Episodic muscle tremors in a quarter horse: resemblance to hyperkalemic periodic paralysis.

This research article presents the case of a three-year-old Quarter Horse stallion suffering from episodic muscle tremors and stiffness. The report suggests that this rare equine condition could resemble Hyperkalemic Periodic Paralysis (HYPP), a genetic disorder found in humans.

Summary of the Case

• The horse was presented with a history of generalized muscle tremors and spasms – mainly observed on facial expression muscles, lasting for about 10-15 minutes. These episodes seemed to occur independently of physical exercise.
• In-between attacks, the horse’s condition fluctuated between normality and exhibiting localized muscle tremors in the flank region.
• Diagnostic findings revealed an abnormal increase in plasma potassium levels during an attack – from a resting level of 4.4 to 7.9 mmol/L. Additionally, electromyographic readings showed increased generalized insertion activity and myotonic discharges.

Treatment and Progress

• The horse was treated with Hydrochlorothiazide tablets over a span of nine months, during which he experienced no further attacks. Nonetheless, after discontinuing the medication, sporadic focal muscle tremors were observed again after four months. Two months later, general attacks recommenced.
• The reinitiation of the diuretic treatment did not seem to eliminate a persistent focal flank tremor.

Additional Observations

• Two related horses in the same stable were also reported by the owner to sporadically exhibit generalized muscle twitching.

Horse Condition in Relation to Human Disorders

• The clinical symptoms of the stallion were not synonymous with any other horse condition previously reported.
• However, the authors of the study noted some similarities between these abnormal findings and hyperkalemic periodic paralysis in humans – a genetic disorder associated with episodes of muscle weakness or paralysis, correlating with a rise in the level of potassium in the blood.