Fifth toenail clinical response to systemic antifungal therapy is not a marker of successful therapy for other toenails with onychomycosis

[[[ Background: ]]] Onychodystrophy is a major manifestation of onychomycosis. However, nail trauma may also result in onychodystrophy. The fifth toenail, due to its location, suffers repeated friction/pressure trauma from shoes. [[[ Objective: ]]] To test the hypothesis that treatment failure of fifth toenail onychomycosis is not a marker of treatment failure of other toenails with onychomycosis. [[[ Methods: ]]] Fifty patients who had fifth toenail deformity (with or without onychomycosis) and onychomycosis of the other toenails were treated with oral terbinafine, 250 mg/day, for 4 months. [[[ Results: ]]] Forty-three patients completed the study. Before the study, 26/43 (61%) had callus lateral to the fifth toe (suggesting mechanical pressure in that area). Twenty-one/43 (49%) of the fifth toenails had onychomycosis. At the end of the treatment period, only 4/21 (19%) of the fifth toenails (with initial onychomycosis), compared with 12/21 (57%) of the other toenails, were completely cured (CC). Out of the whole group (n=43), the clinical cure rate of the fifth toenail was 4/43 (9%) and for the other toenails, 20/43 (47%) (P<0.05). The mycological cure rates were 11/21 (52%) for the fifth toenail and 25/43 (58%) for the other toenails. Callus lateral to the fifth toe was associated with a poor clinical result (P<0.01). [[[ Conclusions: ]]] Clinical improvement of the fifth toenail after systemic antifungal therapy is less favourable and does not correspond with the clinical cure of the other toenails, mostly because of mechanical factors. Therefore, patients should be told to adjust their expectations as to the visual results of their antifungal treatment.