Hypokalemic Myopathy in a Dog with Addison's Disease

A  7-year-old spayed female standard poodle with primary signs of lethargy and loss of appetite was diagnosed as having adrenocortical hypofunction based on basal and post-ACTH serum cortisol concentrations of 0.3 and 0.4 µg/dl. Initial blood tests included a serum biochemistry profile and hemogram. Despite normal serum sodium and potassium concentrations (146, reference 139-154, and 5.1 meq/L, reference 3.6-5.5, respectively), the clinical signs and breed predilection suggested atypical Addison's disease, prompting the ACTH stimulation test, the gold standard diagnostic test for hypoadrenocorticism. The dog was treated with 1 intramuscular injection of DOCP at the standard dose of 1 mg/lb. 

The patient developed generalized muscular weakness over the next 2 weeks that also caused a flaccid ventral cervical posture (left). Serum electrolytes at this time showed the sodium at 154 meq/L and potassium at 3.2 meq/L. In-hospital treatment for the presumed hypokalemic myopathy consisted of intravenous 0.9% sodium chloride solution with 50 meq potassium chloride per liter of saline. Prednisone was given at a dose of 0.3 mg/kg/day in order to provide the essential basal glucocorticoid needed while the further use of DOCP was discontinued.* The dog showed dramatic improvement after 24 hours and appeared normal by the second day. The serum sodium and potassium levels at that time were 160 and 3.85 meq/L, respectively. The reexamination 1 week later was normal (right).

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