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Hyperkalemic Periodic Paralysis

What Is It?

  • Hyperkalemic Periodic Paralysis Disease (HYPP) is an inherited muscle disease. It is caused by a hereditary genetic defect that disrupts a protein that forms the sodium ion channel, a tiny gateway in the membrane of muscle cells. The genetic defect disrupts the channel’s normal opening and closing, so that uncontrolled sodium influxes occur. These influxes in turn change the voltage current of muscle cells, causing uncontrolled muscle twitching or profound muscle weakness. High levels of potassium in the blood usually are present when the disruptions in the sodium ion channel occur. At the same time, potassium leaks out of the cell, affecting the voltage current after contraction. The potassium remains in the extracellular fluid, preventing the muscle cell from relaxing.

  • The original genetic defect causing HYPP was a natural mutation that occurred as part of the evolutionary process. The genetic mutation causing HYPP produced a functional, yet altered, sodium ion channel. This gene mutation is not a product of inbreeding. The gene mutation causing HYPP has been found only in descendants of the stallion IMPRESSIVE, AQHA Number 0767246.

  • HYPP is characterized by muscle weakness, twitching (fasciculation) and paralysis.

Dietary and Management Recommendations

  • A horse suspected of being N/H or H/H should be on a low potassium diet (less than 1% in total diet). A DNA test should be used to confirm the status so that appropriate treatment can be administered.

  • The horse should be turned out as much as possible and/or placed on a regular exercise program. Feed oat or grass hay but NOT orchard grass hay, which is high in potassium. It is a good idea to have forage tested for actual potassium content.

  • Do not feed electrolytes containing potassium.
  • Do not use high levels of cane, molasses or bran mashes as these may contain high levels of potassium.

  • For mild episodes:
    • Exercise the horse, either by walking or lunging. Exercise stimulates adrenalin, which helps replace potassium inside the cells. However, use caution, as the horse could stumble and fall while sustaining muscle tremors.

    • Supplement diet with grain (oats, dry corn-oats-barley or light corn syrup) as a source of glucose. Glucose stimulates the release of insulin and promotes potassium uptake by cells.

  • For severe attacks, immediate veterinary attention is necessary.


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