201. Ion Channel Myotonias, Myotonia Congenita, and Acquired Neuromyotonia Flashcards
What is the cause of myotonia congenita?
Dysfunction in chloride channel on chromosome 7 leading to delayed skeletal muscle relaxation
This condition can lead to significant phenotypic variance, including Thomas and Becker types.
What are the types of ion-channel myotonias?
Paramyotonia congenita (PMC) and potassium-aggravated myotonias (PAMs)
Both are caused by missense mutations of the skeletal muscle voltage-gated sodium channel gene.
What distinguishes PAM from PMC?
PAM leads to myotonia only, while PMC leads to myotonia plus periodic paralysis.
What are the symptoms of acquired neuromyotonia?
Involuntary muscle fiber activity, delayed relaxation, stiffness, ataxia, progressive weakness, muscle cramping
Patients may also experience hyperhidrosis, tachycardia, and weight loss.
How is myotonia congenita diagnosed?
Clinical evaluation, family history, genetic testing, and electromyography (EMG)
EMG typically shows action potentials after myotonic discharges.
What is the role of EMG in diagnosing ion-channel myotonias?
EMG shows rapid repetitive electrical discharges in muscles if the disease state is present.
What is needed to confirm acquired neuromyotonia?
Evidence of continuous muscle contractions and muscle cramps, confirmed by EMG
Serum studies should reveal the presence of an anti–gated potassium channel.
What is the treatment approach for myotonia congenita?
Patient-by-patient basis, early intervention, genetic counseling
High variability in disease severity necessitates individualized therapy.
What lifestyle modification is recommended for patients with PMC and PAM?
Avoid sudden exposure to cold and sudden heavy physical activity.
What dietary consideration should patients with potassium-aggravated myotonias manage?
Potassium intake
Potassium-rich foods can trigger the disorder.
What medications may benefit patients with ion-channel myotonias?
Mexiletine, lamotrigine, thiazide diuretics
Genetic counseling is also recommended.
What is the therapy of choice for acquired neuromyotonia?
Anticonvulsant drugs (phenytoin or carbamazepine)
These drugs help stop abnormal impulses.
What are the anesthesia considerations for patients with myotonias?
Neuromuscular monitoring, maintaining normothermia, avoiding succinylcholine
Shivering can induce myotonic reactions.
What should be avoided during intraoperative management of myotonia patients?
Succinylcholine
It can provoke severe generalized myotonia and possibly malignant hyperthermia.
What is a safe muscle relaxant option for myotonia patients?
Short-acting, non-depolarizing muscle relaxants (e.g., atracurium).
