Onychomycosis: Clinical Aspects

Abstract

There are five types of onychomycosis based on pathogen mode of entry and clinical presentation: (1) distal and lateral subungual onychomycosis, (2) superficial onychomycosis, (3) proximal subungual onychomycosis, (4) endonyx onychomycosis, and (5) total dystrophic onychomycosis. Distal and lateral subungual onychomycosis is the most common type with infection starting in the hyponychium and distal or lateral nail bed and travelling proximally. This type has three main clinical features: subungual hyperkeratosis, onycholysis, and paronychia, albeit paronychia is uncommon. Superficial onychomycosis has two subtypes: superficial white onychomycosis and the rare superficial black onychomycosis (brown-black pigmentation known as fungal melanonychia). In both types, infection begins in the nail plate and then moves to the nail bed and hyponychium, with spots of discoloration that may gradually cover the whole nail plate. Proximal subungual onychomycosis is rare and begins in the stratum corneum, infecting the proximal nail plate and lunula. The infection moves distally and generally remains in the deeper layers of the nail. Endonyx onychomycosis also begins in the hyponychium; however, the hyponychium remains free of hyphae and the pathogen does not infect the nail bed or cause subungual hyperkeratosis or onycholysis. Instead, the pathogen infects the keratin, resulting in milky-white patches and lamellar splitting. Total dystrophic onychomycosis may be secondary or primary. Secondary total dystrophic onychomycosis is the complete progression of any of the previous types of onychomycosis. This presents with a crumbling nail plate and complete dystrophy. Primary infection occurs in immunocompromised patients and impacts all parts of the nail, often with swelling of the digits.