Superficial Fungal Infections¶
Chapter 225 | Part 5: Infectious Diseases
KEY CLINICAL POINTS¶
- Malassezia species cause tinea versicolor, folliculitis, and seborrheic dermatitis; treatment includes selenium sulfide shampoo and terbinafine
- Dermatophytes (Trichophyton, Microsporum, Epidermophyton) cause ringworm (tinea) and onychomycosis; treatment options include terbinafine, itraconazole, and efinaconazole
- Candida albicans is the primary cause of mucocutaneous candidiasis; antifungals like nystatin, clotrimazole, and azoles are used
- Sporotrichosis is caused by Sporothrix schenckii complex; treatment includes itraconazole, terbinafine, and potassium iodide
- Diagnosis relies on potassium hydroxide mounts, culture, and clinical appearance; treatment duration varies by infection type
1. DEFINITION & OVERVIEW¶
Superficial fungal infections involve the skin, hair, nails, and mucous membranes. These infections are caused by dermatophytes, Malassezia, Candida, and Sporothrix species. They typically do not invade deeper tissues but cause disease through superficial colonization. Common presentations include tinea (ringworm), onychomycosis (nail infections), and candidiasis.
Table 225-1: Suggested Oral Treatment for Extensive Tinea Infections and Onychomycosis¶
| ANTIFUNGAL AGENT | SUGGESTED DOSAGE | COMMENTS |
|---|---|---|
| Terbinafine | 250 mg/day for 1–2 weeks | Adverse reactions minimal with short treatment period |
| Itraconazole | 200 mg/day for 1–2 weeks | Adverse reactions minimal with short treatment period except for drug interactions |
| Terbinafine | 250 mg/day for 3 months | Slightly superior to itraconazole; monitor for hepatotoxicity |
| Itraconazole | 200 mg/day for 3 months or 200 mg twice daily for 1 week each month for 3 months | Drug interactions frequent; monitor for hypokalemia, hypertension, edema; use with caution in patients with congestive heart failure |
Table 225-2: Suggested Treatment for Sporotrichosis¶
| DISEASE | FIRST-LINE THERAPY | ALTERNATIVES/COMMENTS |
|---|---|---|
| Cutaneous, lymphocutaneous | Itraconazole, 200 mg/day until 2–4 weeks after lesions resolve | SSKI, increasing dosagesa; Terbinafine, 500 mg twice daily |
| DISEASE | FIRST-LINE THERAPY | ALTERNATIVES/COMMENTS |
|---|---|---|
| Pulmonary, osteoarticular | Itraconazole, 200 mg twice daily until stable; then itraconazole for 12 months | Lipid AmBb for severe pulmonary disease until stable |
| Disseminated, central nervous system | Lipid AmBb for 4–6 weeks | Itraconazole, 200 mg twice daily after AmB for 12 months |
| Patients with AIDS | Itraconazole maintenance, 200 mg/day until CD4+ T cell count >200/mL for ‡12 months |
1.1 Clinical Spectrum¶
Infections range from benign superficial lesions (e.g., tinea versicolor) to more severe conditions like disseminated candidiasis. Malassezia infections are common in seborrheic areas, while dermatophytes cause cutaneous and nail infections. Sporotrichosis is a zoonotic infection often acquired from traumatic inoculation.
1.2 Diagnostic Approach¶
Diagnosis is primarily clinical with potassium hydroxide mounts, culture, and histopathology. Dermatophytes show hyphal elements, while Malassezia presents as budding yeast and short hyphae. Sporothrix species grow as molds on Sabouraud's agar.
2. EPIDEMIOLOGY¶
Malassezia infections are common in warm, moist areas and affect 10–20% of the population. Dermatophyte infections are globally prevalent, with ~1 billion people affected. Sporotrichosis is endemic in tropical and subtropical regions, with cats and armadillos as reservoirs. Candida infections are more common in immunocompromised hosts, including those with diabetes, HIV, or neutropenia.
2.1 Risk Factors¶
Malassezia: Obesity, seborrhea, immunosuppression. Dermatophytes: Warm climates, close contact with infected animals. Sporotrichosis: Outdoor work, cat exposure, immunosuppression. Candida: Diabetes, antibiotic use, immunosuppression.
2.2 Demographics¶
Tinea versicolor is common in adolescents and young adults. Onychomycosis is more prevalent in older adults. Sporotrichosis occurs in middle-aged men with alcohol abuse. Mucocutaneous candidiasis is seen in neonates and immunocompromised hosts.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Malassezia species are lipophilic yeasts that colonize sebaceous glands. Dermatophytes are keratinophilic fungi that invade keratinized structures. Sporothrix schenckii is a dimorphic fungus that grows as a mold in soil and decaying vegetation. Candida albicans is a commensal yeast that can invade mucosal surfaces under immunosuppressive conditions.
3.1 Immune Mechanisms¶
IL-17 signaling controls Malassezia and dermatophyte infections. Neutrophil recovery is critical for sporotrichosis outcomes. Candida infections are mediated by T17 cells and innate lymphoid cells.
3.2 Pathogenesis¶
Malassezia causes inflammation via IL-17 overproduction. Dermatophytes spread via keratin filaments. Sporothrix spreads via lymphatics, causing lymphocutaneous or disseminated disease.
4. CLINICAL FEATURES¶
Malassezia: Hypopigmented scaly patches, seborrheic dermatitis. Dermatophytes: Annular erythematous lesions (tinea corporis), nail thickening (onychomycosis). Sporotrichosis: Papule-ulcer progression along lymphatics, nodular lesions. Candida: Oral thrush, vulvovaginal discharge, nail invasion.
4.1 Complications¶
Disseminated candidiasis in immunocompromised hosts. Sporotrichosis dissemination in AIDS patients. Severe onychomycosis leading to nail loss.
4.2 Differential Diagnosis¶
Tinea vs. psoriasis, eczema, contact dermatitis. Sporotrichosis vs. nocardiosis, leishmaniasis, tuberculosis.
5. INVESTIGATIONS & DIAGNOSIS¶
Potassium hydroxide mounts for hyphal elements. Culture on Sabouraud's agar for dermatophytes and Sporothrix. Histopathology shows granulomatous inflammation with fungal elements. PCR and fungal cultures may be used for confirmation.
5.1 Diagnostic Criteria¶
Clinical appearance (ring-shaped lesions), KOH mount findings, culture confirmation. Sporotrichosis diagnosis requires fungal culture or PCR.
5.2 Imaging¶
MRI for CNS sporotrichosis. Ultrasound for deep fungal infections. Not routinely used for superficial infections.
6. MANAGEMENT & TREATMENT¶
Topical antifungals (selenium sulfide, ketoconazole) for Malassezia. Terbinafine, itraconazole, or efinaconazole for dermatophytes. Itraconazole or terbinafine for sporotrichosis. Systemic azoles for severe candidiasis. Long-term maintenance therapy for chronic infections.
6.1 Treatment Algorithms¶
- Mild tinea: topical therapy. 2. Severe tinea: oral terbinafine/itraconazole. 3. Sporotrichosis: itraconazole (first-line), potassium iodide. 4. Onychomycosis: terbinafine (3 months) or efinaconazole (year).
6.2 Monitoring¶
Liver function tests for azole therapy. Monitor for drug interactions (e.g., terbinafine with anticoagulants). Follow-up for relapses (especially tinea cruris/pedis).
7. PROGNOSIS & COMPLICATIONS¶
Superficial infections are generally benign with good prognosis. Disseminated candidiasis and sporotrichosis have high mortality in immunocompromised hosts. Chronic onychomycosis may lead to nail loss and reduced quality of life.
7.1 Prognostic Factors¶
Immune status, infection severity, adherence to treatment. Early intervention improves outcomes for sporotrichosis.
7.2 Long-Term Effects¶
Recurrence of tinea cruris/pedis, chronic nail dystrophy, and psychological impact from cosmetic lesions.
8. SPECIAL CONSIDERATIONS¶
Pregnancy: Avoid terbinafine; use topical treatments. Pediatrics: Malassezia infections are common in children. Elderly: Increased risk of onychomycosis and candidiasis. Immunocompromised: Monitor for disseminated infections.
8.1 Drug Interactions¶
Terbinafine interacts with anticoagulants and cyclosporine. Itraconazole interacts with CYP3A4 inhibitors.
8.2 Pregnancy¶
Avoid terbinafine in first trimester. Use topical antifungals for Malassezia. Monitor for candidiasis in neonates.
9. KEY POINTS & CLINICAL PEARLS¶
- Malassezia infections are treated with selenium sulfide shampoo and terbinafine.
- Dermatophytes require oral antifungals (terbinafine, itraconazole) for extensive infections.
- Sporotrichosis is diagnosed by fungal culture and treated with itraconazole or potassium iodide.
- Onychomycosis is managed with terbinafine (3 months) or efinaconazole (year).
- Monitor for drug interactions and liver toxicity with azole therapy.
- Early treatment prevents dissemination in immunocompromised hosts.