Onychomycosis is the fungal infection of the nail plate and/or nail bed by dermatophytes, yeasts and non-dermatophytes molds. Dermatophytic onychomycosis is also known as tinea unguium. Onychomycosis is a common disease of dermatology that takes 50% of all nail diseases and 10% of skin infections1.
Dermatophytes are the most frequently seen pathogens of onychomycosis. These keratinophilic fungi can penetrate the nail plate and dissolve the keratin. The nail lacks cellular immune mechanism and is thus susceptible to fungal infections. Immunocompromised state, traumatized nail, concomitant tinea pedis and occlusive shoes are risk factors of onychomycosis1.
The infected nail plate shows opacity, thickening, detachment, discoloration, dystrophy, increased subungual scaling, rough surface. Onychomycosis can manifest 6 clinical patterns:
1. superficial white onychomycosis: the infection usually begins at the superficial layer of the nail plate and is restricted at the surface. The nail plate exhibits white opacity, plaque or grooves;
2. distal and lateral subungual onychomycosis: the infection begins at the distal and lateral end of the stratum corneum and extends to the nail bed. The free edge of the nail plate is raised and detached from the nail bed;
3. proximal subungual onychomycosis: the fungi invade from the proximal stratum corneum and appears as white plaque, which is restricted at the lunula of the nail at the beginning. The plaque can move to the distal as the nail plate grows;
4. endonyx onychomycosis: the defect is restricted inside the nail plate and does not affect the subungual area. The nail plate turns white or greyish-white without significant thickening or atrophy;
5. total dystrophic onychomycosis: if the onychomycosis continues to progress, the whole nail may be involved, where the nail plate is almost completely destroyed. Thickening of nail bed can be present;
6. Candidal onychia and paronychia: chronic inflammation of the proximal nail folds, often concomitant with paronychia. Detachment and thickening of the nail can be present.
Topical antifungal treatment is only applicable when <50% distal nail plate is infected, nail matrix is not affected and the number of involved nails is less than 4. However, the efficacy of topical treatment is limited due to the poor diffusion of the drug into the whole nail. Except the previous situations, one can choose systemic antifungal treatment. The treatment course for toenail onychomycosis is longer than that for fingernail onychomycosis1. Clinical efficacy can be proved when the new nail fully grows after treatment2.
1.  中国甲真菌病诊疗指南(2015年版)[J].中国真菌学杂志,2015,10(02):118-125.
2.  Package insert of Sporanox.