Onychomycosis: is it possible to increase the cure rate?

Onychomycosis represent about 50% of nails disorders in the world with a very variable prevalence depending of the countries considered. Dermatophytes, non-dermatophyte molds and Candida sp. are the main causing agents. A rapid and accurate diagnosis is essential in order to give an adequate treatment to the patient. Generally, a combination of microscopy and culture is used for laboratory diagnosis. However, microscopy does not always allow the distinction between yeasts or filamentous fungi, culture takes generally about a week before identification and the result is compromised if there is contamination by not relevant fungi. Therefore commercially available PCR-based methods have been developed in order to provide a rapid and accurate identification of dermatophytes and yeasts in nails samples. Combination of microscopy and PCR may provide a rapid and specific diagnosis in 2 working days. However this methodology is still not widely used by laboratories because of the high cost. Furthermore, this technology can detect DNA from dead fungi and therefore is not suitable for assessment of treatment efficacy.
Onychomycosis therapy depends on different factors such as the causative agent, the number of nails and degree of nail involvement, the type of onychomycosis, potential drug interactions or drug intolerance and a failure to previous treatments. Oral and topical antifungals are mostly used separately or in combination. Oral therapy includes azoles (itraconazole, fluconazole) and/or allylamine (terbinafin), this latter being the most frequently prescribed antifungal for treatment of onychomycosis in North America and Europe. Topical amorolfine and ciclopirox formulations can be used alone in mild cases or in case of intolerance to oral antifungals. However, one of the biggest problems of therapy for onychomycosis is the high frequency of relapse which concerns about 20 to 40% of the patients treated by oral antifungals. Different strategies have been developed to overcome this problem amongst which are: optimization of the dosing regimens (continuous vs pulse therapy) or therapy duration, combination therapy (nail debridement + antifungals, oral + topical drugs, 2 oral drugs), improving drug delivery (use of physical or chemical enhancers, and modification of the pharmacological formulation for increasing drug uptake). Some strategies such as combination therapy (oral + topical) have demonstrated enhanced efficacy and should be recommended in case of poor efficacy of the initial treatment or in case of extended infection. Prophylactic topical therapy implemented after completion of oral treatment has been shown to delay relapse. Preventive measures such as treatment of concurrent tinea pedis and/or infected family members and regular cleaning of bathroom and shower floors can help to reduce the risk of reinfection particularly when a dermatophyte is the causative agent.
In conclusion, treatment for onychomycosis is associated with frequent relapse. Consequently, follow-up is mandatory and combination therapy can be necessary in case of relapse or resistance to treatment. Patients should also be aware of the preventive hygiene measures to apply in order to decrease the risk of reinfection. New strategies improving treatment efficacy are promising but their efficacy have still to be demonstrated in comparative clinical trials before their implementation in therapy.