A case of the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) associated with lupus erythematosus in the central nervous system.

We report on a case of the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) associated with lupus erythematosus in the central nervous system (CNS). A 73-year-old woman with essential hypertension suddenly demonstrated consciousness disturbance. Upon her admission, laboratory data showed significant hyponatremia (114 mEq/L) and a lack of body fluid loss. Diminished free water excretion (urine osmolality 684 mOsm/kg) and normal urine Na excretion (FENa 1.70 %) were consistent with the diagnosis of SIADH, which was confirmed by an inappropriately high concentration of plasma antidiuretic hormone (ADH) (15.3 pg/mL at 256 mOsm/kg of plasma osmolality). The hyponatremia was corrected by a combination of oral water intake restriction and saline infusion with furosemide administration until the 20th hospital day. Simultaneously, the presence of exudative pleural effusion in both chest cavities, suggesting the existence of pleuritis, and high titer of anti-nuclear antibody (ANA, 5120×) and anti-double-strand DNA antibody (6500 IU/mL), indicated the subclinical development of systemic lupus erythematosus (SLE), although the diagnostic criteria were not satisfied at that time. On the 34th hospital day, the sudden onset of unknown consciousness disturbance confirmed the diagnosis of SLE as CNS lupus. In previous case reports on SLE and/or SIADH, a few cases in which SLE and SIADH developed concomitantly regularly showed high immunological activities, as in our case. Some common pathophysiological bases might be involved in the concomitant appearance of those disorders.