Clinical, radiological, and biochemical characteristics in patients with diseases mimicking polymyalgia rheumatica

To find out clues to differentiate between polymyalgia rheumatica (PMR) and other diseases that mimic PMR. We studied Japanese patients with PMR (n = 7), pseudogout (n = 1), remitting seronegative symmetrical synovitis with pitting edema (RS3PE) syndrome (n = 1), and post-infectious polyarthritis (n = 1). The distribution of inflammation in patients was evaluated using a gallium-67 scintigraphy. We measured serum C-reactive protein (CRP), matrix metalloproteinase-3 (MMP-3), and vascular endothelial growth factor (VEGF) in patients before and after treatment. Further, we compared the clinical course of PMR with that of other diseases that mimic PMR. Patients with pseudogout, RS3PE syndrome, post-infectious polyarthritis manifested similar changes in scintigraphic findings and serum CRP, MMP-3, and VEGF levels to PMR before the treatment. A significant reduction in serum CRP levels at one week after use of nonsteroidal anti-inflammatory drugs (NSAIDs) is a good clue to differentiate pseudogout and post-infectious polyarthritis from PMR. Chondrocalcinosis in the radiographs of joints is also effective to differentiate pseudogout from PMR. A small reduction of CRP levels after NSAIDs use and promptly ameliorated CRP and symptoms by a low-dose steroid therapy, which was commonly observed in patients with PMR, were also found in a patient with RS3PE syndrome. Pitting edema of the back of hands and gallium uptake in metacarpophalangeal (MCP) joints were useful to differentiate RS3PE syndrome from PMR. In conclusion, pseudogout, RS3PE syndrome, post-infectious polyarthritis should be included in the spectrum of diseases mimicking PMR. A promptly decreased serum CRP level by NSAIDs is a good clue to differentiate pseudogout and post-infectious polyarthritis from PMR. Pitting edema of the back of hands and symmetric gallium uptake in MCP joints are characteristic for RS3PE syndrome.