Toenails and Mycosis: Treatment and Prevention Strategies

In laminae that are compact and healthy (not damaged by disease or trauma), onychomycosis of the toenail is a rare occurrence. However, diagnoses of mycosis are as frequent as they are wrong, meaning many patients undergo long, expensive treatment plans that do not address the problem.
The cause of this frequent misdiagnosis is the general lack of understanding of nail mycoses. In addition, some species of fungi found in the toenails do not cause any disorders and are not the cause of the nail pathology, so do not respond when treated with antifungals.

Onychomycosis describes a nail that has been invaded by fungal elements

Classifying fungal elements is complex and, even today, there are no definitive classifications. However, in dermatology, fungi fall into one of three categories: Dermatophytes are keratinophilic fungi because they feed on keratin, which is the main protein of the stratum corneum, hair and nails.

As such, this group of fungi can affect only the surface of the skin and hair follicles. Skin and adnexal infections caused by dermatophytes are called tinea, and are mainly attributable to trichophyton and mentagrophyte species. Yeasts are unicellular microorganisms similar to bacteria, the most common of which is candida. They can be found at random on the skin where they do not cause any type of pathology. However, in moist environments such as the mouth or the vagina, yeasts can cause conditions such as oral thrush or vaginal candidiasis, respectively. Molds can cause severe systemic infections in immunocompromised individuals. They are often found on the skin without causing any type of pathology. Among the most frequently isolated molds are scopulariopsis brevicaulis, fusarium and aspergillus.

Various forms of onychomycosis

Lateral distal subungual onychomycosis

It’s the most frequent form of toenail fungus, lateral distal subungual onychomycosis, it arises from a fungal infection between the toes, which then spreads to the foot and then to the nail bed. Inflammation is present.

Proximal subungual onychomycosis (PSO)

It is the rarest form of onychomycosis, in which colonization of the nail matrix occurs through the proximal fold and is followed by invasion of the proximal part of the lamina.

White superficial onychomycosis (WSO)

A rare form of onychomycosis, WSO is caused by the direct invasion of the nail plate’s surface. The proximal portion appears white and the surface of the lamina is intact. WSO is present in about 90% of immunocompromised patients.

Endonyx (EO)

EO is a variant of distal lateral subungual onychomycosis. From the skin, fungal invasion is directed at the level of the nail plate.

While onychomycosis may appear common, it is actually a very rare occurrence and is often confused for other nail conditions at the point of diagnosis.

Why is onychomycosis so often misdiagnosed?

The main reason for misdiagnosis and, therefore, mistreatment lies in confusing onychomycosis with other, much more common nail diseases such as nail psoriasis or onychodystrophy. In addition, medical terminology needs to be updated to allow for more accurate diagnosis.

If yeast or mold is found on the nail, does it automatically mean onychomycosis is present?

The answer is NO. Yeast or mold can only be found on the nail plate once it has already been damaged or disrupted by another pathology such as psoriasis or onychodystrophy. They are not the original cause of nail damage, but are the original pathology that has allowed the molds or yeasts to establish themselves. Cases of yeast or mold on the nail are, therefore, a contamination, not a parasitism of the nail. In terms of treatment, if the contaminated nail is treated with local or systemic antifungals, the yeast or mold may well be eliminated but the nail and the damage remain. This treatment failure is widespread in cases of yeast and mold on the nail.

Keratinophilic Dermatophytes = Onychomycosis

Onychomycosis only applies in the rare cases where keratinophilic dermatophytes are present. These dermatophytes break down keratins which leads to nail damage or destruction. While using topical or systemic antifungals is best for treating onychomycosis, it is important to remember that dermatophytes are often resistant to common antifungals such as imidazoles and allylamines.
In addition, when diagnosing dermatophyte onychomycosis, there is often a presumption that the parasitization by mycetes may have occurred due to previous structural damage of the lamina caused by another pathology. After lengthy drug treatment to eliminate the dermatophytes, the lamina is still not restored to its original condition.

Conditions that create the confusion with onychomycosis

Nail psoriasis

Unlike onychomycosis, nail psoriasis is very common and can affect the nail laminae of both the hands and feet. “Nail hopping” is an important clinical sign that can facilitate the diagnosis of psoriatic onychopathy and involves the presence of an intact nail in between two or more damaged nail plates. Such a phenomenon is unlikely to appear in onychomycosis, as the mycete would have no reason to skip a nail instead of parasitizing it.
If signs of psoriasis are then present at other body sites, the diagnosis of psoriatic onychopathy becomes automatic.

Onychodystrophy

Onychodystrophy is the second most common cause of confusion when diagnosing onychomycosis. It refers to a nail that can no longer grow healthily due to vascular problems (e.g. senescence, diabetes, vasculopathy, dietary deficiencies, chemotherapy, trauma, etc.). The laminae appear dull, ridged and can sometimes detach from the nail bed. In addition to these defects, the nail is also vulnerable to molds or yeasts that will take advantage of the weaker lamina to enter the nail.
This is not true onychomycosis but rather a fungal contamination due to nail dystrophy.
In such cases where dystrophy and not mycosis is present, treatment for a parasitic fungus is of minimal value. Even if the mold or yeast present were eradicated, the nail remains pathological and unchanged due to the underlying dystrophy.

Treatment considerations

Treating onychomycosis is always difficult, and before embarking on any treatment, it is good to think about the cost/benefit ratio. Key points to consider are: slow growth of the nail plate, toxicity of systemic antifungal drugs, poor efficacy of topical antifungals and frequency of recurrence after treatment.

Confusing treatment options

Recently, laser or photodynamic therapy have become popular to treat onychomycosis, however these treatments have no scientific basis in the cure of the condition and should, therefore, be dismissed.

Dermaclub recommends

The most sensible dermo-podiatric treatment option is to frequently file the parasitized laminae and apply 2S Cream with sulfosalicylic acid daily. The correction of structural foot defects or other behavior that could be aggravating the condition should also be considered.