Neuromuscular Diseases and Disorders

Question 1

What is the inheritance pattern of hypokalemic periodic paralysis? Hyperkalemic periodic paralysis?

Answer 1

autosomal dominant for both

Question 2

What precipitates hyperkalemic periodic paralysis?

Answer 2

dehydration (exercise and fasting)

potassium-rich foods

Question 3

What precipitates hypokalemic periodic paralysis?

Answer 3

hyperglycemia (insulin burst leads to hypokalemia)

hyperventilation (alkalosis leads to hypokalemia)

viral illness

rest following exercise

Question 4

Is an extremity affected by a stroke more or less sensitive to non-depolarizing muscle relaxants?

Answer 4

less sensitive due to extrajunctional receptors

*true of all upper motor neuron conditions*

Question 5

Is cerebral palsy a contraindication for succinylcholine?

Answer 5

No

*CP patients do not develop extrajunctional receptors*

Question 6

Is MS a contraindication to succinylcholine?

Answer 6

a relative contraindication, more absolute in the presence of significant paresis

Question 7

Why is succinylcholine contraindicated in Duchenne’s muscular dystrophy? Myotonic dystrophy? ALS? Guillain Barre syndrome?

Answer 7

DMD: hyperkalemia from disrupted myocyte membrane

MyoD: persistent contractures preventing intubation and ventilation

ALS and GBS: hyperkalemia from extrajunctional receptors

Question 8

What should be avoided to prevent sustained contractures in patients with myotonic dystrophy?

Answer 8

succinylcholine

anti-cholinesterases (e.g., neostigmine)

hypothermia

Question 9

Does myasthenia gravis affect skeletal muscle, smooth muscle, or both?

Answer 9

only skeletal muscle

Question 10

How do you distinguish between weakness from worsening myasthenia and a cholinergic crisis?

Answer 10

edrophonium challenge (e.g., tensilon test)

Question 11

Which factors increase the risk of post-op ventilation in pateints with myasthenia gravis?

Answer 11

disease duration > 6 years

vital capacity < 2.9 L

pyridostigmine dose > 750 mg/day

concomitant respiratory disease

Question 12

How are infants of mothers with myasthenia gravis affected?

Answer 12

They can have myasthenia for up to 3 weeks.

Question 13

How does Eaton-Lambert myasthenia syndrome affect sensitivity to muscle relaxants?

Answer 13

More sensitive to succinylcholine due to upregulated AChRs

More sensitive to non-depolarizing agents due to less ACh to compete with