Infection Of The Skin

A. Yeast Infections

1. Pityriasis Versicolor

This disease is caused by Pityrosporum orbiculare, a gram-positive yeast-like microorganism that is usually a skin commensal. In some individuals, the organism can become pathogenic. Pityrosporum versicolor often affects young adults, causing brown scaly macules on the trunk and sometimes on the limbs. Carboxylic acids released by the organisms inhibit melanogenesis and thus the affected areas may appear relatively pale following exposure to sunlight. The infection may be demonstrated by microscopy of skin scrapings suitably treated with potassium hydroxide solution.

Most patients will respond to a topical imidazole drug, such as miconazole, clotrimazole, or econazole creams, applied once daily for 6 weeks. Ketoconazole shampoo can also be used to wash the affected areas daily for 4-5 days. Other effective topical treatments include Whitfield's ointment (6% benzoic acid and 3% salicylic acid in emulsifying ointment), selenium sulfide shampoo, and 20% sodium thiosulfate solution.

2. Candida

The yeast Candida albicans may cause vulvovaginitis in women, especially during pregnancy, in those taking oral contraceptives, or those who are receiving systemic antibiotics for acne. It may also cause stomatitis in infants, and may exacerbate intertrigo in the body folds of obese individuals and the napkin area during infancy. The nail plate may also be infected, and the organism may cause chronic paronychia in those involved with wet-work such as bar workers or housewives. Topical treatments with imidazole creams is often effective, although more serious infections may require systemic therapy.

B. Dermatophyte Infections

Dermatophyte infection (ringworm) is restricted to invasion of the stratum corneum, nails, and hair. The dermatophytes, Trichophyton, Epidermophyton, and Microsporum species may infect humans. Microsporum species are usually acquired from infected cats or dogs (M. canis) and are a frequent cause of tinea capitis (ringworm affecting the head) in children. Infections from farm or other animals tend to cause more vigorous inflammation than those from other sources. The infection may be diagnosed from microscopy of skin, nail, or hair treated with potassium hydroxide. Alternatively, the fungus may be cultured.

Tinea corporis (ringworm affecting the skin of the trunk or limbs) often presents as a pruritic, annular, erythematous, scaling plaque, which may resemble a patch of eczema or psoriasis, but is often solitary. Tinea cruris (ringworm affecting the groin) presents as a well-demarcated pruritic erythematous scaling rash affecting the groins. The rash may extend onto the thigh and genitalia. Trichophyton rubrum and Epi-dermophyton floccosum are the most common causative fungi. Tinea pedis (ringworm affecting the feet) may affect the skin of the toe web spaces, sole, or may extend onto the sides and dorsal aspect of the feet. Trichophyton rubrum, T. mentagrophytes; and E. floccosum are the most common causative organisms.

Tinea manuum is a chronic form of ringworm affecting the hands (frequently only one palm will be affected); T rubrum is the most commonly identified organism. Tinea unguium (ringworm affecting the nail plate and nail bed) may be caused by T rubrum, T. mentagrophytes, or E. floccosum. Affected nails are often thickened and have a yellowish discoloration. Onycholysis (separation of the nail plate from the nail bed) may also be seen.

Tinea incognito is the term used to describe dermatophyte infections treated inappropriately with topical corticosteroids, which suppress the inflammatory response, but allow the fungus to proliferate.

Topical imidazole creams (e.g., miconazole, econozole, or clotrimazole), which interfere with ergosterol synthesis and thereby impair fungal cell wall permeability, when used twice daily for 2 weeks, are adequate for most limited areas of fungal infection. The more recently introduced topical allylamine terbinafine is also very effective (20). More extensive infections, or involvement of the nail or scalp will require systemic therapy.

C. Bacterial Infections

Various acute bacterial infections may affect the skin. These include impetigo, erysipelas, cellulitis, furuncles, carbuncles, anthrax, diphtheria, and various mycobac-terial infections, including tuberculosis and leprosy. Of these only impetigo (in which a small area is infected) or furuncles, which are both caused by Staphylococcus aureus, are amenable to topical treatment. In impetigo, which is more common in young children, an inflamed erythematous area with a yellow crust may develop on exposed skin. Local treatment with antibiotic washes, such as Phisomed or Hibiscrub, and topical mupirocin or fucidic acid (Fucidin) ointment may be sufficient. More extensive areas, larger than a few centimetres in diameter, will require treatment with systemic antibiotics.

1. Antibiotics

Furuncles are hair follicles infected with S. aureus and present as yellow-headed pustules. They are commonly seen on the back of the neck in men or in patients treated with ointments or tar (particularly if the skin has been occluded). Extensive areas of folliculitis (furuncles) will require systemic floxacillin (flucoxacillin), but solitary or isolated lesions will respond to topical mupirocin or sodium fusidate (Fucidin). Mupirocin (pseudomonic acid) interferes with bacterial protein synthesis, has the advantage of no cross-resistance with other antibiotics and is available only as a topical preparation. It is effective against both staphylococci and streptococci and may be used in the treatment of folliculitis, infected eczema, and as prophylaxis against nasal carriage of staphylococci. Fucidic acid inhibits bacterial protein synthesis and is particularly effective against staphylococcal skin infections. Topical application may lead to a hypersensitivity reaction. Metronidazole inhibits DNA synthesis and is active against anaerobic bacteria and protozoa, and it can be used topically in the treatment of rosacea. It has also been used to reduce the smell of infected, sloughy ulcers.

2. Antiseptics

Antiseptics have bactericidal activity and may be used as cleansing agents on the skin, as an adjunct to antibiotic therapy, or to prevent secondary bacterial infection. Povidone iodine is a powerful bactericide and may also be effective against viruses. It is commonly used preoperatively to minimize the chance of sepsis, and it may also be of help in the treatment of leg ulcers and herpetic lesions. Potassium permanganate 1:8,000 or 1:10,000 aqueous solution is an effective antiseptic that may be used as a soak in the treatment of infected or weeping eczema. Potassium permanganate also acts as an astringent which helps ''dry up'' exudative or weeping rashes. Chlorhexidine is an effective skin disinfectant and is available in a wide range of preparations.

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Responses

  • Dodinas Baggins
    Can you have pityriasis with yeast on straum corneum and in follicles with no lesions?
    6 months ago

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