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1. The most common cause of hyponatremia is hypo-osmolar (hypotonic) hyponatremia.

2. The low osmolality causes water movement into cells, leading to intracellular swell­ing, resulting in neuromuscular excitability, seizures, and coma - when the Na + falls acutely (< 120).

3. Always think of the serum sodium concentration as the ratio of total body sodium to water, with increased total body water content as the key disorder.

4. In the patient with hypotonic hyponatremia, first, clinically assess the volume status.


1. Wilkinson, I. (2017). Oxford handbook of clinical medicine. Oxford: Oxford University Press.
2. Hannaman, R. A., Bullock, L., Hatchell, C. A., & Yoffe, M. (2016). Internal medicine review core curriculum, 2017-2018. CO Springs, CO: MedStudy.
3. Image: no reference available.

Ⓒ A. Manickam 2018

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