A 45-year-old patient presented to the emergency department with a five-day history of nausea and vomiting and one day of slurred speech. Syndrome of inappropriate antidiuretic hormone secretion (SIADH) was suspected due to sodium level of 110 mmol/l.
a) List five alternative differential diagnosis in this patient with severe hyponatremia, and a high urine sodium and osmolality? (25% marks)
b) Outline the management principles for the use of hypertonic saline (3% NaCl) in symptomatic acute hyponatremia and include the calculations in your answer. (50% marks)
c) List five risk factors for development of osmotic demyelination syndrome. (25% marks)
Aim: To explore the candidate knowledge of SIADH and allow the candidate to display familiarity with the clinical use of 3% saline.
Key sources include: Paper 2009.1 Q14.4, 2017.2 Q5, CanMEDS Medical Expert.
Discussion. The successful candidate in part a was able to list differential diagnoses for severe hyponatraemia AND a high urinary sodium and osmolality as requested. Candidates scored less marks if they listed general causes of hyponatraemia.
Calculations were asked for in part b and candidates who provided an estimation of the sodium deficit and calculated the amount of 3% saline required to correct it scored highly. The expert pass commented on rates of administration, provided rationale behind the recommendations, and provided safe guidelines for sodium correction over 24 hours in the context of the acute symptomatology. Many candidates were unable to list five risk factors for part c. This may be due to a knowledge deficit or misreading of the question. Candidates are reminded to read the questions carefully and attempt to answer every question.
The college refer to Question 14.4 from the first paper of 2009, which asked about the calculation of a sodium deficit, and Question 5 from the second paper of 2017, which was all about the use of hypertonic saline.
The lazy man's classification of sodium disturbances was basically designed to answer this sort of differential-generating exercise. The stem of the question gives you nausea vomiting and slurred speech, which might either indicate that the examiners wanted you to suspect hypovolemia, or to explain why the hypertonic saline is indicated (symptomatic hyponatremia), or to suggest that some sort of sinister intracranial horror is quietly lurking. so, the list of differentials would therefore incorporate:
The question on the management principles for the use of hypertonic saline in this case contains a landmine, the word "acute" nestled in among all the other stem verbiage. This SAQ is specifically asking about the management of acute symptomatic hyponatremia, which requires emergency sodium replacement at a rate which is higher than what you would normally be comfortable with, to rapidly elevate the sodium to something like 115-120.
The management principles can be boiled down to this:
Risk factors for osmotic demyelination include:
Lee, Jennifer Ji Young, et al. "Management of hyponatremia." Canadian Medical Association Journal 186.8 (2014): E281-E286.
Lazaridis, Christos, et al. "High-Osmolarity Saline in Neurocritical Care: Systematic Review and Meta-Analysis*." Critical care medicine 41.5 (2013): 1353-1360.
R J Martin Central pontine and extrapontine myelinolysis: the osmotic demyelination syndromes J Neurol Neurosurg Psychiatry 2004;75:iii22-iii28 doi:10.1136/jnnp.2004.045906
Spasovski, Goce, et al. "Clinical practice guideline on diagnosis and treatment of hyponatraemia." European Journal of Endocrinology 170.3 (2014): G1-G47.
Adrogue, H. J., and N. E. Madias. "Aiding fluid prescription for the dysnatremias." Intensive care medicine 23 (1997): 309-316.