Neuromuscular disorders

Question 1

What does “dying back” refer to?

Answer 1

“Dying back” refers to a process in which the longest nerve fibers are injured and die.

Question 2

What is Wallerian degeneration?

Answer 2

Wallerian degeneration happens to an axon after it has been cut off from its cell body.
- The distal end of the cut axon degenerates.

Question 3

Define entrapment neuropathy.

Answer 3

Entrapment neuropathy is a condition where a nerve is caught between tougher tissues, contributing to chronic irritation and damage.

Question 4

What is the most common site of nerve entrapment?

Answer 4

The carpal tunnel of the wrist is the most common site of nerve entrapment (in this case the median nerve).

Question 5

What is meralgia paresthetica?

Answer 5

Meralgia paresthetica is entrapment of the lateral femoral cutaneous nerve at the level of the inguinal ligament.

Question 6

What is Charcot-Marie Tooth?

Answer 6

Charcot-Marie Tooth is a family of hereditary neuropathies that usually begin to show clinical signs in late childhood and adolescence and progress slowly.

Question 7

What is LEMS?

Answer 7

• It is an uncommon autoimmune condition characterized by weakness of hip girdle muscles with decreased reflexes.
• Autonomic instability is common.
• It often accompanies small cell cancer but can be idiopathic.
• There are usually autoantibodies against voltage-gated calcium channels.
• Strength increases with sustained or repeated contraction (this is different from myasthenia gravis).

Question 8

What is a paraneoplastic syndrome?

Answer 8

A paraneoplastic syndrome refers to remote effects of a tumor.
- Most often it represents a condition in which antibodies directed at a tumor damage other tissues of the body.

Question 9

What is a nerve conduction study?

Answer 9

• Nerve conduction studies evaluate the amplitude of response and speed of conduction along the fastest, largest peripheral nerve fibers.
• Damage to these fibers (especially the myelin sheath) will slow conduction, most severely in the area of damage.

Question 10

What is electromyography?

Answer 10

Electromyography is a needle study in which the electrical activity of muscle fibers is recorded.
- It can detect damage to muscles and is sensitive to muscle fibers that have been disconnected from their nerves (denervated).

Question 11

What modalities are conveyed by large, myelinated nerve fibers?

Answer 11

Large peripheral nerve fibers convey well-localized touch, pressure, vibration, joint position sense. They also comprise the axons of the alpha motor neurons.

Question 12

What do small-diameter sensory nerve fibers convey?

Answer 12

Small fibers convey pain, temperature, very light touch and make up most of the autonomic nerve fibers as well.

Question 13

What are symptoms of polyneuropathy?

Answer 13

Distal, symmetrical (stocking, glove) sensory loss is most common

• Ankle jerk reflexes are lost early on.
• Some neuropathies are painful.
  
  • Tissue damage if patients cannot detect injury.

Question 14

What are the causes of polyneuropathy?

Answer 14

• Infection (leprosy, HIV, Lyme)
• Diabetes
• Nutritional deficiency (thiamine, pyridoxine, B12)
• Alcohol, toxins (eg, heavy metals), medications/drugs
• Hereditary (eg, Charcot-Marie Tooth)
• Inflammatory (eg, lupus)
• AIDP (Guillain-Barre)
• CIDP

Question 15

What are the potential causes of myopathy?

Answer 15

Muscle diseases (myopathies) may be metabolic, infectious, inflammatory, hereditary, drug or toxin-related.

Question 16

What are the common symptoms of myopathy?

Answer 16

• Proximal and symmetrical weakness (hip and shoulder girdle) before involving more distal muscles.
• There is no sensory loss (though muscles may be tender or cramp).

Question 17

What effect do myopathies have on reflexes?

Answer 17

Reflexes are preserved until very late in myopathy.

Question 18

What additional test would point to myopathy as a cause of weakness?

Answer 18

Many tests may help show muscles are damaged (EMG, muscle enzymes)
- Only biopsy and chromosomal analysis are likely to show the specific etiology.

Question 19

What is the most common neuromuscular/myoneural junction disease?

Answer 19

Myasthenia gravis.

Question 20

Who is most often affected by myasthenia gravis?

Answer 20

Most often young-adult females or late middle-aged males.

Question 21

What are the symptoms of myasthenia gravis?

Answer 21

The symptoms are fatigue of muscles due to damage to acetylcholine receptors by antibody.

Question 22

What blood test may be helpful in diagnosis of myasthenia gravis?

Answer 22

Autoantibodies to acetylcholine receptors are often found.

- These may be idiopathic or due to reaction to thymoma.

Question 23

What regions of the body are most commonly affected by myasthenia gravis?

Answer 23

• Extraocular muscles
• Bulbar myasthenia (swallowing, speech)
• Generalized myasthenia may affect diaphragm and other respiratory muscles causing respiratory insufficiency.

Question 24

What is the treatment for myasthenia gravis?

Answer 24

• Acetylcholinesterase inhibitors will strengthen muscles.
• Immune modulating therapy such as immunosuppressive medication, plasmapheresis or human immune globulin infusion often helps.
• Thymecotomy helps some patients.