Olfactory function in patients with rheumatoid arthritis and its association with disease activity: a cross-sectional case-control study

The aim of this study was to evaluate odor identification and odor threshold in patients with rheumatoid arthritis, compare these measures with those of healthy controls, and investigate their associations with disease activity.

This cross-sectional case-control study with prospective participant recruitment included patients with rheumatoid arthritis and age- and sex-matched healthy controls. Odor identification (OI) was assessed using the 12-item Rapid Sniffin' Sticks test, and odor threshold (OT) was assessed using the modified CCCRC n-butanol test. Disease duration, disease activity scores, and inflammatory markers, including C-reactive protein (CRP), were recorded. Associations between olfactory measures and disease-related parameters were analyzed.

The distribution of odor threshold categories differed significantly between groups (p < 0.001), with higher proportions of anosmia and hyposmia in patients with rheumatoid arthritis than in healthy controls. Odor identification scores did not differ significantly between groups. No statistically significant associations were observed between OT categories or OI scores and disease duration, disease activity scores, or CRP levels. OI scores were higher among methotrexate users than non-users, whereas OT category distribution did not differ significantly according to methotrexate use. Neither olfactory measure was significantly associated with corticosteroid use.

Rheumatoid arthritis was associated with an altered distribution of odor threshold categories, whereas odor identification scores did not differ significantly between groups. No statistically significant associations were observed between the olfactory measures and disease activity, disease duration, or CRP levels. These findings do not establish causality or independence from potential confounders.

III. Key Points • Patients with rheumatoid arthritis had higher proportions of anosmia and hyposmia than healthy controls. • Odor identification scores did not differ significantly between patients with rheumatoid arthritis and healthy controls. • No statistically significant associations were observed between odor threshold categories or odor identification scores and disease activity, disease duration, or CRP levels. • Rheumatoid arthritis was associated with an altered distribution of odor threshold categories; the independence and causal nature of this association remain to be established.