and antiperspirants, such as aluminium chloride,
may help.
Staphylococcal infections
Impetigo
Impetigo is a highly contagious skin disease that
most commonly affects schoolchildren. It is usually
caused by staphylococci, but group A streptococci
can also cause this clinical picture, so skin swabs
should be taken to determine the cause and guide
treatment. It presents as superficial exudative lesions
that develop a characteristic yellow crust (Fig. 7.13).
The lesions spread rapidly. Occasionally the bacteria
produce toxins that cause the lesions to blister
(bullous impetigo). The lesions may complicate
other skin disorders such as atopic eczema and
herpes simplex. Management involves topical fusidic
acid and antiseptics applied to localized disease.
Children should be kept off school for 1 week after
the lesions first crust, and picking of the lesions
should be discouraged. If the infection becomes
widespread, systemic antibiotics are necessary. Withthe most serious form of impetigo, that caused by
Streptococcus pyogenes, oral penicillin is given to
prevent glomerulonephritic complications.
Ecthyma
Ecthyma is an uncommon disease resulting
from cutaneous infection with Staph. aureus or
streptococci. It presents as round, well-demarcated
ulcerative lesions, usually on the legs. After treatment
with systemic antibiotics the ulcers crust over and
scar upon healing. The disease is associated with
poor hygiene and states of malnutrition, and is
more commonly seen in developing countries,
and in the Western world among IV drug users and
immunosuppressed patients.
Folliculitis
Folliculitis is an inflammation of the hair follicle that
presents with itchy or tender papules or pustules. It
is often caused by infection with Staph. aureus. The
pustules have erythematous edges and often contain
an emerging hair shaft. Management is with topical
antiseptics and antibiotics, or systemic antibiotics;
to prevent recurrence the patient should be educated
about improved hygiene.
Streptococcal infections
Erysipelas
Presenting with localized erythema, swelling and
tenderness, erysipelas is an acute infection of the
dermis and the upper subcutaneous layer, usually
caused by streptococci. The inflammation is well
defined and may have palpable borders. It occurs
with general malaise and flu-like symptoms. The
clinical picture in erysipelas overlaps with that
of cellulitis. The eruptions usually clear within 2–3 weeks of treatment with oral or intravenous
penicillin to prevent haematogenous systemic spread
and streptococcal septicaemia. Penicillin can also be
used prophylactically in recurrent cases; these lead to
lymphatic damage and irreversible oedema.
Cellulitis
This is an infection of the deep subcutaneous layer of
the skin, usually by streptococci. The area becomes
erythematous, hot and tender to the touch, and the
infection can spread rapidly. Patients are
systemically unwell and pyrexial. Infection can arise
from breaks in the skin barrier, such as IV catheters,
wounds, surgical incisions or leg ulcers, and injection
sites in IV drug users. Broad-spectrum antibiotic cover
should be initiated as soon as possible until the results
of blood cultures yield the organism and its antibiotic
sensitivities. Any identified underlying cause should
be treated. It is common practice to draw around the
site of erythema on the skin, as this allows monitoring
of any spread and response to treatment.
Necrotizing fasciitis
This serious infection may occur after minor trauma;
it must be treated immediately to prevent serious skin
necrosis in the affected area and death. The infection
is characterized by a high fever and an ill-defined
erythema that usually occurs on the leg. High-dose IV
antibiotics and surgical debridement of the necrotic
tissue are required.
Mycobacterial infections
Lupus vulgaris
This condition, which is now very rare in the Western
world, is the most common type of cutaneous TB. It
arises as a postprimary infection and usually begins in childhood. Painless, red–brown nodules form, which
scar and heal slowly. They can coalesce to form larger,
erythematous plaques, which are most commonly
seen on the head and neck. Complications include
the destruction of deeper skin tissues and the
increased risk of developing squamous cell carcinoma
in chronic lesions. A biopsy will aid the diagnosis and
the Mantoux test is positive. Treatment is that for the
eradication of TB.
Scrofuloderma
This is an infection that occurs on the skin overlying
a lymph node infected with TB, or an affected bone
or joint. A dull red nodule develops, which ulcerates
and can lead to fistulae, granulation, scarring and
discharge.
Warty tuberculosis
This results from the inoculation of TB into the skin
of previously infected patients. It forms warty plaques
on cold erythematous areas, commonly of the hands,
knees and buttocks. The condition is now extremely
rare in the Western world, but is still common in
developing countries.
Spirochaetal infections
Secondary syphilis
The secondary stage of syphilis begins 1–3 months
after the primary chancre, and is characterized by
pink or copper-coloured papules that appear on the
trunk, palms, limbs and soles. The papules resolve
spontaneously in 1–3 months without treatment.
Yaws/bejel/pinta
These non-venereal treponemal infections are
endemic in tropical developing countries. In all three
serology is positive for syphilis, and the infection may
be treated with penicillin.
Lyme disease
This condition is caused by Borrelia burgdorferi and
is spread by tick bites. Lyme disease is characterized
by a slowly expanding erythematous ring at the site
of the initial bite. Complications include arthritis,
neurological pathology and cardiac sequelae.
Treatment is with penicillin or tetracycline.
Other bacterial infections
Anthrax
Primarily a disease of animals, anthrax causes
haemorrhagic bullae at the site of inoculation. The
lesions are accompanied by oedema and fever. The
Cellulitis. diagnosis is made by culture of blister fluid and the disease is treated by intramuscular injections of
penicillin or intravenous tetracycline (followed by an
oral course).
Gram-negative infections
Gram-negative bacilli, such as Pseudomonas aeruginosa,
may secondarily infect skin wounds such as leg ulcers.
They may also cause nail discoloration, folliculitis
and, occasionally, cellulitis.