Introduction: Pleural involvement is well recognised in rheumatoid arthritis. Despite the now established role of physician-led thoracic ultrasound in pleural disease, there remains a paucity of research into characterising the sonographic features of rheumatoid pleuritis.

Aim: To examine the sonographic appearance of established rheumatoid effusions.

Methods: A retrospective analysis was performed for all rheumatoid arthritis patients who underwent thoracic ultrasound, with or without intervention, at the John Radcliffe Hospital, Oxford, from July 2015 to January 2023.

Results: Sixteen patients of median age 65 years underwent 31 episodes of thoracic ultrasound and 25 pleural procedures. Half of the patients were male; 11 (81%) were seropositive, 5 (31%) manifested with rheumatoid-related parenchymal changes.

In 16 (52%) instances of thoracic ultrasound, the effusion was moderate in size, measuring 2-3 rib spaces. Median maximal depth of effusion was 7.5 cm. In 28 (90%) instances, the fluid was echogenic. In 18 (58%), there were no septations. Pleural thickening was examined for in 11 (35%) instances and measured in 1 (3%).

Fluid analyses yielded exclusive exudates, with median protein 42 g/L, median glucose 3.35 mmol/L and median LDH 1146 IU/L.

Conclusion: Most rheumatoid effusions referred to a pleural service were moderately sized, non-septated and echogenic, yielding inflammatory exudates. Pleural thickening was not routinely screened for or measured on ultrasound. This highlights the important need for developing a systematic sonographic approach to characterising rheumatoid pleuritis, and in depth assessments of patients in rheumatoid clinics for earlier signs of pleural disease.