Table 23–9_

CURRENT Diagnosis &Treatment: Neurology, 3e >Diseases of Muscle
John C.M. Brust+
Table 23–9.Channelopathies: clinical findings and treatment.
Hypokalemic Periodic
Paralysis
Hyperkalemic Periodic
Paralysis
Paramyotonia Congenita
Myotonia Congenita
(Thomsen)
Generalized Myotonia
(Becker)
Malignant Hyperthermia
Inheritance Autosomal dominant Autosomal dominant Autosomal dominant Autosomal dominant Autosomal recessive Autosomal dominant
Ion channel defect
Type 1 = calcium channel
Type 2 = sodium channel
Sodium channel Sodium channel Chloride channel Chloride channel Calcium channel
Onset Puberty to third decade First decade First decade Childhood Childhood All ages
Clinical findings
• Episodic attacks of
weakness (presence,
typical duration, severity)
Present; >2 h; often
severe
Present; <2 h; seldom
severe
May be present; >2 h;
seldom severe
Absent Absent Absent
• Serum CK level during
attack
Normal or mildly elevated Elevated Elevated Usually normal Mildly elevated Markedly elevated
• Myotonia Confined to eyelids May be present Present Prominent Prominent Absent
• Muscle hypertrophy Absent Rarely present Present Present Present Absent
• Precipitating factors
Carbohydrate load,
postexercise period,
pregnancy, emotional
stress, cold
Postexercise period,
fasting, pregnancy,
emotional stress, cold
During exercise, cold,
pregnancy, emotional
stress
“Warming up effect,” a
postexercise period,
emotional stress,
pregnancy, anesthetics
“Warming up effect,” a
postexercise period,
emotional stress,
pregnancy, anesthetics
Anesthetics, (increased
prevalence in
dystrophinopathies and
central core myopathy)
Treatment
Potassium chloride, 0.25
mEq/kg PO (may repeat
every 30 min until
weakness subsides)
Avoid IV potassium
because of risk of
uncontrollable
hyperkalemia
Ingestion of glucose-rich
carbohydrates
Inhalation of a β-
adrenergic agent
(albuterol)
Thiazide diuretic (eg,
hydrochlorothiazide, 25
mg) may also abort an
attack
Glucose for severe cases
Mexiletine for myotonia;
begin 150 mg PO 2 times
a day, to maximum of
1200 mg/d
Mexiletine for myotonia;
begin 150 mg PO 2 times
a day, to maximum of
1200 mg/d
Phenytoin, 300 mg/day or
quinine sulfate, 200–300
mg/d, is also useful.
Same as for myotonia
congenita
Dantrolene
Discontinuation of
anesthesia
Correction of acid-base
disturbances
Management of
myoglobinuric renal failure
Prophylaxis
Acetazolamide; titrate up
to 250 mg 3 times a day
Dichlorphenamide, 25 mg
3 times a day
Acetazolamide; titrate up
to 250 mg 3 times a day
Avoidance of precipitants
Avoidance of precipitants Avoidance of precipitants Avoidance of precipitants Avoidance of precipitants
Avoidance of precipitants
CK = creatine kinase; PO = orally (by mouth); IV = intravenous.
a ”Warming up effect” refers to myotonia that is worse on initiation of exercise, although ameliorated by the increasing vigor of movements.

Date of download: 11/23/22 from AccessMedicine: accessmedicine.mhmedical.com, Copyright © McGraw Hill. All rights reserved.