"Endonyx" onychomycosis: a new modality of nail invasion by dermatophytes

Three patients with onychomycosis due to Trichophyton soudanense with an "endonyx" type of nail invasion are presented. Endonyx onychomycosis is clinically characterized by a diffuse milky-white discolouration of the affected nail, in the absence of nail bed hyperkeratosis or onycholysis. Nail plate surface and nail thickness are normal. The pathology shows a contrast between the great number of fungal hyphae visible in the nail plate and the absence of fungal elements in the nail bed. The nail bed does not show inflammatory changes or hyperkeratosis and adheres strictly to the lowermost layers of the nail plate. The hyponychium is normal and does not contain hyphae. The endonyx pattern of nail infection appears to be specific to T. soudanense nail invasion and may possibly reflect the high affinity of T. soudanense to hard keratins.