Severe Gastrointestinal Disease in a Dog Presenting With Hypoadrenocorticism-Like Electrolyte Derangements Due to Protothecosis.

Protothecosis should be considered when hypoadrenocorticism-like electrolyte derangements accompany chronic gastrointestinal signs.

This case report describes a 3-year-old neutered female Labrador Retriever presenting with acute lethargy, hyporexia, and ataxia, with a prior history of chronic gastrointestinal signs of undetermined etiology. Clinicopathologic evaluation revealed findings closely mimicking hypoadrenocorticism, including severe hyperkalemia, hyponatremia, and a sodium-to-potassium ratio below 14:1. Rather than Addison's disease, the underlying etiology was identified as systemic protothecosis caused by Prototheca bovis, confirmed via histopathology of endoscopic gastrointestinal biopsies and polymerase chain reaction testing. Protothecosis is a rare infection caused by achlorophyllic algae, and the disseminated form in dogs most commonly involves the gastrointestinal tract, eyes, and central nervous system. The proposed mechanism for electrolyte derangements in this case is severe gastrointestinal disease disrupting normal sodium and potassium homeostasis, rather than adrenocortical insufficiency. The dog initially responded to oral antifungal therapy; however, progressive ophthalmologic and neurologic deterioration ultimately led to euthanasia. This is reported as the first documented association between canine protothecosis and severe hyperkalemia, and one of few reports of gastrointestinal disease causing hyperkalemia of this magnitude. Clinicians should consider protothecosis as a differential diagnosis when hypoadrenocorticism-like electrolyte abnormalities are present alongside chronic gastrointestinal signs, particularly when adrenal function testing does not support a diagnosis of Addison's disease.

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