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Superficial Fungal Infections

Chapter 225 | Part 5: Infectious Diseases · Part 5 – Infectious Diseases: Fungal · Chapter 225

Key Clinical Points

  1. Malassezia species cause tinea versicolor, folliculitis, and seborrheic dermatitis without invading below the stratum corneum.
  2. Dermatophytes (Trichophyton, Microsporum, Epidermophyton) infect ~1 billion people globally; IL-17 responses restrict infections which occur more often in males.
  3. Candida albicans is most common for mucocutaneous candidiasis; C. auris is multidrug-resistant with propensity for long-term colonization.
  4. Sporothrix schenckii complex causes lymphocutaneous sporotrichosis with sequential lesions along lymphatic channels.
  5. Terbinafine 250 mg/day for 1-2 weeks is first-line for extensive tinea; itraconazole 200 mg/day for 3 months as an alternative.
  6. SSKI (40-50 drops TID) is a low-cost option for lymphocutaneous sporotrichosis.
  7. KOH microscopy showing hyphae confirms dermatophyte infections; culture is indicated for outbreaks or treatment failure.
  8. Tinea capitis most common in 3-7 year olds with scaly patches and broken hair shafts.
  9. Onychomycosis more prevalent in toenails; nail thickening, discoloration, and onycholysis are hallmarks.
  10. Ibrexafungerp (β-glucan inhibitor) and oteseconazole are newer VVC treatments with specific contraindications regarding reproductive potential.

1. DEFINITION & CLASSIFICATION

• Definition (Harrison's 22e): Superficial fungal infections are caused by molds and yeasts that do not invade deeper tissues but rather cause disease merely by inhabiting the superficial layers of skin, hair follicles, and nails.

• Classification: ◦ Malassezia infections: tinea versicolor (pityriasis versicolor), folliculitis, seborrheic dermatitis ◦ Dermatophyte infections: ringworm (tinea capitis, corporis, cruris, pedis, unguium/onychomycosis) ◦ Mucocutaneous Candida infections: oral thrush, esophageal candidiasis, vulvovaginal candidiasis (VVC), skin candidiasis ◦ Sporotrichosis: cutaneous, lymphocutaneous, osteoarticular, pulmonary, disseminated forms

• Terminology: ◦ Ringworm: Misnomer as no worms are involved. ◦ Tinea: Latin for "worm"; describes the serpentine nature of skin lesions. ◦ Specificity: Tinea capitis (head), tinea pedis (feet), tinea corporis (body), tinea cruris (crotch), and tinea unguium (nails; more often termed onychomycosis).

2. EPIDEMIOLOGY

• Global Impact: Dermatophyte infections affect ~1 billion people worldwide.

• Sporotrichosis: Primarily affects individuals involved in outdoor activities (landscaping, gardening, tree farming).

• Demographic Distribution: ◦ Tinea capitis: 3-7 year olds. ◦ Tinea cruris: Males only. ◦ Onychomycosis: Older adults, patients with vascular disease, and diabetes mellitus. ◦ Osteoarticular sporotrichosis: Middle-aged men with alcohol abuse. ◦ Disseminated sporotrichosis: Immunocompromised patients (especially AIDS).

3. ETIOLOGY & PATHOPHYSIOLOGY

• Malassezia Species: ◦ Agents: M. furfur and M. pachydermatis. ◦ Pathogenesis: Lipophilic yeasts inhabiting stratum corneum of sebaceous gland-rich areas; do not invade below stratum corneum. ◦ Immune Control: IL-17 signaling controls Malassezia in the skin. ◦ Rare Complication: Fungemia can occur in neonates on parenteral lipid nutrition.

• Dermatophyte Species: ◦ Genera: Trichophyton, Microsporum, Epidermophyton. ◦ Transmission: Not part of normal flora; spread via person-to-person contact, fomites, or soil. ◦ Pathology: Characteristic ring shape from outward growth in stratum corneum; symptoms caused by inflammatory reaction to fungal antigens.

• Candida Species: ◦ Common: C. albicans (commensal in oral, GI, and genitourinary tracts). ◦ C. auris: Multidrug-resistant with propensity for colonization. ◦ Immune Control: IL-17-producing lymphoid cells mediate control.

• Sporothrix Species: ◦ S. schenckii complex (6 species); S. brasiliensis linked to Brazilian outbreaks in cats. ◦ Environment: Found in sphagnum moss, decaying vegetation, and soil. ◦ Infection: Follows traumatic conidial inoculation.

4. CLINICAL FEATURES

• Malassezia Infections: ◦ Tinea versicolor: Hypo/hyperpigmented scaly patches on trunk. ◦ Folliculitis: Erythematous papules on back/chest. ◦ Seborrheic dermatitis: Erythematous, pruritic lesions in sebaceous areas.

• Dermatophyte Infections: ◦ Tinea capitis: Scaly patches with broken hair shafts (common in children). ◦ Tinea corporis: Annular, pruritic plaques with central clearing. ◦ Tinea cruris: Erythematous, pustular rash in groin area. ◦ Onychomycosis: Thickened, discolored nails with onycholysis.

• Sporotrichosis: ◦ Lymphocutaneous: Sequential nodules along lymphatic channels. ◦ Osteoarticular: Monoarticular synovitis (common in alcoholics). ◦ Pulmonary: Cavitary pneumonia resembling tuberculosis. ◦ Disseminated: Multiple ulcerated skin lesions with visceral spread.

• Candida Mucocutaneous: ◦ Oral thrush: White plaques on mucosa, removable by scraping. ◦ VVC: Pruritus, burning, and curd-like discharge. ◦ Skin candidiasis: Erythematous plaques with satellite lesions.

5. DIFFERENTIAL DIAGNOSIS

• Tinea Versicolor: Vitiligo (non-scaly, depigmented patches).

• Tinea Corporis: Contact dermatitis, Psoriasis, Eczema.

• Tinea Cruris: Intertriginous candidiasis, Erythrasma, Psoriasis.

• Onychomycosis: Psoriasis (associated with skin lesions).

• Sporotrichosis: Nocardiosis (N. brasiliensis), Tularemia, Mycobacterium marinum infection, Leishmaniasis.

6. DIAGNOSTIC APPROACH

  1. Clinical Examination: Identify characteristic lesions based on morphology and distribution.
  2. KOH Microscopy: Perform on lesion edge scrapings to identify budding yeast (Malassezia) or hyphae (dermatophytes).
  3. Culture: ◦ Sabouraud's agar for dermatophytes. ◦ Add olive oil to media for Malassezia. ◦ Culture is specifically indicated for outbreaks or cases of treatment failure.
  4. Biopsy: Utilized for differential diagnosis (e.g., distinguishing thrush from leukoplakia, or identifying psoriasis).

7. MANAGEMENT & TREATMENT

  1. Malassezia Infections: • Topical: Selenium sulfide shampoo; ketoconazole cream (2 weeks). • Seborrheic dermatitis: Mild topical steroids. • Extensive disease: Oral itraconazole or fluconazole 200 mg/day for 5-7 days. • Fungemia: Amphotericin B or voriconazole + catheter removal.

  2. Dermatophyte Infections: • Topical: Azoles or terbinafine (lotions/sprays preferred). • Tinea cruris: Keep area dry. • Extensive disease: Oral itraconazole or terbinafine. • Onychomycosis: Efinaconazole topical solution ×1 year; itraconazole or terbinafine (accumulate in nail plate).

  3. Sporotrichosis: • Cutaneous, lymphocutaneous: Itraconazole 200 mg/day until 2-4 weeks after lesions resolve; SSKI (increasing doses); Terbinafine 500 mg twice daily. • Pulmonary: Lipid AmB initially, then itraconazole ×12 months. • Disseminated: Lipid AmB ×4-6 weeks + itraconazole maintenance. • AIDS patients: Continue itraconazole until CD4 >200/μL for ≥12 months.

  4. Candida Mucocutaneous Infections: • Mild oral thrush: Nystatin suspension, clotrimazole troches. • Moderate/severe: Systemic azoles (fluconazole). • VVC: Topical/oral azoles; newer options include ibrexafungerp and oteseconazole (contraindicated in patients with reproductive potential).

  5. Drug-Specific Considerations: • Itraconazole: Requires food and gastric acid; SUBA formulation improves bioavailability; monitor for hepatotoxicity, hypokalemia, hypertension, edema. • SSKI: Increase dosage weekly up to 40-50 drops TID. • Oteseconazole: Contraindicated due to fetal ocular toxicity.

8. PROGNOSIS & COMPLICATIONS

• Malassezia Prognosis: Generally benign; relapses common with inadequate treatment.

• Dermatophyte Prognosis: Excellent with appropriate therapy; relapses in 25-30% of onychomycosis cases.

9. SPECIAL CONSIDERATIONS

• Immunocompromised Patients: ◦ Higher risk of disseminated infections. ◦ Prolonged treatment durations required. ◦ Monitor for drug interactions and toxicity.

• Neonates: ◦ Malassezia fungemia occurs in neonates on parenteral lipid nutrition. ◦ Treatment: Amphotericin B or voriconazole; discontinue lipid infusions.

• Healthcare Settings: ◦ C. auris outbreaks require strict infection control measures. ◦ Environmental decontamination critical for persistent colonization.

10. KEY PEARLS & CLINICAL TRAPS

• Diagnostic Clues: ◦ Tinea versicolor: Distinguish from non-scaly vitiligo. ◦ Onychomycosis: Identify nail thickening + onycholysis vs. psoriasis with skin lesions.

• Clinical Traps: ◦ Misdiagnosis of sporotrichosis as nocardiosis or leishmaniasis. ◦ Overlooking C. auris colonization in healthcare settings.

Reference Tables

TABLE 225-1 Suggested Oral Treatment for Extensive Tinea Infections and Onychomycosis

Harrison's 22e, p.1724

ANTIFUNGAL
AGENT		 SUGGESTED
DOSAGE		 COMMENTS
Extensive Tinea Infection
Terbinafine 250 mg/day for
1–2 weeks		 Adverse reactions minimal with short
treatment period
200 mg/day for
1–2 weeks
Onychomycosis
Terbinafine 250 mg/day for
3 months		 Slightly superior to itraconazole; monitor
for hepatotoxicity
200 mg/day for
3 months or 200
twice daily for
1 week each month
for 3 months

TABLE 225-2 Suggested Treatment for Sporotrichosis DISEASE Cutaneous, lymphocutaneous Pulmonary, osteoarticular…

Harrison's 22e, p.1724

DISEASE FIRST-LINE
THERAPY		 ALTERNATIVES/COMMENTS
Cutaneous,
lymphocutaneous		 Itraconazole, 200 mg/
day until 2–4 weeks
after lesions resolve		 SSKI, increasing dosesa
Terbinafine, 500 mg twice daily
Itraconazole,
200 mg twice daily
for 12 months
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 is >200/μL
for ≥12 months