What is your diagnosis? Marked hyperchloremia in a dog

Area of Science:

• Veterinary Neurology
• Clinical Toxicology
• Canine Medicine

Background:

• A 5-year-old Cavalier King Charles Spaniel presented with progressive paresis.
• The dog had a history of urolithiasis and was treated with potassium citrate capsules for 2 years.
• Initial diagnostic workup, including advanced imaging, did not reveal the cause of the neurological signs.

Observation:

• Neurologic examination, spinal radiography, and MRI revealed no causative lesions.
• Clinical chemistry showed marked hyperchloremia (179 mmol/L) and a negative anion gap (-50.4 mmol/L).
• Serum bromide concentration was critically elevated at 400 mg/dL.

Findings:

• Analysis of the compounded potassium citrate capsules revealed a mean bromide concentration of 239 mg/capsule.
• The severe hyperchloremia and negative anion gap were attributed to bromide toxicity.
• The toxicity was likely caused by the pharmacy inadvertently using bromide instead of citrate.

Implications:

• This case underscores the critical importance of accurate pharmaceutical compounding and quality control.
• It highlights the need for clinicians to consider medication formulation errors as a cause of unexpected clinical signs.
• Awareness of common laboratory analyte interferences and pursuing logical diagnostic pathways are crucial for accurate diagnosis and treatment, even with seemingly straightforward patient histories.