How to treat nail psoriasis?

Nail psoriasis affects the nails of the hands and/or feet. Its primary cause is the overly rapid renewal of the immune system. The manifestation of this disease depends on the location of the affected area and can often be mistaken for a nail fungus. When nail psoriasis affects the nail matrix, it is recognised by the grooves and small holes that form on the surface of the nail. When nail psoriasis develops at the level of the nail bed, it causes:

• A change in nail colour that presents with pinkish spots;

• A detachment or onycholysis;

• Subungual thickening or hyperkeratosis.

The progression of psoriasis varies from one individual to another. It is estimated that it affects 61% of patients with cutaneous psoriasis. Most often, this disease alternates unpredictable flare-ups with periods of remission.

The treatment of nail psoriasis is determined based on the specific location of the nail damage, particularly if the nail matrix is affected or not.

In the event of non-matricial subungual psoriasis.

For this type of nail psoriasis, topical treatments are sufficient. Local corticosteroids and care products containing vitamin D can treat psoriasis plaques. Indeed, the corticosteroids have an anti-inflammatory action by inhibiting the NF-kB transcription factor through the activation of the IkB gene transcription. They also help to modulate the immune response by inhibiting the function of immune cells, particularly T lymphocytes and macrophages. This reduces the release of pro-inflammatory substances by these cells and thus attenuates the heightened immune response observed in individuals affected by psoriasis.

Vitamin D analogues, such as calcipotriol or calcitriol, are anti-proliferative, meaning they combat the excessive multiplication of certain skin cells, particularly on keratinocytes, by inhibiting the progression from the G1 phase to the S phase. If there is no improvement, it is possible to use a 1% fluoro-5-uracil solution to be applied morning and evening for 6 months, brushing around the nail contour. This solution is reserved for when the nail is not detaching, as one of the side effects of fluoro-5-uracil is to promote onycholysis.

In the event of damage to the nail matrix.

In such cases, topical treatments do not prove to be very effective. It is rather recommended to consider intralesional corticosteroid injections. These are carried out once a month over a period of six months. In some studies, it is mentioned that triamcinolone acetonide, a corticosteroid, is used diluted in saline to achieve a concentration of 5 mg/mL and that 0.1 to 0.2 mL will be injected. When injectable corticosteroids are not effective, some authors have reported that the injection of 2.5 mg of methotrexate on each side of the nail, at the level of the proximal nail fold, can be beneficial at a rate of one injection per month for six months.

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

• SAMUEL S. & al. Vitamin D's role in cell proliferation and differentiation. Nutrition Reviews (2008).

• BARAN R. Comment reconnaître et traiter un psoriasis unguéal. La Presse Médicale (2014).

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