Fungal Infections of the Skin



Fungal Infections of the Skin


Virginia P. Arcangelo



Fungi live in the dead, horny outer layer of the skin. The organisms penetrate only the stratum corneum—the surface layer of the skin—and infect the skin, hair, and nails. They cause tinea, tinea versicolor, and candidiasis.


TINEA

Dermatophytes are a group of fungi that infect nonviable keratinized cutaneous tissues. Dermatophytosis, more commonly called tinea, is a condition caused by dermatophytes. Tinea is further classified by the location of the infection (Box 12.1).

Tinea capitis primarily affects children ages 3 to 9. This age group may also be infected with tinea corporis. Tinea pedis most commonly affects the adolescent population and young adults. Immunocompromised patients have an increased incidence and more intractable dermatophytosis. Tinea unguium, infection of the nails, is also called onychomycosis. It is caused by various yeast, fungi, and molds.


CAUSES

General factors that predispose to fungal infections include warm, moist, occluded environments, family history, and a compromised immune system. Infection is spread from person to person by animals, especially cats and dogs, and by inanimate objects.



PATHOPHYSIOLOGY

Dermatophytes grow only on or within keratinized structures. Most infections result from five specific species of fungus: Trichophyton rubrum, Trichophyton tonsurans, Trichophyton mentagrophytes, Microsporum canis, and Epidermophyton floccosum. These can be found on humans, on animals, and in the soil. They produce enzymes (keratinases) that allow them to digest keratin, causing epidermal scale; thickened, crumbly nails; or hair loss.


DIAGNOSTIC CRITERIA

General symptoms of fungal infections in hair and skin include pruritus, burning, and stinging of the scalp or skin. An inflammatory dermal reaction may cause erythema and vesicles. Diagnosis is confirmed by several mechanisms. One mechanism is microscopic evaluation of the stratum corneum with 10% potassium hydroxide (KOH) preparation. At the margin of the lesion, scale is scraped with a No. 15 knife blade and placed on a slide. KOH is then added and the slide inspected under the microscope. Fungi appear as rod-shaped filaments with branching.

Another mechanism for diagnosis is the fungal culture. A specimen of infected tissue is applied to a dermatophyte test medium on an agar plate. If the infecting organism is a fungus, the plate will change color—from yellow to pink or red—in approximately 2 weeks.

A third diagnostic method involves using a Wood lamp, which produces a bright green fluorescence in the presence of a tinea infection caused by Microsporum species. A major disadvantage of this test is that other fungal infections may be undiagnosed because the Wood lamp test identifies only Microsporum.


Tinea Capitis

Presentation of tinea capitis varies widely. There may be generalized, diffuse seborrheic dermatitis-like scalp scaling, although more common signs and symptoms include impetigo-like
lesions with crusting and redness, areas of hair loss with broken hairs, and possibly inflammatory nodules. Although often impressive, cervical lymphadenitis does not correlate with the extent of scalp inflammation. Finally, approximately 15% of patients have a cross-infection with tinea corporis. Most cases of tinea capitis are found in prepubertal children, with a disproportionate amount in African Americans. It is very contagious.



BOX 12.1
Varieties of Tinea Infections

Tinea infections are identified by their location on the body as follows:



  • Head: tinea capitis


  • Body: tinea corporis


  • Hand: tinea manus


  • Foot: tinea pedis


  • Groin: tinea cruris


  • Nails: tinea unguium (onychomycosis)

Most cases (90%) are caused by T. tonsurans. Microsporum audouinii, spread from human to human, and M. canis, spread from animals, are other organisms.

Tinea capitis presents in several ways:



  • Inflamed, scaly, alopecic patches, especially in infants


  • Diffuse scaling with multiple round areas with alopecia secondary to broken hair shafts, leaving residual black stumps


  • “Gray patch” type with round, scaly plaques of alopecia in which the hair shaft is broken off close to the surface


  • Tender, pustular nodules


Tinea Corporis

Tinea corporis is called “ringworm” when it affects the face, limbs, or trunk, but not the groin, hands, or feet. The typical presentation of tinea corporis is a ring-shaped lesion with well-demarcated margins, central clearing, and a scaly, erythematous border. It is caused by contact with infected animals, by human-to-human transmission, and from infected mats in wrestling. The organisms responsible are M. canis, T. rubrum, and T. mentagrophytes.


Tinea Cruris

Tinea cruris is often referred to as jock itch. A fungal infection of the groin and inguinal folds, tinea cruris spares the scrotum. The most common causes are T. rubrum or E. floccosum. Typically, the lesion borders are well demarcated and peripherally spreading. The lesions are large, erythematous, and macular, with a central clearing. A hallmark of tinea cruris is pruritus or a burning sensation. There is often an accompanying fungal infection of the feet.


Tinea Pedis

Interdigital tinea pedis, commonly called athlete’s foot, is characterized by scaling and itching in the web spaces between the toes and sometimes denudation and sodden maceration of the skin. Another variation is inflammatory tinea pedis, which presents with vesicles involving the toes or instep. A third variety is the moccasin style, which presents with itching, chronic noninflammatory scaling, and thickness and cracking of the epidermis on the sole, heel, and often up the side of the foot. This is a common problem in young men.

Most cases are caused by T. rubrum, which evokes a minimal inflammatory response. The T. mentagrophytes organism produces vesicles and bullae.

There are three types of tinea pedis:



  • Interdigital, which presents as scaling, maceration, and fissures between the toes


  • Plantar, which presents as diffuse scaling of the soles, usually on the entire plantar surface


  • Acute vesicular, which presents as vesicles and bullae on the sole of the foot, the great toe, and the instep


Tinea Manus

Tinea manus is a dermatophyte infection of the hand. This is always associated with tinea pedis and is usually unilateral. The lesions are marked by mild, diffuse scaling of the palmar skin, and vesicles may be grouped on the palms or fingernails involved.


Tinea Unguium

Tinea unguium (onychomycosis) is a fungal infection of the nail. Typically affected are the toenails, which become thick and scaly with subungual debris. Onycholysis, a separation of the nail from the nail bed, may be seen. The infection usually begins distally at the tip of the toe and moves proximally and through the nail plate, producing a yellowish discoloration and striations in the actual nail. Under the nail, a hyperkeratotic substance accumulates that lifts the nail up. If untreated, the nail thickens and turns yellowish brown. Onychomycosis is usually asymptomatic but can act as a portal of entry for a more serious bacterial infection.

Organisms causing onychomycosis include dermatophytes, E. floccosum, T. rubrum, T. mentagrophytes, Candida albicans, Aspergillus, Fusarium, and Scopulariopsis.

Some health insurance plans refuse to reimburse for drug therapy without confirmation of the diagnosis. Tests that verify the diagnosis include the KOH test and culture.


INITIATING DRUG THERAPY

Fungal infections can be prevented by applying powder containing miconazole (Monistat) or tolnaftate (Tinactin) to areas prone to fungal infections after bathing. The areas can be dried completely with a hair dryer on low heat.



Goals of Drug Therapy

Pharmacologic therapy is directed against the offending fungus and the site of infection. Therapy is topical or systemic, depending on the location of the lesion. Topical therapy is used for most skin infections. The exceptions are tinea capitis and tinea unguium (onychomycosis).


Topical Azole Antifungals

Topical azoles (Table 12.1) impair the synthesis of ergosterol, the main sterol of fungal cell membranes. This allows for increased permeability and leakage of cellular components and results in cell death. Topical azoles are fungicides that are effective against tinea corporis, tinea cruris, and tinea pedis as well as cutaneous candidiasis. They should be applied once or twice a day for 2 to 4 weeks. Therapy should continue for 1 week after the lesions clear. However, therapy is not recommended during pregnancy or lactation and is administered cautiously in hepatocellular failure. Ketoconazole (Nizoral), in particular, should be avoided in patients with sulfite sensitivity. Adverse effects include pruritus, irritation, and stinging.


Topical Allylamine Antifungals

These agents are effective against dermatophyte infections but have limited effectiveness against yeast. Patients treated with these agents may undergo a shorter treatment period with less likelihood of relapse. Topical allylamines are applied twice daily. Potential side effects include burning and irritation.








TABLE 12.1 Overview of Antifungal Medications





































































































Generic (Trade) Name and Dosage

Selected Adverse Events

Contraindications

Special Considerations


Topical Agents


clotrimazole ointment (Lotrimin), powder (Desenex). Gently massage ointment into affected and surrounding skin areas bid × 4 wk; powder as needed.

Erythema, irritation, stinging, pruritus

Pregnancy or lactation


Use cautiously in patients with hepatocellular failure

May be purchased OTC


miconazole (Micatin, Monistat Derm). Cover affected areas with cream lotion or powder bid for 2-4 wk.

Irritation, maceration

Pregnancy or lactation

Avoid applying near eyes.


ketoconazole (Nizoral). Apply to affected and surrounding areas once daily for 2-4 wk.

Irritation, stinging, pruritus

Asthma


Not administered to people who are sensitive to sulfites


Pregnancy or lactation

Not recommended in children


oxiconazole (Oxistat). Apply to affected and surrounding areas one to two times daily for 2-4 wk.

Pruritus, burning

Pregnancy or lactation

Avoid applying near eyes or mucous membranes.


sulconazole (Exelderm). Apply to affected and surrounding areas bid × 4 wk.

Pruritus, burning sensation, erythema

Pregnancy or lactation

Not recommended in children


Avoid contact with eyes.


ciclopirox (Loprox). Apply to affected area bid × 4 wk.

Pruritus, burning sensation


Not recommended in children younger than age 10


Lotion formulation good for nails


Avoid occlusive dressing.


naftifine (Naftin). Apply to affected area once daily × 4 wk

Burning, stinging, dryness, erythema, itching


Not recommended in children


Avoid occlusive dressings.


Avoid contact with mucous membranes.


terbinafine (Lamisil). Apply to affected area bid × 4 wk.

Burning, irritation, skin exfoliation, dryness


Not recommended in children


Avoid occlusive dressings.


Avoid contact with mucous membranes.


tolnaftate (Tinactin). Apply small amount bid × 4 wk.

Stinging, burning, irritation


Not recommended in children younger than age 2


selenium sulfide (Selsun) 1% (OTC), 2.5%. Massage into affected area, rest 15 min, and rinse thoroughly

Irritation, hair loss


nystatin (Mycostatin) 100,000 units/mL.

GI upset, oral irritation


Continue use for at least 48 h after clinical cure.


Keep in mouth as long as possible before swallowing.

Infants: 1 mL each side of mouth


Adults: 2-3 mL each side of mouth


Oral Agents


griseofulvin (Grifulvin V)

Headaches, nausea, vomiting, diarrhea, photosensitivity

Pregnancy


Patients with porphyria or hepatic failure

Ultramicrosize particle increases absorption.


Prescribe with caution to patients who are sensitive to penicillin.


Drug is most effective when taken with a high-fat meal.


Drug is well tolerated in young children.


Monitor complete blood count and LFT with long-term use. Drug use may aggravate lupus erythematosus.


Use with alcohol produces antabuse-like effects.


Drug interactions: antagonizes oral contraceptives and warfarin and is antagonized by barbiturates

Microsize:


Adult 500-1,000 mg


Child 10-15 mg/kg/d


Ultramicrosize:


Adult: 330-660 mg


Child: 10 g/kg/d


ketoconazole (Nizoral) 200 mg/d

Nausea, vomiting, abdominal pain, urticaria, pruritus

Do not use with other drugs metabolized by CYP3A.

Not recommended in children


itraconazole (Sporanox) 200 mg/d

GI upset, rash, fatigue, headache, dizziness, edema

Do not use with other drugs metabolized by CYP3A

Not recommended in children


May use pulse dosing


Remains in nails for 4-5 mo


Ingestion of food increases absorption.


terbinafine (Lamisil) 62.5-250 mg/d

GI disturbance, LFT abnormalities, urticaria, pruritus

Liver or renal disease

Not recommended in children


fluconazole (Diflucan)

GI disturbance, headache, rash, hepatotoxicity


Decrease dose if creatinine clearance <50 mL/min.


Drug interactions: potentiates warfarin, theophylline, oral hypoglycemics.


May increase serum levels of phenytoin, cyclosporine.


Thiazides increase fluconazole levels.


May decrease effect of oral contraceptives

Adults: 100-200 mg/d


Children: 3-6 mg/kg/d


CYP3A, cytochrome P-450 enzyme 3A; GI, gastrointestinal; LFT, liver function tests; OTC, over the counter.

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Nov 11, 2018 | Posted by in PHARMACY | Comments Off on Fungal Infections of the Skin

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