Unequal relevance between different subtypes of fingernail psoriasis and psoriatic arthritis.

Nail disease in psoriasis has been found to be associated with psoriatic arthritis (PsA); however, which subtype of nail disease holds greater relevance to PsA remains unclear. This study was performed to explore the associations between three subtypes of fingernail disease (pitting, onycholysis, and hyperkeratosis) and PsA among patients with psoriasis. Patients with psoriasis attending five dermatology clinics in Shanghai between January 2020 and May 2021 were examined for skin, joint, and fingernail changes. Multivariate logistic regression analyses were utilized to test the strength of associations between subtypes of fingernail disease and PsA. The receiver operator characteristic (ROC) curve with area under curve (AUC) was used to evaluate their accuracies in diagnosing PsA. Sensitivity and specificity were also calculated. Of 1985 patients with psoriasis included, 228 (11.5%) patients were diagnosed with PsA, and the remaining patients were cutaneous-only psoriasis (PsC). One-hundred and fifty-seven (68.9%) patients with PsA and 748 (42.6%) patients with PsC had fingernail disease. Adjusted models showed that onycholysis and hyperkeratosis were the only type of fingernail disease independently associated with PsA. This association was further confirmed by the forward conditional stepwise regression model (OR, 95% CI for onycholysis: 2.34, 1.79 to 4.27, p < 0.01; for hyperkeratosis: 1.62, 1.12 to 2.66, p = 0.037). ROC analysis showed that, compared to pitting and hyperkeratosis, onycholysis had higher AUC (0.630) and sensitivity (52.6%). The psoriatic fingernail onycholysis and hyperkeratosis hold greater relevance to PsA than pitting. Clinically, psoriatic patients with fingernail onycholysis and hyperkeratosis should be assessed for arthritis. Key Points • Psoriatic fingernail onycholysis and hyperkeratosis, rather than pitting, are significantly associated with PsA • Clinically, psoriatic patients with fingernail onycholysis and hyperkeratosis should be assessed for arthritis.