RESUMO
Amyotrophic lateral sclerosis (ALS) rarely presents with hyponatraemia caused by syndrome of inappropriate antidiuretic hormone secretion (SIADH). We present a patient with hyponatraemia of multifactorial aetiology, in whom, after withdrawal of the drugs that contributed to this ionic alteration, SIADH secondary to ALS was confirmed. After initiating treatment with urea, sodium levels were normalized. LEARNING POINTS: Amyotrophic lateral sclerosis (ALS) is rarely associated with syndrome of inappropriate antidiuretic hormone secretion (SIADH).In a patient with chronic hyponatraemia due to SIADH, administration of urea, as recommended by clinical practice guidelines, increases sodium levels.We present the case of a patient with SIADH due to ALS where hyponatraemia was resolved using urea.