Rheumatoid arthritis associated with high levels of immunoglobulin A: Clinical and biological characteristics

We measured the serum immunoglobulins in 191 patients with rheumatoid arthritis (RA) over an 8 month period, looking for a relationship between high IgA levels, disease activity, and clinical and biological features. Twenty-nine patients with a polyclonal hyperimmunoglobulin A (IgA) (15.2%) above 5 g/l constituted group A. A control group of 29 randomized RA patients with normal IgA levels was studied over the same period (group B). The mean serum IgA concentration was significantly elevated in group A: 6.6 ± 1.8 g/l versus 2.8 ± 0.9 g/l in group B (p < 0.01). In group A, microscopic haematuria occurred in 20.7% of the cases, as against 3.4% from group B (p < 0.05). Furthermore, the incidence of unilateral sacroiliitis and of arthritis of the distal interphalangeal joints was significantly increased in group A (41.4% and 34.5%, respectively) against 6.9% and 3.4% in group B (p < 0.01) and this correlated with a high IgA serum level (p < 0.01). On the other hand, neither disease activity nor the biological parameters of inflammation were influenced by the level of IgA. Patients with RA associated with high levels of IgA are characterized by a significant increase in the incidence of distal interphalangeal arthritis, unilateral sacroiliitis and microscopic haematuria. These clinical and biological features could define a distinct subgroup of patients with RA.