Syndrome of inappropriate antidiuretic hormone secretion as central nervous system lymphoma relapse sign of nodal diffuse large b-cell lymphoma

A woman (65) with nodal diffuse large B-cell lymphoma in remission developed confusion and communication loss before the 6th chemotherapy. She had no fever and no meningeal sign.Biochemistry revealed hyponatremia consistent with the secretion of inappropriate ADH.MRI showed contrast enhancement on the mesencephalic aqueductus cerebri and on 3rd ventricle.Cerebrospinal fluid had low glucose, high protein, and lymphocytes. Central nervous system lymphoma with SIADH as a relapse sign was diagnosed.