Background Autoimmune processes, contribute to the burden of kidney disease. The reported kidney disease prevalence in patients with rheumatoid arthritis (RA) ranges from 5%>50% based on studies of different designs. Historically, patients with RA-associated renal amyloidosis had higher mortality rates relative to the general population. The occurrence of haematuria, proteinuria, or CKD has been reported to be associated with a 3- to 4-fold increased risk of death. Subclinical decreased kidney function has been identified as an independent risk factor for cardiovascular (CV) events with increase mortality in patients with RA. On the other hand, both rheumatoid arthritis and renal impairment have been reported to be associated with increase prevalence of carpal tunnel syndrome.

Objectives To establish the median nerve thickness (measured by ultrasound) in RA and its relation to renal function.

Methods 120 RA patients were recruited through a specialized rheumatology clinic. The US measurements were performed by the same person. Patients were sitting with their forearm resting in a supinated position on a small table. The US probe (an 8–16 MHz linear array transducer) was held as lightly as possible to avoid disturbing the anatomy of the nerve. The median nerve was examined at the entrance of the carpal tunnel, between the pisiform bone and the tubercle of the scaphoid bone, where the distal volar crease is an external pisiform landmark. A continuous trace was made just within the hyperechogenic boundary of the nerve. The cross-sectional area of the median nerve was calculated directly by the software of the US equipment. Each median nerve was measured three times, and the mean value was used for further analyses. Modification of Diet in Renal Disease (MDRD) equation used to estimate the Glomerualr Filatration Rate (GFR). The average of the right and the left areas of the median nerve were used when exploring bivariate correlations to the renal variables (Pearson's correlation coefficients). All statistics were performed using STATA programe.

Results the average median nerve thickness was 9.79±2.6 mm² (Range 1.5 -22.25). The average GFR was 122±20 ml/min (59.6–286). Thickness of the median nerve was positively associated with the age of the participants (p=0.03, CI: 0.00, 0.08), body mass index (p=0.04, CI: 0.00, 0.21), uric acid level (p=0.033, CI: 0.00, 0.01), and urine microalbumin (p=0.04, CI 0.00, 0.01). GFR showed no significant relation the thickness of the median nerve.

Conclusions RA patients without symptoms or clinical signs have a median nerve thickness that is positively correlated to the level of microalbumin and uric acid. Whether sosnographic examination of the median nerve would be helpful in predicting who is going to have a deteriorated renal function need to be explored in a larger study.

References

1. Boers, M., et al., Subclinical renal dysfunction in rheumatoid arthritis. Arthritis Rheum, 1990 33(1): p. 95–101.

2. Daoussis, D., et al., Cardiovascular risk factors and not disease activity, severity or therapy associate with renal dysfunction in patients with rheumatoid arthritis. Ann Rheum Dis, 2010. 69(3): p. 517–21.

3. Pathan, E. and V.R. Joshi, Rheumatoid arthritis and the kidney. J Assoc Physicians India, 2004 52: p. 488–94.

References

Disclosure of Interest None declared