To have a better understanding of how fungal nail infection affects the nail, a general knowledge of the anatomy of the nail is helpful.

The nail, or nail unit, consists of the following parts:

 

1. The nail matrix is where nail cells multiply and keratinize (harden and form into nail material) before being incorporated into the fingernail or toenail.

Most of the matrix is not visible;
The matrix starts under the skin 5 mm below the nail fold (the area of the cuticle where the finger or toe skin meets the nail) and covers the area called the lunula, or half moon (the white half moon-shaped area at the bottom of the nail);
2. The cuticle is a fold of modified skin where the finger or toe meets the nail;
The cuticle protects the matrix from infection;
3. The nail plate is the nail itself;
4. The nail bed is the soft tissue underneath the nail, anchoring the nail plate;
The nail plate protects the nail bed.

 

What Are the Subtypes of Fungal Nail Infections?

1. Distal lateral subungual onychomycosis (DLSO) is the most common form of fungal nail infection.
In DLSO, the fungus generally spreads from the skin and invades the underside of the nail where the nail meets the nail bed.

Inflammation in these areas of the nail causes the symptoms of DLSO;

2. White superficial onychomycosis (WSO) is a rare infection caused by the fungi directly invading the surface of the nail plate and secondarily infecting the nail bed;

3. In proximal subungual onychomycosis (PSO), the least common subtype, the fungi invade the cuticle (the skin around the nail) and the nail fold and then penetrate the nail plate (fingernail or toenail);

4. Like DLSO, in endonyx onychomycosis (EO), the fungi reach the nail via the skin. Instead of infecting the nail bed, however, the fungi immediately invade the nail plate;

5. Fungal nail infection related to yeast (Candida) infection is a little different from fungal nail infection related to other fungal infections;

Candidal fungal nail infection has several characteristics:
Onycholysis describes the nail separating from the nail bed.
Chronic mucocutaneous disease (disease of mucous membrane and regular skin) involves the nail plate (fingernail or toenail) and eventually the nail fold (the skin fold behind the cuticle, where the nail meets the finger or toe);

 

6. Total dystrophic onychomycosis is not a distinct subtype of fungal nail infection;
Dystrophic onychomycosis is the term used to describe the most advanced form of any of the above subtypes, and it involves the entire nail unit;
Dystrophic onychomycosis may cause permanent scarring of the nail matrix.

 

What Causes a Fungal Nail Infection?

Fungal nail infection is caused by three main classes of organisms: fungi that infect hair, skin, and nails and feed on nail tissue, yeasts, and non dermatophyte molds.
All three classes cause the very similar early and chronic symptoms or appearances, so the visual appearance of the infection may not reveal which class is responsible for the infection.
Dermatophytes (including Epidermophyton, Microsporum, and Trichophyton species) are, by far, the most common causes of fungal nail infection worldwide.

Yeasts cause 8% of infections, and non dermatophyte molds cause 2% of fungal nail infections.

1. The dermatophyte Trichophyton rubrum is the most common fungus causing distal lateral subungual onychomycosis (DLSO) and proximal subungual onychomycosis (PSO).
2. The dermatophyte Trichophyton mentagrophytes commonly causes white superficial onychomycosis (WSO), and more rarely, WSO can be caused by species of non-dermatophyte molds.
3. The yeast Candida albicans is the most common cause of chronic mucocutaneous candidiasis (disease of mucous membrane and regular skin) of the nail.

 

 

How Do Health Care Professionals Diagnose a Fungal Nail Infection?

Fungal nail infection can be identified by it's appearance.
However, other conditions and infections can cause problems in the nails that look like fungal nail infection.
Fungal nail infection must be confirmed by laboratory tests before beginning treatment, because treatment is long, expensive, and does have some risks.

1. A sample of the nail can be examined under a microscope to detect fungi.
2. The nails must be clipped and cleaned with an alcohol swab to remove bacteria and dirt so the fungal structures can be more easily visualized with a microscope.
3. If proximal subungual onychomycosis (PSO) is suspected, the sample is taken from the underlying nail bed close to the lunula.
4. A piece of the nail surface is taken for examination if white superficial onychomycosis (WSO) is suspected.
5. To detect candidal fungal nail infection, the specialist should take a sample from the affected nail bed edges closest to the cuticle and sides of the nail.
6. If fungi are present in the infected nail, they can be seen through a microscope, but the exact type (species) cannot be determined by simply looking through a microscope.
To identify what exactly is causing fungal nail infection, a fungal culturing is used.

Using a fungal culture to identify the particular fungus is important because regular therapy may not work on non-dermatophyte molds.
1. The infected nail is scraped or clipped.
2. The scrapings or clippings are crushed and put into containers.

Any fungus in the samples can grow in the laboratory in these special containers.

This is true for most molds and yeast also.
3. The species of pathogen (usually a fungus) can be identified from the cultures grown in the lab by technicians trained to recognize the microscopic structures that are identifiers of the fungal species.