Denervation

Question 1

What is type grouping and what is it pathognomonic for?

Answer 1

Specific type of lower motor neuron takes over innervation of a given field of fibers; Pathognomonic for reinnervation

Question 2

What is type predominance and what is it frequently evidence for?

Answer 2

Abnormal prominence of one fiber type over the other; Evidence of denervation

Question 3

In this section of frozen biceps muscle, what are the arrows pointing at? What are these indicative of?

Answer 3

Angular atrophic fibers; Highly characteristic of atrophy due to denervation

Question 4

What are the three types of spinal muscular atrophy? What gene is absent in all of these diseases?

Answer 4

Werdnig-Hoffmann Disease (Type I), Intermediate (Type II), Kugelberg-Welander Disease (Type III); Survival Motor Neuron Gene

Question 5

An infant shows progressive and severe weakness and dies within the first year. Histology is shown. What disease did the patient have? What gene is absent?

Answer 5

Werdnig-Hoffman disease (Infantile Spinal Muscular Atrophy); Survival Motor Neuron Gene

Question 6

What are these? What cases are they seen in?

Answer 6

Target fibers; 20% of denervation cases

Question 7

What is going on here? What condition does this resemble? What can cause this? If you stained with NADH-TR would you see target cells?

Answer 7

Type II fiber atrophy; Denervation Myopathy; Corticosteroid administration; No because denervation is not occuring

Question 8

A patient on long term corticosteroids and NMB agents is taken off medication but severe weakness in his muscles persist. What condition does he likely have and what is the mechanism? What is his outcome?

Answer 8

Critical illness myopathy (Myosin heavy chain depletion syndrome); Loss of myosin filaments from muscle fibers; His myosin heavy chains will return and so will his strength.