Hyperkalemic periodic paralysis (HYPP), also known as Impressive Syndrome, is an inherited autosomal dominant disorder which affects sodium channels in muscle cells and the ability to regulate potassium levels in the blood. It is most commonly associated with horses, but also occurs in humans, where it is also called Gamstorp episodic adynamy.
* Weakness/paralysis o Most commonly located in the shoulders and hips o Arms and legs may also be involved o Occurs intermittently o May occur on awakening o May be triggered by rest after exercise o May be triggered by fasting o May be triggered by exposure to cold o May be triggered by eating small amounts of potassium o Usually lasts for less than 2 hours * Return to normal strength between attacks * Normal alertness during attacks (no confusion or loss of consciousness)
The cause of hyperkalemic periodic paralysis is believed to be a genetic muscle disease. In most cases it is inherited directly (from parent to child); in other cases, it occurs randomly in a family group. The disorder involves attacks of muscle weakness or paralysis, alternating with periods of normal muscle function. Attacks usually begin in early childhood. Multiple daily attacks are possible. Attacks typically last only 1 to 2 hours, but can sometimes last as long as a day. They tend to occur while resting after exercise or exertion. Attacks may also be triggered by exposure to cold, or by eating small amounts of potassium.
Treatment prevents attacks of weakness.
Sometimes attacks disappear later in life on their own. However, chronic attacks generally result in progressive muscle weakness that is present even between attacks. Hyperkalemic periodic paralysis responds well to treatment. Treatment may prevent, and may even reverse, progressive muscle weakness.
The goals of treatment are relief of acute symptoms and prevention of further attacks. Attacks are seldom severe enough to require emergency treatment. However, weakness can become worse with repeated attacks, so treatment to prevent the attacks should occur as soon as possible. Glucose or other carbohydrates (sugars) given during an attack may reduce the severity. Intravenous calcium or diuretics such as furosemide may be needed to stop sudden attacks. Intravenous glucose and insulin cause potassium to move into the cell and may reduce weakness without a loss of total body potassium. A high-carbohydrate diet may be recommended.