Background Many patients with rheumatoid arthritis (RA) complain of pain in the small muscles of the hand and most develop atrophy of these muscles, but little is known about potential causes.

Objectives Investigate relationships between computer aided 3T DCE-MRI perfusion parameters in the small muscles of the hand and computer aided perfusion measures of inflammation in wrist and MCP joints derived from DCE-MRI data using Dynamika® in patients with RA and normal controls.

Methods 35 RA patients and 5 healthy volunteers had a 3T MRI of the dominant hand. Imaging protocol: coronal STIR, T1 pre- and post- contrast as well as sequential coronal T1-DCE-MRI (18 slices in 9sec, with 30 repetitions) covering the hand, started at the time of iv contrast injection (0.1mmol/kg). DCE-MRI data were corrected for movement and parametric mapping algorithms were applied using Dynamika. In RA the slice with most enhancement was selected, and regions of interests (ROIs) were drawn around the wrist and MCP joint in images from RA patients. In all participants, additional ROI’s were drawn around the anatomical boundaries of the most enhancing small muscle complex between the metacarpal bones. The computed output data in the wrist, MCP and muscle ROIs comprised the mean of: initial rate of enhancement (IRE), maximum enhancement (ME), number of enhancing voxels with plateau and washout enhancement (Np and Nw) and their combinations Np+Nw, ME*Np+Nw and IRE*Np+Nw. RAMRIS scores of synovitis and bone marrow oedema (BME) in the wrist and MCP joints were also performed. RAMRIS for synovitis and bone marrow oedema (BME) was performed. Relationships between DCE-MRI and RAMRIS were assessed by Spearman’s test and controls and RA patients were assessed with T-test. Level of significance: 0.05.

Results Distribution of RAMRIS scores median (Range) in the wrist were: Synovitis 5 (2-9), BME 6 (0-42), and in MCP joints: Synovitis 3 (0-9), BME 0 (0-17). There was a highly significant difference between the number of enhancing voxels Np+Nw, the composite scores of ME*Np+Nw and IRE* Np+Nw (p<0.001) in the small muscles of the hand between RA patients and controls, but no difference between the mean ME and the mean IRE. Table 1 shows the correlations between muscle perfusion and the inflammatory scores of the MCP joints.

No correlation was found between any inflammatory scores in the wrist and muscle perfusion.

Conclusions Healthy controls have low baseline perfusion in the small muscles of the hand with significantly fewer enhancing voxels and lower scores of ME*Np+Nw and IRE* Np+Nw compared to RA patients. In RA, the perfusion of small muscles of the hand correlates to inflammatory activity in the MCP but not the wrist joint. This observation may be directly linked to the inflammatory load seen in RA with MCP joint involvement.

Disclosure of Interest M. Boesen Consultant for: IIndependant non paid consultant to Image Analysis, A. Rastogi: None Declared, O. Kubassova Shareholder of: Image Analysis, P. Taylor: None Declared, R. Bouert: None Declared, M. Cimmino: None Declared, B. Danneskiold-Samsoe: None Declared, S. Amris: None Declared, H. Bliddal: None Declared