AVP and Hyponatremia: In patients with systemic lupus erythematosus who present with severe hypotonic hyponatremia, the syndrome of inappropriate antidiuretic hormone secretion should be strongly considered only after careful exclusion of endocrine causes (adrenal insufficiency and hypothyroidism) and drug-induced hyponatremia (e.g., thiazide diuretics, selective serotonin reuptake inhibitors, and antiepileptic agents, including carbamazepine and cyclophosphamide).