Recurrent severe hypernatraemia in a young patient: a disconnect between osmoreceptor function and drinking behaviour

Chronic hypernatraemia is uncommon in younger individuals. Established knowledge indicates that hypernatraemia in this age group often results from impaired thirst perception. Prior research has shown that osmoregulatory mechanisms usually involve the hypothalamus and posterior pituitary. However, the mechanisms behind persistent hypernatraemia despite normal osmoregulation remain unclear. This gap motivated the investigation of a unique case where normal osmoregulatory function coexisted with inappropriate drinking behavior. No prior work had resolved how thirst appreciation could fail independently of osmoreceptor function. The patient's clinical presentation raised questions about the role of intracranial structural anomalies in fluid balance. This case adds to the literature on the neurophysiological basis of fluid regulation.

The aim of this case report is to describe a patient with recurrent severe hypernatraemia despite normal osmoregulatory function. The specific problem involves a disconnect between thirst perception and drinking behavior. The motivation stems from the rarity of such cases and the need to understand the underlying pathophysiology. The patient's plasma sodium levels reached 175 mmol/L, indicating severe dehydration. The presence of a large intracranial cyst suggested a possible anatomical cause for the dysfunction. The study sought to clarify how normal vasopressin and thirst mechanisms could coexist with inappropriate fluid intake. The authors aimed to highlight the clinical and diagnostic challenges in managing such cases. This case contributes to the understanding of osmoregulatory disorders in young patients.

The study utilized clinical evaluation and formal osmoregulatory testing. The patient's plasma sodium levels were measured during hospital admission. Urine osmolality was assessed to evaluate vasopressin reserve. MRI imaging was performed to examine intracranial structures. Thirst and vasopressin responses were tested under controlled conditions. The patient's drinking behavior was observed and compared to expected responses. The presence of a large extra-axial cyst was confirmed through imaging. The posterior pituitary bright spot was preserved, indicating normal vasopressin storage. The study focused on the functional disconnect between osmoreceptor activity and drinking behavior.

The patient presented with plasma sodium of 175 mmol/L, indicating severe hypernatraemia. Urine osmolality was 894 mOsm/kg, suggesting normal vasopressin reserve. MRI revealed a large extra-axial cyst without hypothalamic damage. Osmoregulatory studies showed normal vasopressin secretion. Thirst perception was intact, but drinking behavior was inadequate. The patient's response to osmotic stimuli was not translated into fluid intake. The cyst was localized away from key osmoregulatory structures. The findings suggest a functional rather than anatomical cause for the drinking behavior deficit.

The authors concluded that the patient's hypernatraemia resulted from a functional disconnect between thirst perception and drinking behavior. The presence of an intracranial cyst likely disrupted central fluid regulation pathways. The patient's osmoregulatory function remained intact, as evidenced by normal vasopressin and thirst responses. The management challenge lies in maintaining adequate fluid intake to prevent recurrence. The case highlights the importance of considering structural brain anomalies in hypernatraemia. The authors propose that the cyst may interfere with the central drive to drink despite normal osmoreceptor function. This case expands the understanding of osmoregulatory disorders in young patients. The findings suggest a need for further investigation into the neurophysiological basis of fluid regulation.