Laryngospasm, dysphagia, and emaciation associated with hyperkalemic periodic paralysis in a horse.

An 18-month-old Quarter Horse gelding was examined because of weight loss and dysphagia of 1 month's duration. Clinical signs included lethargy, dehydration, ptyalism, and probable aspiration pneumonia. Severe dyspnea and cyanosis were evident after mild exercise. Endoscopy revealed laryngospasm and pharyngospasm. Because clinical signs and endoscopic findings were suggestive of hyperkalemic periodic paralysis (HPP), acetazolamide treatment was instituted. Marked improvement was observed within 48 hours. The horse was determined to be homozygous for HPP. It is likely that this horse's dysphagia, with resultant weight loss and aspiration pneumonia, were clinical manifestations and consequences of HPP. Regardless of age and serum potassium concentration, HPP should be considered as a differential diagnosis for pharyngeal and laryngeal abnormalities and dysphagia in horses with Quarter Horse breeding.