Dear Editor, Allogeneic hematopoietic stem cell transplantation (HSCT) has been reported to induce remission of coincidental or sole autoimmune disease [1][2][3]. We report on a patient with myelodysplastic syndrome (MDS) whose remitting seronegative symmetrical synovitis with pitting edema (RS3PE) achieved remission without any treatment after unrelated cord blood transplantation (CBT).A 60-year-old man with a two-month history of morning stiffness in the hand joints, polyarthralgia, and edema of the dorsum of both the hands and feet was admitted to our hospital. Laboratory findings revealed an elevated matrix metalloproteinaise-3 (MMP-3) of 824.1 ng/mL (<121), along with macrocytic anemia. Rheumatoid factor, antinuclear antibody, and anti-cyclic citrullinated peptide antibody were negative. Magnetic resonance imaging (MRI) of the hands demonstrated soft tissue swelling without bone erosion. Based on these data, he was diagnosed with RS3PE. Bone marrow examination revealed dysplasia of the erythroid series and chromosomal abnormality including dup(1)(q21;q42), indicating that macrocytic anemia was due to MDS refractory anemia according to the WHO classification, and with the IPSS intermediate-1 risk group. He was treated with prednisolone, salazosulfapyridine, and etanercept and showed mild improvement of RS3PE symptoms. Eighteen months after diagnosis of MDS, pancytopenia progressed, and the proportion of myeloblasts in the bone marrow increased, which was consistent with the disease progression to refractory anemia with excess blasts-2 (RAEB-2). He received seven courses of azacitidine for MDS RAEB-2 and achieved marrow complete remission with hematological improvement according to the International Working Group (IWG) response criteria [4]. Symptoms of RS3PE improved in parallel with treatment response to MDS. However, since the response to azacitidine was transient, he received an HLA-mismatched CBT for MDS. One month before CBT, MRI showed the presence of fluid in the tenosynovial sheaths of the metacarpal phalangeal (MCP) joint and flexor and extensor tendons of both the hands (Fig. 1a). The number of cord blood nucleated cells was 2.43×10 7 /kg, and the number of CD34-positive cells was 0.97×10 5 /kg. The conditioning regimen consisted of 4 Gy of total body irradiation, intravenous busulfan 9.6 mg/kg, fludarabine 180 mg/m 2 , and cytarabine 12 g/m 2 . Prophylaxis for graft-versus-host disease (GVHD) consisted of intravenous cyclosporine and oral mycophenolate mofetil. His hand dorsum edema and arthralgia disappeared rapidly following the conditioning regimen. Limited chronic GVHD involving the skin occurred, but resolved spontaneously. Immunosuppressive treatment was discontinued 10 months after CBT. Bone marrow examination 12 months after CBT revealed complete remission and complete donor chimerism. Fifteen months after CBT, an MRI of his hands revealed no findings of RS3PE (Fig. 1b), and the serum MMP-3 level had decreased to 48.5 ng/mL.