Rare Case of Remitting Seronegative Symmetrical Synovitis with Pitting Edema Syndrome with Monoclonal Gammopathy of Undetermined Significance.

BACKGROUND Remitting seronegative symmetrical synovitis with pitting edema (RS3PE) is a rare condition with underlying polyarthritis, pitting edema, and negative rheumatoid factor. It can be associated with an underlying rheumatological condition or can present as a paraneoplastic syndrome with malignancy. We present a rare case of RS3PE associated with monoclonal gammopathy of undermined significance (MGUS). CASE REPORT A 62-year-old man presented in ambulatory medicine clinic with 3-month swelling of distal lower extremities that progressed to distal upper extremities. He had pain and morning stiffness in hands, left elbow, and left shoulder. Examination revealed 3+ pitting edema in bilateral hands, feet, legs, and thighs. Laboratory studies revealed normal blood counts and renal and liver functions. Erythrocyte sedimentation rate was normal; C-reactive protein was mildly elevated (0.7 mg/dL). Echocardiogram and computed tomography of chest, abdomen, and pelvis revealed mild splenomegaly (14.5 cm). Serum protein electrophoresis revealed IgG kappa monoclonal peak of 0.1 g/dL. Beta-2 microglobulin was elevated (7.4 mg/L); LDH was elevated (264 U/L). No lytic lesions were present in bones. RS3PE was diagnosed based on established diagnostic criteria. Prednisone produced significant improvement in swelling within 72 h of start; however, he required a longer duration of steroid treatment due to relapse and continued periodic MGUS surveillance. CONCLUSIONS Our case highlights the importance of awareness of this condition in general practice to help with timely diagnosis and intervention, as this condition is steroid responsive. Also, it is important to screen for underlying autoimmune condition, hematological, and solid organ malignancies with appropriate workup.