Dermatological infectionsDr Daniel HewittDermatologistSkin and Cancer Foundation Westmead
ObjectivesTo understand the different types of organisms that can cause skin pathologyTo appreciate the common clinical presentationsTo understand the important investigationsTo briefly appreciate the ways in which infections and infestations are treated
IntroductionThere are many types of micro-organisms that exist on the skin and in the environment. The normal bacteria and yeasts on the skin are termed commensal organisms.Some organisms can cause skin pathology. The infections or infestations of these organisms have many different clinical presentations.Micro-organisms may also complicate pre- existing skin diseases, such as dermatitis.
The most common organisms causing skin pathology areBacteria Gram positives eg Staphylococcus, Streptococcus Gram negatives eg PseudomonasViruses eg Herpes virusesFungi eg Dermatophyte organismsYeasts eg Candida, MalasseziaParasites eg Lice, scabies
InvestigationsIn all infections, identification of the organism provides confirmation of a diagnosis. There are many ways to do this.Wood’s light – a UV light that causes certain organisms to fluoresce. eg erythrasma shows “coral pink” fluorescence and some fungal infections of the scalp flouoresce green.Scrapings from scaly areas and abnormal nails can be examined microscopically at the bedside or sent to the laboratory to look for yeasts or fungi.Swabs can be examined for bacteria by microscopy and culture. Swabs can also be examined by polymerase chain reaction (PCR) for viruses such as herpes virus.Fresh tissue samples can also be sent for these investigations. Less common organisms such as mycobacteria need special growth media and techniques so the laboratory must be informed of the full range of organisms possibly present.
Erythrasma and the coral pinkfluorescence seen underWood’s light
Bacterial infectionsCellulitisThis is infection of the skin and cutaneous connective tissue.Tender, warm, poorly defined erythema is seen. There may have been a portal of entry eg a cut or break in the skin.Patients may be unwell with fever and raised inflammatory markers.The abdomen and lower legs are common sites.There are many possible causative organisms, but Streptococcus and Staphylococcus are most common
ErysipelasThis is more superficial than cellulitis, causing well defined hot erythema.The face and lower leg are common sites.Streptococcus pyogenes is the most common cause.
Superficial, blistering erythemacharacteristic of erysipelas
ImpetigoThis is a superficial infection of the skin. There is a non- bullous form with yellow crusty erytematous patches and a bullous form with erythema and bullae (blisters.)It is more common in children. The face and limbs are the most common sites.Staphylococcus aureus is the most common cause of bullous impetigo. Streptococcus pyogenes and staphylococcus aureus can cause non-bullous impetigo.
Classic examples of bullous and non-bullous impetigo
FolliculitisThis is inflammation of the follicular unit. It may be due to Gram positive or Gram negative bacteria, yeasts and fungi or non-infective.Staphylococcus aurues and Propionibacterium acnes are the most common organisms grown on swabs.More severe inflammatory nodules may develop – termed furuncles (or boils.) Several of these can coalesce to form a carbuncle.
Virus infectionsWartsThese are caused by the human papilloma virus. There are many different types, such as common, plane and genital warts.They are common in children, but can occur at all ages.Treatments are numerous but generally involve either chemically or physically “burning” the wart or applying a cream (eg imiquimod) to stimulate the patient’s immune system to react against the virus and clear the wart.Treatment is frequently not required, as warts do eventually self-resolve.
Molluscum contagiosumThis is a very common pox virus infection causing umbilicated, flesh coloured papules, most common in infants. They can be spread by close contact but are not highly contagious.Ocassionally they itch, especially in children with eczema. Uncontrolled eczema can also contribute to the lesions spreading.Treatment is not usually required as they self-resolve and cause no medical concerns.In adults they can be a sign of immunodeficiency eg AIDS.
Herpes virusesThere may be itching and pain prior to a vesicle or erosion forming.The virus resides in the nerves and can re-activate to give the cutaneous changes. Crops of punched out ulcers are chracteristic.On the lips this change is commonly known as a “coldsore,” on the fingers it is termed a “herpetic whitlow.”Type I herpes simplex virus is most often associated with facial and finger lesions and Type II is almost exclusively associated with genital lesions.Herpes zoster virus, the cause of chickenpox, can re- activate to cause painful erythematous papules which develop into vesicles and then dried crusts. This eruption is usually dermatomal, most commonly in the thoracic area. It is also known as shingles.
Many other viruses can cause skin changes.An exanthem is a fever characterised by a skin eruption. These are caused by virsues and usually have distinguishing features. Some of these are now much less common due to immunization. Examples inlcude Measles Rubella Pityriasis rosea Erythema infectiosum Roseola infantum Gianotti-Crosti syndrome Hand, foot and mouth disease
Fungal infectionsFungal infections are common and easily missed. They should be considered in any scaling or itchy rash where no other reason (eg dermatitis) is identified.Skin scrapings should be taken from such lesions and sent for fungal microscopy and culture. A blade is scraped across the skin and skin scales collected – this is a very simple but important test that is under-utilised.If the nails are involved, clippings of these should also be sent.
Fungi can infect any part of the skin, the hair and the nails.Infections of the body, commonly known as “ringworm” are not worm infections and more precisely known as Tinea. The location is specified in the diagnosis. eg Tinea capitis Scalp infection Tinea corporis Body infection TInea pedis Foot infection Tinea manuum Hand infectionTinea of the nails is known as onychomycosis
Infections can be acquired from pets, from the environment or from other people.The most characterisitic feature is a annular plaque with a raised, red border and a trailing scale. Itch is usual.Sometimes, especially if there has been treatment with topical steroids, the appearance is much less specific.In the scalp there is usually less characteristic scaling and erythema.In the nails there is often thickening and crumbling of the nail with scaling of the nail bed – termed “subungual hyperkeratosis.”
Treatment involves either topical or systemic antifungals.Skin infections are often cleared over four weeks with topical terbinafine.Systemic treatment is generally required for up to six months to clear onychomycosis and for six weeks for tinea capitis.
Yeast infectionsPityriasis versicolorThis is a very common rash due to overgrowth of a yeast – Malassezia furfur.It is most common in young adult males and usually arises in hotter weather, especially after the patient has been sweating.Brown or light reg scaly macules develop on the trunk. It darker skins, hypopigmented macules develop.It may be slightly itchy.There are many effective treatments such as pevaryl foaming lotion (econazole) or selsun shampoo. The pigmentary changes can last for several months even when the active yeast proliferation is effecetively treated.
Candida infectionsCandida commonly infects intertriginous areas (areas where the skin is moist and rubbing together) such as the groin and under the breasts.There is weeping erythema, and often separate, peripheral erythematous “satellite” pustules.It may be a superimposed factor in other causes of intertrigo eg dermatitis or seborrheic dermatitis.Candida can also infect the nails, but is most frequently isolated in the nails as a commensal organism.
Parasite infestationsThe two most commonly seen are lice and scabies
Pediculosis (Lice)These are wingless insects that infect the head, the body or the pubic area.Head lice are very common and transmitted via combs, brushes, hats and close contact. Lice feed on the scalp and can produce irritation and itch.Over the counter treatments are effective but are ideally combined with frequent combing to remove the lice eggs (“nits”) and may need to be repeated.
ScabiesThis produces burrows (5-10mm long ridges) and papules, often around the hands, nipples and genitalia. The diagnosis is easily missed as these signs can be very subtle or absent.Itching occurs two weeks after initial infestation. It is often widespread and severe, especially at night. The scabies mite requires a human host, so it can only be acquired via contact with an infected person.It is particularly prevalent in crowded communities such as nursing homes and is endemic throughout many Aboriginal communities.All household members must be treated simultaneously to prevent re-infection.
ConclusionsInfections of the skin are numerous and varied, involving bacteria, viruses, fungi, yeasts and parasites.They can be easily missed if not considered, but once diagnosed, treatment can be curative and highly satisfying.