Laryngeal and pharyngeal dysfunction in horses homozygous for hyperkalemic periodic paralysis.

OBJECTIVE

Evaluate histories, clinical signs, and laboratory data of 69 horses homozygous by DNA testing for hyperkalemic periodic paralysis (HPP).

DESIGN

Cohort study.

SAMPLE POPULATION

69 of 189 horses testing homozygous for HPP between October 1992 and November 1994.

PROCEDURE

Questionnaires addressing signalment, training regimes, medical history, and current status of affected horses were sent to owners, trainers, 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 frequency from mild muscle fasciculations to recumbency and death. Sixty-three of 68 HPP-affected horses were reported to have had stridor associated with exercise, excitement, stress, or episodes of muscle paralysis. Common endoscopic findings in affected horses included pharyngeal collapse, pharyngeal edema, laryngopalatal dislocation, and laryngeal paralysis. Twelve of 27 horses receiving acetazolamide had decreases in stridor while receiving medication.

CLINICAL IMPLICATIONS

Most horses testing homozygous for HPP had clinical signs associated with pharyngeal and laryngeal dysfunction. Hyperkalemic periodic paralysis should be included on a differential list for horses examined for signs of laryngeal or pharyngeal dysfunction or stridor. Treatment with acetazolamide may help to control respiratory tract signs associated with this disease.