Onycomycosis (definition) is caused by dermatophytes fungi, also known as tinea unguium. The condition of the nail can also be caused by non-dermatophyte molds, and yeasts. It is a fungal infection affecting the nail.
This condition is usually seen in men more frequently than women. It is commonly associated with tinea pedis, concurrently. Onycomycosis will usually affect the toenails more commonly than the finger nails. If a fingernail infection occurs, it is usually in parallel with a toenail infection. There are three classifications of onychomycosis, each differing in the pattern of invasion: distal lateral subungual, proximal subungual, as well as superficial white.
DLSO, or distal lateral subungual onychomycosis, is the most common form and it will begin with the invasion of fungus in the hyponichium (distal portion of the nail). In many western nations, DLSO is common due mainly to Trichophyton rubrum.
Fungal invasion which is a result at the dorsal nail superficially is known as SWO, or superficial white onychomycosis. This condition is typically caused by T. rubrum, or T. mentagrophytes. This can be seen in HIV patients as well as those with immune deficiencies.
Another form of invasion known as PSO, or proximal subungual onychomycosis, will be seen in the proximal nail fold. This condition is typically caused by T. rubrum, in the absences of paronychia.
In samples of infected nails, sometimes Candida is seen. Usually, this is a result of a secondary infection in the nail. It is not usually thought of as the main culprit, or primary pathogen. Candida is commonly seen with chronic cases of paronychia. If Candida is the primary invasion, then it will typically be related to the patient having chronic mucocutaneous candidiasis.
If a patient’s immune system has been compromised, SWO and PSO are commonly reported. Increasing numbers of patients with SWO and PSO are seen in states which have higher numbers of HIV infection as well as compromised immune systems.