Background Involvement of hands is a frequent finding in polymyalgia rheumatica (PMR) and can lead to misclassification as late-onset rheumatoid arthritis (RA). Objective To compare the inflammatory pattern as shown by contrast-enhanced MRI (ceMRI) of hand involvement in PMR to seropositive RA (RA+). Methods MRIs of patients diagnosed with PMR and clinically suspected hand involvement and with RA+, matched for age/sex, were analysed retrospectively. Synovitis, osteitis and erosions of metacarpophalangeal (MCP) joints 2–5 plus tenosynovitis of flexor/extensor compartments were evaluated using the Rheumatoid Arthritis MRI Score. For assessment of periarticular inflammation around MCP joints, a semi-quantitative scoring was introduced. Results Distribution of synovitis scores differed significantly between the groups with mostly minor and occasionally moderate synovitis in PMR versus uniformly distributed total scores in RA+. Scores of periarticular inflammation were significantly higher in PMR. Tenosynovitis of extensors and flexors was prevalent in both groups, but flexor tenosynovitis was significantly more prevalent in PMR. Detection of erosions and osteitis was absent in PMR cases but prevalent in RA+ (all p<0.001). A combination of minor to moderate synovitis together with severe periarticular inflammation of an MCP joint represented a characteristic finding in PMR and, if evident in at least one MCP joint, differentiated the groups with a sensitivity and specificity of 78.4% and 78.4%, respectively. Specificity improved to 90.2% at the expense of sensitivity (70.6%) when this characteristic inflammatory pattern was present in more than one MCP joint per hand. Conclusion Hand involvement in PMR could be clearly differentiated in ceMRI from RA+ by the intensity of periarticular inflammation of MCP joints.
Fruth et al. (Wed,) studied this question.