The syndrome of inappropriate
antidiuretic hormone secretion (
SIADH) can occur following
traumatic brain injury (TBI), but is usually transient. There are very few case reports describing chronic
SIADH and all resolved within 12 months, except for one case complicated by meningo-
encephalitis. Persistent symptomatic
hyponatremia due to chronic
SIADH was present for 4 years following a TBI in a previously well 32-year-old man.
Hyponatremia consistent with
SIADH initially occurred in the immediate period following a high-speed motorbike accident in 2010. There were associated complications of post-traumatic
amnesia and mild cognitive deficits. Normalization of serum
sodium was achieved initially with fluid restriction. However, this was not sustained and he subsequently required a permanent 1.2 l restriction to maintain near normal
sodium levels. Multiple episodes of acute symptomatic
hyponatremia requiring hospitalization occurred over the following years when he repeatedly stopped the fluid restriction. Given the ongoing nature of his
hyponatremia and difficulties complying with strict fluid restriction,
demeclocycline was commenced in 2014. Normal
sodium levels without fluid restriction have been maintained for 6 months since starting
demeclocycline. This case illustrates an important long-term effect of TBI, the challenges of complying with permanent fluid restrictions and the potential role of
demeclocycline in patients with chronic
hyponatremia due to
SIADH.
LEARNING POINTS: Hyponatraemia due to
SIADH commonly occurs after TBI, but is usually mild and transient.Chronic hyponatraemia due to
SIADH following TBI is a rare but important complication.It likely results from damage to the pituitary stalk or posterior pituitary causing inappropriate non-osmotic hypersecretion of ADH.First line management of
SIADH is generally fluid restriction, but hypertonic saline may be required in severe cases. Adherence to long-term fluid restriction is challenging. Other options include oral
urea,
vasopressin receptor antagonists and
demeclocycline.While effective, oral
urea is poorly tolerated and
vasopressin receptor antagonists are currently not licensed for use in Australia or the USA beyond 30 days due to insufficient long-term safety data and specific concerns of hepatotoxicity.Demeclocycline is an effective, well-tolerated and safe option for management of chronic hyponatraemia due to
SIADH.