RT Book, Section
A1 Douglas, Vanja C.
A1 Aminoff, Michael J.
A2 Papadakis, Maxine A.
A2 McPhee, Stephen J.
A2 Rabow, Michael W.
A2 McQuaid, Kenneth R.
SR Print(0)
ID 1193129684
T1 Periodic Paralysis Syndromes
T2 Current Medical Diagnosis & Treatment 2023
YR 2023
FD 2023
PB McGraw-Hill Education
PP New York, NY
SN 9781264687343
LK accessmedicine.mhmedical.com/content.aspx?aid=1193129684
RD 2024/04/23
AB Periodic  paralysis  may  have  a  familial  (dominant  inheritance)  basis.  The  syndromes  to  be  described  are  channelopathies  that  manifest  as  abnormal,  often  potassium-sensitive,  muscle-membrane  excitability  and  lead  clinically  to  episodes  of  flaccid  weakness  or  paralysis,  sometimes  in  association  with  abnormalities  of  the  plasma  potassium  level.  Strength  is  initially  normal  between  attacks,  but  progressive  myopathic  weakness  may  develop  in  up  to  one-third  of  patients  as  they  age.  Mutations  in  genes  encoding  three  ion  channels  (CACNA1S,  SCN4A,  and  KCNJ18)  account  for  most  cases.  Hypokalemic  periodic  paralysis  is  characterized  by  attacks  that  tend  to  occur  on  awakening,  after  exercise,  or  after  a  heavy  meal  and  may  last  for  several  days.  Patients  should  avoid  excessive  exertion.  A  low-carbohydrate  and  low-salt  diet  may  help  prevent  attacks.  An  ongoing  attack  may  be  aborted  by  potassium  chloride  given  orally  or  by  intravenous  drip,  provided  the  ECG  can  be  monitored  and  kidney  function  is  satisfactory.  In  young  Asian  men,  it  is  commonly  associated  with  hyperthyroidism  and  has  been  related  to  polymorphism  in  the  CACNA1S  gene;  treatment  of  the  endocrine  disorder  prevents  recurrences.  A  nonselective  beta-adrenergic  blocker  may  prevent  attacks  until  the  endocrine  abnormality  has  been  treated.  In  hyperkalemic  periodic  paralysis,  which  is  mostly  associated  with  mutations  in  the  SCN4A  gene,  attacks  also  tend  to  occur  after  exercise  but  usually  last  for  less  than  1  hour.  They  may  be  terminated  by  intravenous  calcium  gluconate  (1–2  g)  or  by  intravenous  diuretics  (furosemide,  20–40  mg),  glucose,  or  glucose  and  insulin.  Normokalemic  periodic  paralysis  is  similar  clinically  to  the  hyperkalemic  variety,  but  the  plasma  potassium  level  remains  normal  during  attacks.  Several  randomized  trials  support  the  use  of  dichlorphenamide  (50–100  mg  orally  twice  daily)  for  prevention  of  attacks  in  both  hyperkalemic  and  hypokalemic  periodic  paralysis;  acetazolamide  (250–750  mg  orally  daily)  is  also  effective.  Chlorothiazide  may  also  be  used  to  prevent  attacks  in  hyperkalemic  periodic  paralysis.