Hyponatremia in a patient with chronic inflammatory disease

A 66-year-old man was admitted with destructive arthropathy, and calcium pyrophosphate dihydrate was demonstrated in the synovial fluid specimen. He was found to have a hyponatremia. The serum sodium concentration was 121 mmol/l, plasma arginine vasopressin (AVP) 6.6 pmol/l, and serum interleukin (IL)-6 96 pg/l. The clinical findings suggest the diagnosis of syndrome of inappropriate secretion of antidiuretic hormone (SIADH). However, destructive arthropathy with increased values of C-reactive protein and IL-6 is the only background of SIADH in this patient. We suggest the possibility that IL-6 produced at inflammatory lesions may have stimulated an excessive release of AVP resulting in the hyponatremia and hypochloremia of SIADH.