Periodic paralysis

Periodic paralysis
Classification and external resources
Specialty neurology
ICD-10 G72.3
ICD-9-CM 359.3
MeSH D010245

Periodic paralysis (also known as Myoplegia paroxysmalis familiaris) is a group of rare genetic diseases that lead to weakness or paralysis (rarely death) from common triggers such as cold, heat, high carbohydrate meals, not eating, stress or excitement and physical activity of any kind. The underlying mechanism of these diseases are malfunctions in the ion channels in skeletal muscle cell membranes that allow electrically charged ions to leak in or out of the muscle cell, causing the cell to depolarize and become unable to move (a channelopathy).

The symptoms of periodic paralysis can also be caused by hyperthyroidism, and are then labeled thyrotoxic periodic paralysis; however, if this is the underlying condition there are likely to be other characteristic manifestations, enabling a correct diagnosis.

Types

Periodic paralysis is an autosomal dominant myopathy with considerable variation in penetrance, leading to a spectrum of familial phenotypes (only one parent needs to carry the gene mutation to affect the children, but not all family members who share the gene are affected to the same degree). Specific diseases include:

Diagnosis

This disease is unusually difficult to diagnose. Patients often report years of wrong diagnosis and treatments that made them worse instead of better. Part of this may be that migraines are present in up to 50% of patients and can cause a confusing array of symptoms including headaches, speech difficulties and visual, auditory or sensory auras. DNA testing is available for only a half dozen common gene mutations, while dozens of known mutations are possible but are not routinely tested. Electromyography (EMG) findings are not specific but the McManis Protocol, also called the Compound Muscle Amplitude Potential test (CMAP)can be used by a skilled neurologist capable of utilizing the EMG, which can give assistance in diagnosing several of these PP disorders. The old glucose/insulin provocative testing can cause life-threatening symptoms and should not be used.

Also of note is that potassium levels do not have to range outside of normal limits to cause serious, even life-threatening paralysis. These diseases are not the same as having a very low level of potassium (hypokalemia) or high potassium (hyperkalemia) and must not be treated as such. The total body store of potassium is usually normal; it is just in the wrong place.

Treatment

Treatment of the periodic paralyses may include carbonic anhydrase inhibitors (such as acetazolamide, methazolamide or dichlorphenamide), taking supplemental oral potassium chloride and a potassium-sparing diuretic (for hypos) or avoiding potassium (for hypers), thiazide diuretics to increase the amount of potassium excreted by the kidneys (for hypers), and significant lifestyle changes including tightly controlled levels of exercise or activity. However, treatment should be tailored to the particular type of periodic paralysis.[1][2][3]

Treatment of periodic paralysis in Andersen-Tawil syndrome is similar to that for other types. However, Pacemaker insertion or an implantable cardioverter-defibrillator may be required to control cardiac symptoms.[4]

Prognosis

While the disability can range from minor, occasional weakness to permanent muscle damage, inability to hold a normal job and use of a powerchair, most people function fairly well with drugs and lifestyle changes.

References

  1. ↑ Kim, SJ; Lee, YJ; Kim, JB (Jan 2010). "Reduced expression and abnormal localization of the KATP channel subunit SUR2A in patients with familial hypokalemic periodic paralysis". Biochemical and Biophysical Research Communications. 391: 974–8. doi:10.1016/j.bbrc.2009.11.177. PMID 19962959.
  2. ↑ Kim, JB; Kim, MH (Dec 2007). "The Genotype and Clinical Phenotype of Korean Patients with Familial Hypokalemic Periodic Paralysis". J Korean Med Sci. 22: 946–51. doi:10.3346/jkms.2007.22.6.946.
  3. ↑ Lee, GM; Kim JB (June 2011). "Hyperkalemic periodic paralysis and paramyotonia congenita caused by a de novo mutation in the SCN4A gene". Neurology Asia. 16 (2): 163–6.
  4. ↑ Kim, JB; Chung, KW (Dec 2009). "Novel de novo Mutation in the KCNJ2 gene in a Patient with Andersen-Tawil Syndrome". Pediatric Neurology. 41 (6): 464–466. doi:10.1016/j.pediatrneurol.2009.07.010. PMID 19931173.
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