Abstract
This exploratory study aims to create an evidence-based comprehensive characterization of hyperkalemic periodic paralysis (hyperPP). HyperPP is a rare genetic disorder that causes episodes of flaccid paralysis. Disease descriptions in the literature are based upon isolated clinical encounters and case reports. We describe the experience of a large cohort of genetically diagnosed individuals with hyperPP. We surveyed genetically characterized individuals age 18 and over to assess disease comorbidities, diagnostic testing, management, and quality of life issues relevant to hyperPP. Myotonia was reported by 55.8 % of subjects and paramyotonia by 45.3 %. There is a relative risk of 3.6 (p < 0.0001) for thyroid dysfunction compared to the general population. Twenty-five percent of subjects experienced their sentinel attack in the second decade of life. It took an average of 19.4 years and visits to four physicians to arrive at the diagnosis of hyperPP. In addition to limbs and hands being affected during attacks, 26.1 % of subjects reported their breathing musculature was affected and 62.0 % reported their facial muscles were affected. There was a lifelong trend of increasing attack frequency, which was particularly common during childhood and adolescence. Approximately one-third of individuals experienced progressive myopathy. Permanent muscle weakness was evident and worsened during childhood and after age 40. Those with no chronic treatment regimen have a RR of 2.3 for inadequate disease control compared to those taking long-term medications. This study revealed a multitude of heretofore unidentified characteristics of hyperPP, in addition to providing a different perspective on some previously held notions regarding the condition.Electronic supplementary materialThe online version of this article (doi:10.1007/s00415-013-7025-9) contains supplementary material, which is available to authorized users.
Highlights
Hyperkalemic periodic paralysis is an autosomal dominant muscle sodium channelopathy with nearly complete penetrance [1]
The name was later changed to hyperkalemic periodic paralysis in light of the provocative effects of potassium intake as well as the rise in serum potassium levels associated with spontaneous attacks [1]
Findings in our study that add to current knowledge or that counter scientific literature regarding hyperkalemic periodic paralysis (hyperPP) include the following points
Summary
Hyperkalemic periodic paralysis (hyperPP) is an autosomal dominant muscle sodium channelopathy with nearly complete penetrance [1]. In 1957, Gamstorp extensively investigated the condition and named it adynamia episodica hereditaria [3]. Point mutations in the SCN4A gene encoding the alpha subunit of the skeletal muscle voltage-gated sodium channel Nav1.4 lead to defective channel function. This disrupts the normal exchange of ions in skeletal muscles, reducing their ability to contract and resulting in attacks of muscle weakness or paralysis [4, 5]. The condition affects approximately 1 in every 200,000 people [1]. De novo mutations have been reported [6]
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