A 46-year-old man with Klinefelter syndrome (KS) presented with obliterative phlebitis of the lower legs with a deteriorated renal function, and elevated serum alkaline phosphatase and ataxia levels. Examinations demonstrated tubulointerstitial nephritis, obliterative phlebitis and lymphadenopathy with IgG4+ plasma cell infiltrate and sclerosing cholangitis. Although the serological profile and central nerve system involvement were compatible for systemic lupus erythematosus (SLE), a definite diagnosis of SLE was difficult to make. IgG4-related disease (IgG4-RD) with KS was finally diagnosed, and high dose prednisolone with intravenous cyclophosphamide was initiated and thereafter the patient demonstrated a prompt improvement. This is the first known case demonstrating overlapping IgG4-RD with lupus-like serological and neurological features in a patient with KS, thus highlighting the pathogenic role with the genomic background for IgG4-RD and SLE.
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