POS0565 IS ACTIVE SYNOVITIS OF METACARPOPHALANGEAL JOINTS A NEUROPATHIC CONDITION IN RHEUMATOID ARTHRITIS PATIENTS? RESULTS FROM A ULTRASOUND STUDY AT LEVEL OF THE PALMAR DIGITAL NERVES

Abstract

Background:Rheumatoid arthritis (RA) is a chronic inflammatory arthritis that primarily affects the joints of hands, wrists, and feet. Anatomical damage (at bone, cartilage and tendon level) occurs as a consequence of a persistent synovial inflammation (1). In RA, periarticular soft tissues, including nerves, may also be involved. In particular, there is a high prevalence of neuropathic conditions such as carpal tunnel syndrome (CTS) in RA patients. In fact, the presence of inflammatory changes can frequently be documented by ultrasound (US) at the level of median nerve (2). Currently available very-high frequency US transducers allow high spatial resolution of small anatomical structures, including the palmar digital nerves.Objectives:The objectives of this study were: to document the presence of dimensional alterations of the palmar digital nerves, particularly in terms of increased cross-sectional area (CSA), and to determine the variables associated with increased CSA, in RA patients.Methods:From September 2020 to December 2020, adult RA patients from a tertiary outpatient clinic were consecutively included regardless of disease activity status. Patients underwent a clinical assessment to determine disease activity using the Clinical Disease Activity Index (CDAI), functional capacity using the QuickDASH, and the presence of neuropathic pain features using the PainDetect Questionnaire (PDQ). In the same visit, patients underwent a US examination of the 2nd to 5th metacarpophalangeal joints (MCPj) of the clinically more involved hand by an operator blinded to the clinical assessment. The presence/absence and US grading of synovitis was recorded for each joint. A third operator, blinded to the clinical and joint US assessment, measured the CSA of each pair of palmar digital nerves from 2nd to 5th finger scanned for assessment joint involvement. The CSA of the palmar digital nerves was measured at the MCPj. The US examinations were conducted with a MyLab Class C (Esaote, Genoa, Italy), with a 6-18 MHz probe for the articular examination, and with an 10-22 MHz probe for the examination of the palmar digital nerves. The serological status, respectively rheumatoid factor (RF) and anti-citrullinated peptide antibodies (ACPA), and the presence of radiographic erosive disease were also recorded for each patient. Statistical analysis was conducted by considering the sum of the CSA for each nerve pair of each finger. CSA was compared with respect to body mass index (BMI), disease duration, disease activity, US synovitis grading, functional capacity, neuropathic pain features, serological characteristics, and erosive status.Results:Sixty-three patients with RA were included, 48 women, 15 men, with a mean age of 62.2 (11.8, standard deviation [SD]) years, a mean disease duration of 10.9 (8.2) years, for a total of 252 MCPj and 504 palmar digital nerves. The CSA of the palmar digital nerves taken individually was 2.3 (0.9) mm2, ranging from 1 mm2 to 8 mm2, and 4.2 (1.5) mm2 as a pair for finger. There was a statistically significant association with disease activity as assessed by the CDAI (p <0.001), and with the grading of US synovitis (p <0.001), while there were no significant associations with any of the other variables.Conclusion:The presence of active RA, both in terms of clinical and ultrasonographic indices, correlates with an increased CSA of the palmar digital nerves. This alteration is probably due to inflammatory mechanisms of the perineural tissues at the level of the MCPj. Active synovitis during RA can somehow be framed as a condition capable of causing neuropathic damage to the palmar digital nerves.