Respiratory stridor associated with polymyopathy suspected to be hyperkalemic periodic paralysis in four quarter horse foals.

The research article explores a case study of four Quarter Horse foals suffering from upper respiratory stridor, hypothesized to be an effect of a polymyopathy (muscle disorder) speculated to be hyperkalemic periodic paralysis. Various testing methods and treatments were applied to manage the condition, with mixed outcomes.

Participants and Condition

• The subjects of the study were four Quarter Horse foals, aged between 6 days to 2 months. These young horses exhibited a condition called upper airway stridor, which is typically characterized by a harsh, grating sound when breathing primarily during inhalation.
• This was associated with a suspected case of polymyopathy – a disease that affects multiple muscles, considered to be hyperkalemic periodic paralysis (a genetic disorder that causes muscle weakness or paralysis when potassium levels in the blood elevate).

Findings and Diagnosis

• All four foals underwent electromyography, a procedure that assesses the electrical activity of muscles. The examinations revealed spontaneous muscle activity in each of the muscles studied.
• Three of the foals’ dams (mothers), specifically those of foals 1, 3 and 4, presented similar electromyographic findings, suggesting a possible hereditary influence.
• Blood tests performed disclosed increased levels of potassium (hyperkalemia) in foals 1 and 4.
• An endoscopic evaluation identified that the upper airway stridor in foals 1 and 3 was due to laryngeal and pharyngeal collapse or spasm, confirming the physical symptoms with the suspected condition.

Treatment and Outcome

• Acetazolamide, a medication used to treat periodic paralysis, was administered to foals 1, 2, and 3. The owner of foal 4 decided against any treatment.
• The treatment led to improvement in foals 2 and 3, while the untreated foal 4’s condition remained unchanged.
• Foal 1’s condition required further medical intervention, in the form of a tracheostomy (a surgery to create an opening in the neck into the windpipe) and laryngeal surgery, to manage its upper airway stridor.