Comparison of clinical and dermoscopical nail findings of rheumatoid arthritis, ankylosing spondylitis, psoriatic arthritis and psoriasis: A prospective study.

Psoriasis (PsO), psoriatic arthritis (PsA), rheumatoid arthritis (RA), and ankylosing spondylitis (AS) are chronic inflammatory disorders classified as immune-mediated inflammatory diseases (IMIDs). Although these diseases share common pathogenic mechanisms, they can affect different parts of the body. Nail involvement is important in PsO. However, nail findings in RA and AS have not been extensively investigated despite their inflammatory presentation, similar to PsO. This study aimed to investigate clinical and onychoscopic nail findings in patients with RA and AS and compare their distribution and patterns with those observed in patients with PsO and PsA. One hundred patients (25 in each group) with confirmed diagnoses of PsO, PsA, AS, and RA and at least 1 clinically detectable nail finding were included. A total of 1000 fingernails were examined clinically, and 200 fingernails were examined onychoscopically. The distributions of clinical and onychoscopic findings were assessed and compared across the 4 disease groups. Demographic data, laboratory findings (C-reactive protein, human leukocyte antigen B27, rheumatoid factor, anti-cyclic citrullinated peptide), PsO Area and Severity Index, and Nail PsO Severity Index were recorded. Pitting and onycholysis were the most common findings in PsO and PsA, leukonychia predominated in AS, and vertical ridges/trachyonychia were frequent in RA. Onychoscopy showed that clustered dotted vessels were significantly more frequent in PsO and PsA, whereas parallel dotted/short linear vessels ("fish school-like pattern") were significantly more frequent in RA. Megacapillaries, microhemorrhagic dots, and coiled and tortuous capillaries were numerically more frequent in AS. Some vascular findings were associated with elevated C-reactive protein, human leukocyte antigen B27 positivity, and rheumatoid factor positivity. Nail findings in patients with IMIDs may reflect underlying inflammatory and vascular changes. Richer nail findings in PsO and PsA may be linked to keratinocyte-driven inflammation, whereas vascular alterations may play a more prominent role in the nail findings observed in RA and AS. Differences in clinical and onychoscopic nail patterns across disease groups suggest that detailed nail examination and onychoscopy may provide supportive clinical clues and aid in the clinical differentiation of IMIDs.