[Neuroleptic malignant syndrome associated with the inadequate antidiuretic hormone secretion syndrome]

Neuroleptic malignant syndrome (NMS) is an adverse reaction of an idiosyncratic nature to drugs having antidopaminergic activity. Pathogenesis is largely disputed. An NMS case is presented which was triggered by flupentixol and was associated with severe hyponatremia (116 mmol/l upon admission). Both clinically and analytically, the hyponatraemia fulfills criteria to be considered secondary to an inappropriate secretion of antidiuretic hormone (SIADH). Other possible causes of hyponatraemia were ruled out. After early treatment with dopaminergic agonists and water restriction, both conditions improved in parallel. The different pathogenetic possibilities which may explain the temporal coexistence of both syndromes in the same patient are discussed. The association of these two conditions is in favour of a probable central pathogenetic cause for NMS. On the other hand, it is suggested that hyponatraemia may mask the diagnosis of NMS.