The syndrome of inappropriate anti-diuretic hormone secretion concurrent with an acute exacerbation of cystic fibrosis.

Acute exacerbations of cystic fibrosis (CF) can be associated with dehydration, hyponatraemia and hypochloraemia. The syndrome of inappropriate anti-diuretic hormone secretion (SIADH) has also been described in CF patients in the setting of hyponatraemia, but may be under-recognised. Diagnosing SIADH has therapeutic implications as it necessitates fluid and water restriction rather than fluid resuscitation. We report the case of an acute pulmonary exacerbation of CF in which features of SIADH are demonstrated.