Recent Advances in Onychomycosis Epidemiology, Diagnosis, and Risk Factors

Conclusions

• Distal lateral subungual onychomycosis is the most common clinical form of toenail infection, while other forms such as superficial white, endonyx, and total dystrophic disease are less frequent.
• Endonyx onychomycosis is a distinct pattern where fungus invades the nail plate without nail-bed inflammation, hyperkeratosis, or onycholysis, and it appears to be reported mainly in Asia and Africa.
• Overall dermatophyte onychomycosis has a global prevalence of about 4%, with higher risk in congregate settings and in older adults.
• In U.S. molecular/pathology-based data, non-dermatophyte molds are more common in women than men, occurring at roughly twice the rate in females.
• The main U.S. non-dermatophyte mold pathogens are Aspergillus and Fusarium, with other molds such as Neoscytalidium also contributing.
• Trichophyton mentagrophytes is a genetically diverse complex, and certain genotypes are associated with onychomycosis, tinea pedis, sexual transmission, and terbinafine resistance.
• Mixed infections are common, so finding a dermatophyte does not exclude a concurrent non-dermatophyte mold that may cause treatment failure if not identified.
• Onychomycosis is more common in special populations such as patients with diabetes, immunosuppression, renal transplant, HIV, lupus, chronic venous disease, and some older adults.
• Pediatric onychomycosis occurs less often than adult disease, but clinicians still need to consider it in children.
• Onychomycosis should not always be considered purely cosmetic because invasive or disseminated fungal disease can occur in severely immunocompromised patients, especially with Fusarium.
• Patients with onychomycosis who are scheduled for transplantation should be treated before or at the time of transplant to reduce risk.
• Accurate diagnostic testing, including PCR and histopathology, is essential to confirm the diagnosis and identify the causative species so therapy can be appropriately targeted.
• Despite the importance of testing, many cases are still under-tested, so improved diagnostic confirmation is needed in routine practice.