Nail Psoriasis: How to recognise it for better treatment?

Psoriasis is a chronic inflammatory skin disease that evolves in flare-ups affecting at least 2% of the French population. It manifests itself through the appearance of red patches covered with scales, which are like flakes of varying thickness. This dermatosis is due to a dysregulation of the immune system, causing an overproduction of keratinocytes by the skin. Thus, an accumulation of immature keratinocytes is observed on the skin surface: this is referred to as hyperkeratosis. The patches can cause a scratching sensation in about one in two cases.

Psoriasis hasseveral causes. Indeed, individuals suffering from psoriasis often have genetic predispositions, but there are also acquired factors (stress, diet, infection...). Psoriasis is therefore a skin disease that predominantly affects the scalp, flexion zones (elbows, knees), the navel, the lower back, the buttocks, etc. It can also manifest in the nails. There is a joint disease, known as psoriatic arthritis, which is much rarer but can be associated with skin involvement.

Nail involvement, or ungual psoriasis, is common in patients with cutaneous psoriasis, as it is observed in nearly half of the cases. However, isolated nail involvement is rarer. As mentioned above, psoriasis is a multifactorial disease involving genetic predispositions. Regarding ungual psoriasis, scientists have identified a variant located in the IL1RN gene which codes for a pro-inflammatory cytokine, IL-1A. This variant is believed to be responsible for the changes in the nail.

For your information : IL1RN is an antagonist receptor to Interleukin-1 (IL-1). In other words, it is a major regulator of the pro-inflammatory activity of IL-1A. It works by inhibiting its binding to the cellular receptor IL-1R1. A study has shown that mutations in the IL1RN gene are the cause of an auto-inflammatory disease in which affected children exhibit nail changes similar to those observed in patients with psoriasis.

Nail psoriasis is more commonly observed in men than in women. Studies have also shown that smoking increases the risk of nail psoriasis. Therefore, individuals suffering from skin psoriasis are more likely to develop nail psoriasis if they smoke.

Nail psoriasis is associated with other pathologies, primarily rheumatism psoriatic. Indeed, individuals with nail psoriasis have a significantly higher risk of developing joint damage.. The psoriatic rheumatism causes inflammation either of the joint itself, or of the tendon insertions (enthesopathy), which results in significant pain.

Another condition associated with nail psoriasis isonychomycosis, which is a fungal (i.e., caused by a fungus) infection of the nail. Indeed, 30% of patients with nail psoriasis concurrently have onychomycosis. This link could be explained by the fact that the deformities observed in nail psoriasis could promote the onset of fungal infection at the nail level. Conversely, the fungal infection of the nail could promote the onset of psoriasis at the nail level according to the Koebner phenomenon, which describes the development of new lesions at sites of trauma. Some doctors advise checking for the presence of onychomycosis before starting immunosuppressive treatment for psoriasis, as the latter could exacerbate the fungal infection.

Nail involvement in psoriasis is therefore common. But then, how do we recognise nail psoriasis?

• A: There are "little holes" that we call punctate deformations or thimble pitting. This is the most common clinical manifestation of nail psoriasis. These are not specific to psoriasis, they can be of mechanical origin, particularly in people who do manual work.

  B: Here we observe a distal onycholysis, characterised by the progressive detachment of the nail. The body of the nail separates from the nail bed, coupled with a pseudo-leukonychia which refers to the presence of white spots on the surface of the nail.

  C : Figure C illustrates a nail dystrophy with the presence of red spots at the level of the nail lunula, that is, above the cuticle.

  D: The last alteration is the trachyonychia. This is also a nail dystrophy. The surface of the nail is rough with longitudinal ridges and cracks.

• A: In this image, we can see linear subungual haemorrhages. These haemorrhages can be identified by thin red or brown lines under your nails.

  B : This figure illustrates a subungual hyperkeratosis, characterised by an accumulation of cells under the nail causing a thickening of the nail.

  C: This nail alteration is an abnormality in the nail colour, referred to as the oil drop or salmon patch. It is characterised by translucent yellow-red spots on the nail bed.

  D: It is possible to observe a complete or near-complete nail detachment (onycholysis) from the nail plate, as illustrated in figure D.

Firstly, it is necessary to consult a doctor to prescribe a suitable treatment, as nail psoriasis should not be overlooked. Alongside this, there are good practices to adopt:

• Avoiding Micro-Traumas:

  Micro-traumas exacerbate nail psoriasis (Koebner phenomenon). Therefore, it is necessary to avoid anything that is a source of aggression for the nails, contact with irritating agents or even the act of biting the nails. It is also recommended to wear protective gloves during manual activities and to keep your nails as short as possible.

• Protection against moisture:

  As previously explained, there is a connection between nail psoriasis and onychomycosis, as 30% of patients with nail psoriasis also have onychomycosis. Fungal colonisation of the nail is a factor that exacerbates psoriasis. Therefore, it is important to protect nails affected by psoriasis from moisture, given that it provides a favourable environment for fungal growth.

• PUIG L. & al. Nail psoriasis. Academia Espanola de Dermatoligica y Venereologia (2022).