Hypokalemic Periodic Paralysis HypoKPP is a rare inherited muscle disorder which is estimated to occur in only one of , individuals. Because it is inherited there may be several members in a family who have the disorder, which makes it obvious that the one in , figure is a statistical estimate, and does not represent real patients. During severe attacks the patient may be unable to move and even appear unconscious. Even during paralysis the patient is awake and completely aware of their surroundings.
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SCN4A a voltage-gated sodium channel Nav1. This depolarisation propagates to the T-tubules where it triggers the entry of calcium ions via Cav1. This causes contraction tensing of the muscle. Depolarisation of the motor end plate causes potassium ions to leave the muscle cells, repolarising the muscle and closing the calcium channels. Calcium is pumped away from the contractile apparatus and the muscle relaxes. Mutations altering the usual structure and function of these channels therefore disrupts regulation of muscle contraction, leading to episodes of severe muscle weakness or paralysis.
Mutations have been identified in arginine residues making up the voltage sensor of Nav1. This voltage sensor comprises the S4 alpha helix of each of the four transmembrane domains I-IV of the protein, and contains basic residues that only allow entry of the positive sodium ions at appropriate membrane voltages by blocking or opening the channel pore.
In Cav1. These mutations are loss-of-function, such that the channels cannot open normally. As a result, the muscle cannot contract efficiently paralysis. The condition is hypokalemic manifests when potassium is low; not "causing hypokalemia" because a low extracellular potassium ion concentration will cause the muscle to repolarise to the resting potential more quickly, so even if calcium conductance does occur it cannot be sustained.
It becomes more difficult to reach the calcium threshold at which the muscle can contract, and even if this is reached then the muscle is more likely to relax. Because of this, the severity would be reduced if potassium ion concentrations are kept high. In contrast, hyperkalemic periodic paralysis refers to gain-of-function mutations in sodium channels that maintain muscle depolarisation and therefore are aggravated by high potassium ion concentrations.
This condition is inherited in an autosomal dominant pattern but with a high proportion of sporadic cases , which means one copy of the altered gene in each cell is sufficient to cause the disorder. Diagnosis[ edit ] Diagnosis can be achieved through a specialized form of electromyographic EMG testing called the long exercise test.
This test measures the amplitude of a nerve response called the Compound Muscle Action Potential or CMAP for 40 to 50 minutes following a few minutes of exercise. In affected patients, there is a progressive fall in the amplitude of the potential. Besides the patient history or a report of serum potassium low normal or low during an attack, the long exercise test is the current standard for medical testing. Provoking an attack with exercise and diet then trying oral potassium can be diagnostic, but also dangerous as this form of PP has an alternate form known as hyperkalemic periodic paralysis.
The symptoms are almost the same, but the treatment is different. The old glucose insulin challenge is dangerous and risky to the point of being life-threatening and should never be done when other options are so readily available.
The tendency of people with hypokalemic periodic paralysis to get paralyzed when epinephrine is released in "fight or flight" situations further adds to the temptation to misdiagnose the disorder as psychiatric. Avoiding carbohydrate-rich meals, strenuous exercise and other identified triggers, and taking acetazolamide or another carbonic anhydrase inhibitor, may help prevent attacks of weakness.
Some patients also take potassium-sparing diuretics such as spironolactone to help maintain potassium levels. Rapidly absorbed boluses of liquid potassium are generally needed to abort an attack, but some patients also find positive maintenance results with time-released potassium tablets. IV potassium is seldom justified unless the patient is unable to swallow. Daily potassium dosage may need to be much higher than for potassium replacement from simple hypokalemia: mEqs of potassium is often needed to manage daily fluctuations in muscle strength and function.
Normal saline is the preferred IV solution for patients with familial hypokalemic periodic paralysis. Glucose containing solutions may cause weakness. Additionally, the high chloride content can cause a mild acidosis which would be preferred over alkalosis. Prognosis[ edit ] The prognosis for periodic paralysis varies. Overactivity, a diet that is not low in sodium and carbohydrates, or simply an unfortunate gene mutation can lead to a type of chronic, low level weakness called an "abortive attack," or to permanent muscle damage.
Abortive attacks often respond to extra potassium, cutting carbohydrates, getting plenty of rest, increasing doses of medication and gentle daily exercise such as short walks.
Permanent muscle weakness is just what it sounds like: Permanent, irreparable damage to the muscles and associated weakness. Vacuoles and tubular aggregates form in and destroy healthy muscle tissue. This type of damage can typically be observed via a muscle biopsy. Not even anabolic steroids can repair this type of muscular damage. Patients often report muscle pain and cognitive problems during attacks. Medical literatures states that muscle strength is normal between attacks, but patients often report that their baseline strength is in fact lower than that of healthy individuals.
Patients and caregivers should take extreme caution with all new drugs and treatment plans. She also described the glucose challenge test used in diagnosing hypokalaemic periodic paralysis and the use of intravenous potassium in its treatment.
What Is Hypokalemic Periodic Paralysis and How Is It Treated?
How common is hypokalemic periodic paralysis? Hypokalemic periodic paralysis hypoPP or hypoKPP is a rare disorder in which a person experiences episodes of painless muscle weakness and often paralysis. This form of paralysis is associated with low potassium levels. Are there different types of hypokalemic periodic paralysis? There are two types of hypoPP: Paralytic: This form is most common. In the paralytic form, intermittent, temporary episodes of muscle weakness or paralysis are experienced.
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The medical name for low potassium level is hypokalemia. HypoPP is one of a group of genetic disorders that includes hyperkalemic periodic paralysis and thyrotoxic periodic paralysis. HypoPP is the most common form of periodic paralysis. It affects males more often. Causes HypoPP is congenital. This means it is present at birth.