Episodic generalized weakness can occur due to all of the following acute electrolyte disturbances, except: (AIIMS May 2010)
Muscle membrane excitability is affected in a group of disorders referred to as channelopathies. The heart may also be involved, resulting in life-threatening complications.
Channelopathies are diseases caused by disturbed function of ion channel subunits or the proteins that regulate them. These diseases may be either congenital or acquired.
All periodic paralysis start before the age of 25 years except thyrotoxicosis periodic paralysis which can start after 25 years of age.
1). Hypokalemic PP
a. Attack are precipitated by heavy exercise followed by heavy meals & rest.
i. Potassium supplement
ii. Potassium sparing diuretics (Triamterene, Spironolactone)
2). Hyperkalemic PP
a. Attack are precipitated by heavy exercise followed by no meals & rest.
b. Treatment acetazolamide
3). Paramyotonia Congenita. (PC) (Ref. Hariarrison - 18th, Pg- 3506)
a. In PC, the attacks of weakness are cold-induced or occur spontaneously and are mild.
b. Myotonia is a prominent feature but worsens with muscle activity (paradoxical myotonia).
c. This is in contrast to classic myotonia in which exercise alleviates the condition.
d. Cooling of the muscle often dramatically reduces the amplitude of the compound muscle action potentials.
e. PC is inherited as an autosomal dominant condition; voltage-gated sodium channel mutations.
f. Oral administration of glucose or other carbohydrates hastens recovery.
g. Prophylactic treatment. Thiazide, Mexiletine
4. Anderson's Syndrome (Ref. Hariarrison - 18th, Pg- 3506)
a. This rare disease is characterized by episodic weakness, cardiac arrhythmias, and dysmorphic features (short stature, scoliosis, clinodactyly, hypertelorism, small or prominent low-set ears, micrognathia, and broad forehead).
b. The cardiac arrhythmias are potentially serious and life threatening.
c. They include long QT, ventricular ectopy, bidirectional ventricular arrhythmias, and tachycardia.
d.Prophylactic Treatment = Acetazolamide