Onychomycosis Clinical Considerations and Recommendations

Mickey Hart, PharmD Candidate 2015; Lynne Fehrenbacher, PharmD, BCPS-AQ ID


US Pharmacist 

In This Article


Onychomycosis of the toenails may be clinically characterized by thickening of the toenails, onycholysis (separation of the nail plate from the nail bed), subungual hyperkeratosis (buildup of debris in the space created by onycholysis), and nail discoloration (usually yellow-brown or white).[1,4] Only about half of nail dystrophy cases are caused by fungi, making appropriate diagnostic technique necessary to rule out disease states with similar presentations (e.g., psoriasis, nail trauma).[4] Currently, the most efficient screening test for onychomycosis is direct microscopy of a potassium hydroxide–prepared nail specimen; however, this technique has a false-negative rate of 5% to 15% and lacks differentiation between fungal pathogens.[4] Fungal pathogens can only be identified by performing in vitro laboratory culture, which facilitates also antifungal susceptibility testing. Unfortunately, this technique suffers from a false-negative rate of nearly 50%.[4] Due to their limitations, direct microscopy and in vitro laboratory culture of nail material should optimally be used together when diagnosing suspected onychomycosis. Despite this recommendation, onychomycosis is often treated empirically based on clinical presentation.