Nail involvement, or nail psoriasis, is common in patients with skin psoriasis, as it is observed in nearly half of the cases. However, isolated nail involvement is rarer. As mentioned earlier, psoriasis is a multifactorial disease involving genetic predispositions. Regarding nail 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 tobacco 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 involvement.. The rheumatism psoriatic is responsible for inflammation either of the joint itself, or of the insertion of the tendons (enthesopathy), which causes 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 connection could be explained by the fact that the deformities observed in nail psoriasis could promote the development of fungal infections at the nail level. Conversely, the fungal infection of the nail could promote the development 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 recognize nail psoriasis?