Background Superficial white onychomycosis (SWO) is a distinct pattern of fungal nail invasion, which is usually treated with topical antifungals.
Objective This paper presents a case of SWO with deep penetration and records other similar cases.
Methods The clues to deep invasion of the nail plate are twofold: an inability to clear the discoloration by scraping the nail and a clinical involvement of the nail plate in the proximal nailfold area. Histology of the nail keratin will confirm deep penetration beyond the superficial layers of the nail plate.
Results In the light of this finding the authors propose a further subdivision of SWO to reflect previously unrecognized variants with therapeutic implications into: (i) the classical SWO type; (ii) the dual invasion of the nail plate, superficial and ventral; and (iii) the pseudo-SWO with deep fungal invasion of the nail plate.
Conclusions This subdivision of SWO allows the clinician to treat the patient appropriately using topical antifungals when the disease is restricted to the dorsum of the nail. Systemic drugs either in isolation or in combination with topical treatment are mandatory when deep penetration or ventral fungal invasion are observed.