Myelinolysis After Correction of Hyponatremia in Two Dogs

Abstract

Two dogs developed delayed neurological deterioration after rapid correction of severe hyponatremia. Sequential magnetic resonance imaging showed the development of lesions in the thalamus. One dog was necropsied, and the lesions were characterized by myelinolysis with sparing of axons and neurons. The second dog gradually recovered n humans, rapid correction of chronic hyponatremia by I upward shifts in serum sodium concentrations exceeding 12 mmol/L in 24 hours commonly leads to delayed neurological deterioration. This deterioration is associated with lesions of well-demarcated myelin loss, affecting the pons and other sites in the brain (central pontine myelinolysis).',' Neither the genesis of the lesions nor the reason for their peculiar neuroanatomic distribution is ~nderstood,~ but recent advances in identifying antemortem lesions by magnetic resonance imaging (MRI) suggest that the condition is more common in humans than once believed'~~ and is not uniformly fatal.'-* Similar clinical signs and lesions occur after rapid correction of experimental hyponatremia in a variety of animal species,'-" including dogs." We report the delayed development of neurological signs and extrapontine (predominantly thalamic) lesions after rapid correction of spontaneous hyponatremia in 2 dogs. In 1 patient, postmortem examination confirmed the focal loss of myelin and degeneration of glia in the central thalamic nuclei and rostra1 commissure, with preservation of neurons and axons. The other dog recovered with no residual neurological deficits. Our experience with these patients highlights the need for gradual correction of profound hyponatremia in the clinical setting. Case Reports Dug OneA 4-year-old female English Setter dog developed lethargy after a history of weight loss of several weeks' duration. At physical examination, the 12-kg dog had a temperature of 97°F (36.1°C), a pulse of48 beats per minute, and a respiratory rate of 20 breaths per minute. She was thin and depressed, had pale mucous membranes and labored breathing, and was approximately 5% dehydrated. A complete blood count (CBC) showed neutrophilia with a left shift. Se- (0 'Brien, Kroll, Covert) rum biochemical abnormalities included profound hyponatremia, hypochloremia, hypo-osmolality, hyperkalemia, hyperglycemia, and azotemia (Table 1). An electrocardiogram (EKG) showed no P waves and a T wave deflection of greater than 1/4 of the R wave in lead 11. A tentative diagnosis of hypoadrenocorticism was reached, and an adrenocorticotropic hormone (ACTH) challenge test was performed. From the Departments of Veterinary Medicine and SurgeryThe dog was treated with amoxicillin (250 mg PO BID), dexamethasone ( 1 mg/kg intravenously), and intravenous 0.9% sodium chloride (NaCI) at a rate of 6 1 mL/h. During the first day of hospitalization, the dog's attitude improved dramatically. Her body temperature and heart rate returned to normal; however, watery diarrhea was noted. On day two, the dexamethasone dose was decreased to 0.25 mg/kg, amoxicillin was continued, an...

Hydrocortisone in the management of acute hypoadrenocorticism in dogs: a retrospective series of 30 cases

“…It is currently recommended that correction of hyponatraemia should not exceed 10 to 12 mmol/L/day or 0·5 mmol/L/hour (O'Brien et al . , Brady et al . , Churcher et al .…”

“…A potential adverse effect of treatment can result from the rapid correction of hyponatraemia with subsequent development of osmotic demyelination syndrome, which can be fatal, and has been reported in dogs with hypoadrenocorticism and other disorders associated with hyponatraemia (O'Brien et al . , Brady et al . , Churcher et al .…”

Hypoadrenocorticism

“…In patients with hypoadrenocorticism, 0.9% saline is traditionally recommended as the most appropriate fluid for emergency treatment because of hyponatremia and hyperkalemia; however disadvantages include the tendency for 0.9% saline to be acidifying and the potential concern of increasing the sodium concentration too rapidly, which can theoretically result in delayed central pontine myelinosis (O'Brien, 1994;Brady et al, 1999; see Chapter 1). An IV bolus of a synthetic colloid such as hetastarch (5 mL/kg over 30 minutes) should be considered in hypotensive patients that are hypoproteinemic (total protein < 4.5 g/dL).…”

Syndrome Of Inappropriate Antidiuretic Hormone

“…12 Serum sodium should not increase with treatment by more than 12 mEq/L/day (0.5 mEq/L/hr). When hyponatremia may have been present for more than 24 to 48 hours, care must be taken to prevent central pontine myelinolysis, an osmotically induced demyelination.…”