#78 - Path of Nerve and muscular disorders.

Question 1

In which type of neuropathy can a biopsy be helpful?

Answer 1

Mononeuropathy multiplex.

NOT distal, symmetrical polyneuropathy.

Question 2

Best place to biopsy a nerve

Answer 2

Sural nerve -
sensory only
small patch on foot
nerve never functions again

Question 3

How to diagnose hereditary peripheral neuropathies (Charcot-Maria-Tooth disease)

Answer 3

physical exam + nerve conduction studies

• Then, genetic testing
• no biopsy.

Question 4

When looking at a muscle biopsy, what are the primary differences between neurogenic and myopathic disorders?

Answer 4

Neurogenic -

• atrophy only
• fiber type regrouping

Myopathic 
-atrophy AND hypertrophy. 
-necrosis
-regeneration
-inflamation
-internally placed nuclei
-fibrosis 
etc.

Question 5

Pneumonic for remembering the characteristics of Type 1 muscle

Answer 5

One mighty slow fat red ox

1 = type 1, m= lots of mitochondria, slow twitch, lipid in them (fat), red meat, ox=oxidative.

Question 6

Differentiate acute denervation vs. chronic denervation on a mm biopsy.

Answer 6

Acute denervation - angulated atrophic fibers in SMALL groups.

Chronic denervation - angulated atrophic fibers in LARGE groups.
as time goes on, motor units get bigger (more cells/neuron), then, with each neuron that dies, bigger groups of cells become atrophic.

Question 7

What are the histologic characteristics of muscular dystrophy?

Answer 7

• myonecrosis
• regeneration
• atrophy/hypertrophy.
• endomysial fibrosis (scarring in the muscle)
• END STAGE: fatty replacement and lots of scarring.

No inflammation - differentiates from myositis.

Question 8

What are the histologic characteristics of myositis? (early and late stage)

Answer 8

• inflammation and necrosis at the early stage
• LATE STAGE
• fibrosis
• regeneration of myocytes.

Question 9

Characteristic pattern of atrophy in dermatomyositis

Answer 9

perifascicular necrosis, inflammation, and MHC class 1 expression..

Question 10

differentiate between dermatomyositis and inclusion body myositis

Answer 10

inclusion body myositis has the same characteristics as dermatomyositis PLUS rimmed vacuoles (collections of lysosomes)

Question 11

Spaces in between muscle cells on a cross section - diagnosis?

Answer 11

Glycogen storage disease - McArdle.

Question 12

You stain for LAMP2 protein (lysosomal protein) in a mm biopsy and it lights up like a christmas tree. Diagnosis?

Answer 12

Pompe disease. (lysosomal abnormality)

Question 13

What do mitochondrial myopathies look like on H&E

Answer 13

Ragged red fibers (proliferation of mitochondria).

Question 14

What do mitochondrial myopathies look like on electron microscopy

Answer 14

Clumps of mitochondria outside cells

-“blocks” of crystallized protein inside mitochondria

Question 15

3 categories of congenital myopathies

Answer 15

1-Thin filament affected - nemaline myopathy

2-Core myopathy - affects Calcium channels

3 - Centronuclear myopathy - endosomal processing affected.

Question 16

nemaline myopathy

histology

Answer 16

blue dots in mm cells (on trichrome and H&E)

Question 17

Centronuclear myopathy histology

Answer 17

nuclei in the middle of the mm cell

Question 18

Core myopathy histology

Answer 18

white space in middle of muscle cells - extruded mitochondria

Question 19

Becker Muscle Dystrophy immunofluorescence

Answer 19

Need to stain against the epitope that is
part of the deleted part of the gene. if you
stain to other parts it will look normal

Question 20

major categories of peripheral nerve vs. skeletal mm pathology

Answer 20

Peripheral Nerve

• demyelination/remyelination
• axonal degeneration

Skeletal mm

• inflammatory myopathy
• muscular dystrophy
• congenital myopathy
• toxic/metabolic myopathy