LARYNGEAL AND PHARYNGEAL DYSFUNCTION IN HORSES HOMOZYGOUS FOR HYPERKALEMIC PERIODIC PARALYSIS

Objective-Evaluate histories, clinical signs, and laboratory data of 6 9 horses homozygous by DNA testing for hyperkalemic periodic paralysis (HPP). Design-Cohort study. Sample Population-69 of 189 horses testin g homozygous for HPP between October 1992 and November 1994. Procedure -Questionnaires addressing signalment, training regimes, medical histo ry, and current status of affected horses were sent to owners, trainer s, or attending veterinarians. Data from completed questionnaires were tabulated and evaluated, using descriptive statistics. Results-Sixty- nine (37%) of 189 questionnaires were completed and returned. Clinical episodes of muscle weakness or paralysis varied in severity and frequ ency from mild muscle fasciculations to recumbency and death. Sixty-th ree of 68 HPP-affected horses were reported to have had strider associ ated with exercise, excitement, stress, or episodes of muscle paralysi s. Common endoscopic findings in affected horses included pharyngeal c ollapse, pharyngeal edema, laryngopalatal dislocation, and laryngeal p aralysis. Twelve of 27 horses receiving acetazolamide had decreases in strider while receiving medication. Clinical Implications-Most horses testing homozygous for HPP had clinical signs associated with pharyng eal and laryngeal dysfunction. Hyperkalemic periodic paralysis should be included on a differential list for horses examined for signs of la ryngeal or pharyngeal dysfunction or strider. Treatment with acetazola mide may help to control respiratory tract signs associated with this disease.