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Genetic and Rare Diseases Information Center (GARD)

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Normokalemic periodic paralysis


Other Names for this Disease
  • Normokalemic PP
  • NormoKPP
  • Periodic paralysis type 3
  • Potassium-sensitive normokalemic periodic paralysis
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Overview



What is normokalemic periodic paralysis?

What are the signs and symptoms of normokalemic periodic paralysis?

How might normokalemic periodic paralysis be treated?


What is normokalemic periodic paralysis?

Normokalemic periodic paralysis (NormoKPP) is an inherited muscle disorder characterized by episodic attacks of muscle weakness.[1][2] It was initially considered a distinct condition, but most physicians now consider it to be a variant form of hyperkalemic periodic paralysis. People with hyperkalemic periodic paralysis have increased potassium levels during an attack; people with the normokalemic form do not experience any change in their potassium levels during weakness, but most grow weak when given potassium.[3] Studies have shown that both forms of the condition are caused by mutations in the SCN4A gene and it is inherited in an autosomal dominant manner.[2] The goals of treatment are to relieve acute symptoms and prevent further attacks.[3]
Last updated: 9/12/2012

What are the signs and symptoms of normokalemic periodic paralysis?

Normokalemic periodic paralysis (normoKPP) is thought to be a variant of hyperkalemic periodic paralysis. Some people with hyperkalemic periodic paralysis have increased levels of potassium in their blood (hyperkalemia) during attacks, while in other cases, attacks are associated with normal blood potassium levels (normokalemia). Ingesting potassium can trigger attacks in affected individuals, even if blood potassium levels do not go up.[4] It has been reported that the potassium-sensitivity in normoKPP resembles hyperkalemic periodic paralysis, whereas other features resemble hypokalemic period paralysis.[5]

The condition causes episodes of extreme muscle weakness that usually begin in infancy or early childhood. These episodes often involve a temporary inability to move muscles in the arms and legs. Factors that may trigger attacks may include rest after exercise; ingesting potassium-rich foods or drinks; stress; fatigue; fasting; and/or exposure to cold temperatures.[4][6][7] Muscle strength generally improves between attacks, although many affected people continue to have mild stiffness (myotonia) in some muscles.[4]
Last updated: 9/12/2012

How might normokalemic periodic paralysis be treated?

Although much progress has been made in understanding periodic paralysis, there is currently no consensus on treatment and effective treatment options are limited.[8] Furthermore, likely because many experts do not consider normokalemic periodic paralysis to be a distinct condition (it is thought to be a variant of hyperkalemic periodic paralysis), there is little information available in the medical literature regarding this specific variant of the rare condition.

The limited research that has been published has suggested that carbonic acid anhydrase inhibitors may reduce attack frequency and severity in periodic paralysis. However, there has not been sufficient information in terms of which of the carbonic acid anhydrase inhibitors (dichlorphenamide or acetazolamide) is more effective or has fewer side effects.[8]

Experts generally agree that affected individuals should avoid the triggers of attacks through lifestyle and dietary modification.[9] It has been reported that people with the hyperkalemic form can prevent attacks by eating frequent meals rich in carbohydrates and low in potassium and by avoiding fasting, strenuous activity, and exposure to cold.[6] Symptoms of individuals who are normokalemic during attacks may be improved by exercising.[9]
Last updated: 9/12/2012

References
  1. Young-Wha Song et al. Normokalemic periodic paralysis is not a distinct disease. Muscle and Nerve. August 2012; epub:
  2. S. Vicart et al. New mutations of SCN4A cause a potassium-sensitive normokalemic periodic paralysis. Neurology. December 2004; 63(11):2120-2127.
  3. What is periodic paralysis?. Periodic Paralysis International. June 21, 2011; http://hkpp.org/. Accessed 9/11/2012.
  4. Hyperkalemic periodic paralysis. Genetics Home Reference. April 2007; http://ghr.nlm.nih.gov/condition/hyperkalemic-periodic-paralysis. Accessed 9/11/2012.
  5. Karin Jurkat-Rott and Frank Lehmann-Horn. Hyperkalemic Periodic Paralysis Type 1. GeneReviews. May 31, 2011; http://www.ncbi.nlm.nih.gov/books/NBK1496/. Accessed 9/12/2012.
  6. Michael Rubin. Periodic paralysis. Merck Manuals. January 2008; http://www.merckmanuals.com/home/childrens_health_issues/muscular_dystrophies_and_related_disorders/periodic_paralysis.html#v732922. Accessed 9/12/2012.
  7. Patrick F. Chinnery, Timothy J. Walls, Michael G. Hanna, David Bates, Peter R. W. Fawcett. Normokalemic periodic paralysis revisited: Does it exist?. Annals of Neurology. August 2002;
  8. Sansone V, Meola G, Links TP, Panzeri M, Rose MR. Treatment for periodic paralysis. Cochrane Database Syst Rev. January 2008; 23(1):
  9. S. L. Venance et al. The primary periodic paralyses: diagnosis, pathogenesis and treatment. Brain. 2006; 129:8-17.