Hypothalamic adipic hypernatraemia syndrome with normal osmoregulation of vasopressin

Adipsic hypernatremia in a young Sudanese child, challenges in a limited-resource setting: a case report

Adipsia is a rare condition characterized by a lack of thirst due to a defect in specific osmoreceptors located in the hypothalamus. The disorder is characterized by failure to maintain the body’s normal plasma osmolality (POSM), resulting in chronic or recurrent severe hypernatremia and dehydration. Adipsia is usually accompanied by central diabetes insipidus (DI). Isolated adipsia (without DI) is very rare, with causes ranging from congenital central nervous system malformations to acquired anterior hypothalamic lesions. The diagnosis and management of the condition are considerably challenging for both clinicians and patients/parents, especially in a resource-limited setting. We here in present the first case report of adipsia from Sudan; a young child with isolated adipsia, diagnosed after recurrent severe hypernatemic dehydration episodes. The report portrays the unique challenges in suspecting, diagnosing, and managing the condition in a limited-resource setting.

Hypodipsic-hypernatremia syndrome in an adult with polycythemia: a case report

Background

Hypernatremia is a very common electrolyte disorder and is frequently encountered in out-patient as well as in-hospital settings. We describe an adult who was found to have unexplained relative polycythemia and episodic hypernatremia. A diagnosis of idiopathic hypodipsic-hypernatremia syndrome was made and the patient was managed with a water-drinking schedule.

Case presentation

A 24-year-old South African-Indian man was found to have polycythemia in association with episodes of hypernatremia. Investigations indicated that he had relative polycythemia. He experienced no thirst at a time when his serum sodium concentration was found to be 151 mmol/L. Further testing indicated that his renal response to arginine vasopressin was intact and magnetic resonance imaging of his brain revealed no hypothalamic lesions. A diagnosis of idiopathic hypodipsic-hypernatremia syndrome was made and he was managed with a water-drinking schedule that corrected his hypernatremia.

Conclusion

Hypodipsia should always be considered when a patient without physical or cognitive disability presents with unexplained episodic hypernatremia or with relative polycythemia.

Collecting duct principal cell transport processes and their regulation

The principal cell of the kidney collecting duct is one of the most highly regulated epithelial cell types in vertebrates. The effects of hormonal, autocrine, and paracrine factors to regulate principal cell transport processes are central to the maintenance of fluid and electrolyte balance in the face of wide variations in food and water intake. In marked contrast with the epithelial cells lining the proximal tubule, the collecting duct is electrically tight, and ion and osmotic gradients can be very high. The central role of principal cells in salt and water transport is reflected by their defining transporters-the epithelial Na(+) channel (ENaC), the renal outer medullary K(+) channel, and the aquaporin 2 (AQP2) water channel. The coordinated regulation of ENaC by aldosterone, and AQP2 by arginine vasopressin (AVP) in principal cells is essential for the control of plasma Na(+) and K(+) concentrations, extracellular fluid volume, and BP. In addition to these essential hormones, additional neuronal, physical, and chemical factors influence Na(+), K(+), and water homeostasis. Notably, a variety of secreted paracrine and autocrine agents such as bradykinin, ATP, endothelin, nitric oxide, and prostaglandin E2 counterbalance and limit the natriferic effects of aldosterone and the water-retaining effects of AVP. Considerable recent progress has improved our understanding of the transporters, receptors, second messengers, and signaling events that mediate principal cell responses to changing environments in health and disease. This review primarily addresses the structure and function of the key transporters and the complex interplay of regulatory factors that modulate principal cell ion and water transport.