A 55-year-old male with a history of significant alcohol intake presents with a 2-week history of lethargy. He takes no regular medications and has no other medical disorders. Clinically, he appears malnourished and euvolaemic. Investigations reveal the following:
|
Parameter |
Patient Value |
Adult Normal Range |
|
Blood Results: |
||
|
Na+ |
115 mmol/L* |
134 – 143 |
|
K+ |
3.7 mmol/L |
3.5 – 5.0 |
|
Cl- |
80 mmol/L* |
97 – 107 |
|
HCO3- |
22 mmol/L* |
24 – 34 |
|
Urea |
3.0 mmol/L* |
3.1 – 8.1 |
|
Creatinine |
46 µmol/L* |
50 – 90 |
|
Glucose |
4.1 mmol/L* |
4.4 – 6.8 |
|
Osmolality |
241 mmol/kg* |
271 – 289 |
|
Urine Results: |
||
|
Na+ |
10 mmol/L |
10 – 20 |
|
Osmolality |
53 mmol/kg |
40 – 1200 |
a) What is the most likely cause of the hyponatraemia? (15% marks)
a) Water intoxication/Beer potomania
Key features here are "degenerate alcoholic" "malnutrition" and "euvolaemia". The undoubtedly vast intake of alcohol consists of essentially just water, as the alcohol is readily metabolised into CO2 and H2O. The resulting water excess produces a hypoosmolar hyponatremia which remains euvolemic for as long as the drinking continues. The low urine sodium and minimal urinary osmolality (the lowest value possible is around 40 mmol/kg) suggests that the kidneys are responsibly retaining sodium and doing their best to dump water.
Apart from beer potomania and psychogenic polydipsia, this sort of thing can develop in case of a reset osmostat (eg. in old age), during pregnancy, and in people who embark upon weird crash diets.
Hariprasad MK, Eisinger RP, Nadler IM, Padmanabhan CS, Nidus BD. Hyponatremia in psychogenic polydipsia. Arch Intern Med. 1980 Dec;140(12):1639-42.
Hilden T, Svendsen TL. Electrolyte disturbances in beer drinkers. A specific "hypo-osmolality syndrome". Lancet. 1975 Aug 9;2(7928):245-6.
Thaler SM, Teitelbaum I, Berl T. "Beer potomania" in non-beer drinkers: effect of low dietary solute intake. Am J Kidney Dis. 1998 Jun;31(6):1028-31.
Fox BD.Crash diet potomania. Lancet. 2002 Mar 16;359(9310):942.
Lipschutz JH, Arieff AI. Reset osmostat in a healthy patient. Ann Intern Med. 1994 Apr 1;120(7):574-6