Most cases of onychomycosis are due to dermatophytes, and we discuss this entity separately under our general discussion of onychomycosis. However, Candida spp. also cause this condition, and there are enough differences to warrant a separate discussion. Onychomycosis due to dermatophytes occurs more frequently in toenails than in fingernails. Conversely, candidal onychomycosis more commonly affects the fingernails. Indeed, about 50% of cases of fingernail-related onychomycosis is caused by Candida spp.

In addition, most episodes of Candida onychomycosis begin as paronychial infections ("whitlow"). In other words, infection begins in the structures around the nail rather than in the nail itself. Again, the opposite is generally true of dermatophytic onychomycosis.

Patients with chronic mucocutaneous candidiasis (CMC) have a special propensity to suffer from candidal onychomycosis. However, they are usually affected by another type of onychomycosis called Candida granuloma.

Our knowledge of the true incidence of Candida onychomycosis is limited by the scarcity of data on this specific type of onychomycosis. In addition, many affected patients will see their general practitioner, while others may not even consult a physician but a manicurist.

An indirect estimation can be made using available data on onychomycosis. In the USA, a survey of 1,038 outpatients in a dermatology clinic demonstrated culture-proven onychomycosis in 8.7% of these patients [656]. Knowing that 10% of these cases were fingernail infections, and that Candida is responsible for half of these cases, we can estimate that around 0.4% of the population was affected by this entity.

Nevertheless, geographical variations on the frequency of this superficial fungal infection, either related to climate or other particular conditions, are very likely. In fact, a good example of this phenomenon is seen in Saudi Arabia. In that country, an exceptionally high incidence of Candida onychomycosis of the toenails has been described. It has been suggested that this phenomenon might be related to the Moslem religious practice of washing the feet five times a day [2311].

Candidal onychomycosis and Candida species. Candida albicans is the most frequent species causing candidal onychomycosis [702]. Among the non-albicans species, C. parapsilosis, C.krusei, and C. guillermondii are the most frequently seen species [702, 1672].

Candidal onychomycosis generally presents in one of these patterns of onychomycosis:

Proximal Subungual Infection
In this case, Candida spp. penetrate the nail plate after having affected the soft tissue around the nail. The soft tissues around the nail will appear red and edematous. Once the nail matrix is infected, transverse depressions, known as "Beau's lines" may become apparent in the nail plate. A progressive change of the nail form transforms the nail into a rough, irregular, convex and finally dystrophic nail [656].
Onycholysis
In this case, distal subungal hyperkeratosis produces a yellowish-gray mass that lifts off the nail plate [656]. This separation, or lysis, of the nail is basis for the name of this form of candidal onychomycosis.
Candida granuloma
Unique to patients with CMC, in this severe form of onychomycosis, Candida invades the nail directly and affects the complete thickness. Advanced cases with swelling of the lateral and proximal nail folds may end up causing a digit deformity called "chicken drumstick" [656].

The diagnostic strategies for candidal onychomycosis are the same as those for dermatophytic onychomycosis.

The therapeutic strategies for candidal onychomycosis are the same as those for dermatophytic onychomycosis.

References

656. Elewski, B. E. 1998. Onychomycosis: Pathogenesis, diagnosis, and management. Clin. Microbiol. Rev. 11:415-429.

702. Faergemann, J. 1996. The role of yeasts in onychomycosis. Mycoses. 39:223-224.

1672. Odds, F. C. 1988. Candida and Candidosis, 2nd ed. Bailliere Tindall, London.

2311. Venugopal, P. V., and T. V. Venugopal. 1992. Superficial mycoses in Saudi Arabia. Australas J Dermatol. 33:45-8.