Malassezia furfur as a Cause of Onychomycosis
Malassezia furfur can rarely cause onychomycosis, but it is not a common etiologic agent and is generally considered an opportunistic pathogen in nail infections. 1, 2
Etiology of Onychomycosis
Onychomycosis is primarily caused by:
- Dermatophytes (most common causative agents), particularly Trichophyton rubrum and Trichophyton mentagrophytes 3
- Candida species (especially in fingernail infections) 3
- Non-dermatophyte molds (NDMs) such as Scopulariopsis brevicaulis, Fusarium, and Aspergillus species 4
Malassezia furfur and Nail Infections
Malassezia furfur is:
- Primarily known as a lipophilic yeast that causes skin conditions like pityriasis versicolor 5
- Rarely reported as a causative agent of onychomycosis 5
- Documented in isolated case reports of nail infections 1, 2
Evidence for M. furfur in Onychomycosis
- A Brazilian study found M. furfur in the nails of 14 out of 370 patients with onychomycosis 1
- A case report documented M. furfur as an etiologic agent rather than a colonizer in a child with onychomycosis, with successful treatment using ketoconazole 2
Clinical Patterns of Onychomycosis
Onychomycosis presents in five main clinical patterns:
- Distal and lateral subungual onychomycosis (DLSO) - most common pattern 3
- Superficial white onychomycosis (SWO) 3
- Proximal subungual onychomycosis (PSO) 3
- Endonyx onychomycosis 3
- Total dystrophic onychomycosis (TDO) 3
Risk Factors for Onychomycosis
- Increasing age (20% prevalence in those over 60 years, up to 50% in those over 70) 3
- Male gender 3
- Reduced peripheral circulation 3
- Immunosuppression (HIV infection, transplant recipients) 3
- Diabetes mellitus 3
- Genetic predisposition 3
- Previous nail trauma 3
- Hyperhidrosis 3
Diagnostic Considerations
When suspecting Malassezia onychomycosis:
- Direct microscopy with KOH preparation to visualize budding yeast cells 2
- Culture on lipid-supplemented media (as Malassezia requires lipids for growth) 2
- Histopathology with H&E and PAS staining to demonstrate fungal invasion of nail keratin 2
- Rule out more common causes of onychomycosis (dermatophytes, Candida) 6
Clinical Implications
- It's important to differentiate between true infection and colonization when Malassezia is isolated from nail specimens 2
- Multiple positive cultures and demonstration of invasion into nail keratin suggest a true infection rather than contamination 2
- Treatment with azole antifungals (particularly ketoconazole) has shown efficacy in documented cases 2
Conclusion
While Malassezia furfur can cause onychomycosis in rare instances, it should be considered an uncommon opportunistic pathogen in nail infections. Proper diagnostic workup is essential to establish its etiologic role versus mere colonization when isolated from nail specimens.