What are the mechanisms of hyponatremia in alcohol use disorder?

 Based on my literature search, several mechanisms are at play.

Probably the most common is volume depletion, which prevails in many patients admitted to the hospital with acute alcoholism. It is due to low intake and GI losses. Hypovolemia is a non-osmotic signal for vasopressin (ADH) release. Accordingly, vasopressin is secreted regardless of sodium level. 

Another important cause is stress related vasopressin release, an acute form of the syndrome of inappropriate antidiuresis (SIAD). 

Less common but nonetheless important is beer potomania. It is possible to sustain one's caloric intake solely on beer for extended periods of time. All of the solute in beer (ethanol)  is metabolized. So, in effect, drinking beer is drinking free water.   Because patients who subsist on beer for their major source of calories are taking in little or no solute they are unable to excrete sufficient urine volume to maintain free water balance. In pure beer potomania the collecting duct and the vasopressin axis are functioning properly. Therefore, due to the presence of hyponatremia, the urine is maximally dilute. Urine osmolalities of 80 to 100 are seen.

Finally, since alcoholism rarely results in extreme hypertriglyceridemia, pseudohyponatremia is possible. This is not seen unless triglyceride levels are1500 or greater. 

This topic was reviewed in the November 2000 issue of Alcohol and Acoholism. 

Mechanisms of Hyponatremia in Alcohol Patients

This table from the article lists the causes and number of patients in their small study population.

This was a small number of patients and may not be representative sample. Stress related inappropriate antidiuresis was not mentioned in this article but is probably an important mechanism. Two conditions found among the patients in the series, one of each, were cerebral salt wasting and the reset osmostat syndrome. These may have been incidental and not directly related to alcoholism.

In addition, an important article in The New England Journal of Medicine reviewed alcohol related electrolyte disturbances in general. 

Electrolyte Disturbances in Patients with Chronic Alcohol-Use Disorder

In some patients, multiple mechanisms of hyponatremia may overlap.