Diagnosis and treatment of abnormal antidiuretic hormone secretion syndrome (SIADH) secondary to head trauma in dog

Abnormal antidiuretic hormone secretion syndrome (SIADH) is a rare hormonal disorder in dogs because antidiuretic hormone (ADH) is not inhibited by hypotonic extracellular fluid, resulting in water retention and dilutive hyponatremia. Clinically, this disorder is characterized by severe hyponatremia, low osmotic pressure, inappropriate urine concentration, and high urinary sodium excretion. Hypotonic hyponatremia has been widely described as the most common electrolyte imbalance in the hospital setting. At the same time, SIADH is known to be the most common cause of symptomatic hyponatremia and is a significant contributor to morbidity and mortality.
Diagnostic criteria for SIADH include hyponatremia (<140mmol/L[<140mEq/L]), hypoosmotic pressure (<290mmol/kg[<290mOsm/kg]), urinary hyperostosis (>100mmol/kg[>100mOsm/kg]), and elevated urinary sodium concentration (>20mmol/kg[> > 20mEq/L]), other diagnostic criteria include regular hydration, and normal renal, adrenal, and thyroid function. This case had significant hyponatremia (124mmol/L) and low osmotic pressure (253.5mOsm/kg). Although urine osmotic pressure and sodium concentration could not be obtained due to the limitation of the urinalysis equipment, combined with the history and physical examination, the possibility of other diseases was very low, and a preliminary diagnosis of SIADH was made. At the same time, we can easily suspect the disease through the differential diagnosis list of hyponatremia (table below).
Abnormal antidiuretic hormone secretion syndrome (SIADH) is a rare hormonal disorder in dogs because antidiuretic hormone (ADH) is not inhibited by hypotonic extracellular fluid, resulting in water retention and dilutive hyponatremia. Clinically, this disorder is characterized by severe hyponatremia, low osmotic pressure, inappropriate urine concentration, and high urinary sodium excretion. Hypotonic hyponatremia has been widely described as the most common electrolyte imbalance in the hospital setting. At the same time, SIADH is known to be the most common cause of symptomatic hyponatremia and is a significant contributor to morbidity and mortality.
Diagnostic criteria for SIADH include hyponatremia (<140mmol/L[<140mEq/L]), hypoosmotic pressure (<290mmol/kg[<290mOsm/kg]), urinary hyperostosis (>100mmol/kg[>100mOsm/kg]), and elevated urinary sodium concentration (>20mmol/kg[> > Although this syndrome is primarily associated with brain injury, lung pathology, malignancy, or the use of certain drugs in the breed, it has little reference in the veterinary literature, so its prevalence and impact in small animals are not well defined. The syndrome, in this case, appears after head trauma, so it is highly suspected to be related to brain injury.
The treatment of SIADH, on the one hand, is to control the primary disease; on the other, it is to treat concurrent hyponatremia. In this case, the primary disease may be intracranial injury or even infection due to head trauma. Furosemide, 1mg/kg/QD.po, was administered to control brain edema. Amoxicillin potassium clavulanate was the antibiotic of choice, but unfortunately, this drug cannot be administered intravenously and may not achieve the desired concentration of CSF drug. Combined antibiotic administration with intravenous ampicillin (22mg/kg, iv,q6h) is a better option. Cefotaxime (20-40mg/kg,iv,q6h) and metronidazole (15mg/kg,iv at first, then 7.5mg/kg,iv,q8h, or 10-15mg/kg,po,q8h). Antibiotics should be given intravenously for 3-5 days to achieve peak blood concentration in CSF and continued orally for four weeks after recovery.
Hyponatremia is treated to correct osmotic pressure and restore average cell volume through intravenous fluid therapy, water restriction, or both to increase the ratio of sodium to water in the extracellular fluid. Asymptomatic animals with hyponatremia are best treated conservatively. Lactate Ringer’s solution or Ringer’s solution can be used for mild hyponatremia (>130mmol/kg) and normal saline for more severe hyponatremia (<130mmol/kg). Fluid and electrolyte balance should be gradually restored within 24 to 48h, and serum electrolyte concentrations and central nervous system symptoms of the animal should be assessed regularly. The more acute and severe the hyponatremia, the more slowly the serum sodium concentration should be restored to prevent central nervous system damage. Furosemide 0.2-1mg/kg IV and maintenance frequency saline may also be used. Furosemide is a loop diuretic with sodium-raising activity. It can proportionally discharge more water than sodium to control and correct hyponatremia. Still, caution must be exercised with diuretics, and hypertonic solutions as this may increase plasma sodium concentration. They lead to permanent brain damage (osmotic demyelination syndrome).
Hyponatremia (<140mmol/L) was reported in about 25% of canine patients with SIADH in veterinary hospitals, with a mortality rate of 13.7% compared with 4.4% in canine patients with normal sodium levels. The prognosis depends mainly on the primary disease’s severity and hyponatremia’s severity. 20mEq/L]), other diagnostic criteria include regular hydration and normal renal, adrenal, and thyroid function. This case was presented with significant hyponatremia (124mmol/L) and low osmotic pressure (253.5mOsm/kg). Although urine osmotic pressure and sodium concentration could not be obtained due to the limitation of the urinalysis equipment, combined with the history and physical examination, the possibility of other diseases was very low, and a preliminary diagnosis of SIADH was made. At the same time, we can easily suspect the illness through the differential diagnosis list of hyponatremia (Table below).