Fungal infection or nail psoriasis?

Also known as nail psoriasis, this form of psoriasis is localised to the nails. It primarily affects the fingernails. It is estimated that 35 to 50% of patients suffering from psoriasis have lesions localised to the nails. This disease can occur at any age and manifests in various ways. It is caused by the failure of the immune system due to the accelerated renewal of keratinocytes. When psoriasis affects the nail matrix, it causes the appearance of pitted holes on the surface of the affected area. It can also manifest on the nail bed. In this case, the symptoms are:

• The thickening of the nails or the skin under the nails, a condition known as hyperkeratosis;

• The loss of nail transparency with the emergence of pinkish spots;

• Of a nail detachment, onycholysis, and deformation of the nail.

Even though psoriasis is not contagious, it needs to be treated, as its symptoms can impair the patient's quality of life. The appropriate treatments for nail psoriasis depend on its severity. To alleviate the symptoms of this disease, one can opt for:

• Local remedies to be applied directly to the affected area;

• General treatments to be taken orally or by injection;

• The use of biotherapies.

Nail fungus, also known as onychomycosis, is an infection caused by fungi. These most commonly attack the toenails, but they can also develop on the fingernails.

The fungi that cause mycosis are composed of several microorganisms capable of multiplying rapidly. Dermatophytes are responsible for the majority of onychomycosis cases. Particularly the Trichophyton rubrum is the dermatophyte most commonly associated with onychomycosis. It can also cause other fungal skin infections. The fungi responsible for nail mycosis begin their parasitism by first invading the spaces between the toes, known as interdigital spaces, then progress towards the sole of the foot and finally reach the nail itself.

There are also conditions that promote their proliferation such as humidity, the presence of lesions, or perspiration. Nail fungus must be addressed at the first signs of infection to prevent it from worsening over time. Moreover, this condition is contagious. The management of onychomycosis involves applying an antifungal product daily to the area where it develops.

Nail psoriasis is relatively straightforward to diagnose as it is often associated with skin plaques. However, in the absence of these, it can be mistaken for nail fungus, given the numerous similarities between these conditions. Indeed, both diseases alter the appearance of the nail. Nevertheless, the fungus can be distinguished from psoriasis by the fact that it makes the nail brittle and yellow. Psoriasis, on the other hand, causes the appearance of small pits on the nail surface or pinkish spots. Often, the doctor will conduct a mycological sample to confirm the diagnosis. Moreover, it is possible to be affected by both nail fungus and nail psoriasis. Indeed, sensitised nails are more susceptible to fungal attacks.

DUHARD-BROHAN E. Psoriasis unguéal. Annales de Dermatologie et de Vénéréologie (1999).

COGREL O. Psoriasis de l'ongle (Psoriasis unguéal). Association France Psoriasis (2022).