Other Myopathies

Question 1

Myasthenia gravis typically affects females at ages ___.
It typically affects males at ages ___.

Answer 1

Females: 20-30
Males: >50

Question 2

What is the etiology of myasthenia gravis?

Answer 2

Acquired autoimmune disease

Question 3

With myasthenia gravis, patients develop antibodies to ___.

Answer 3

acetylcholine receptors

at the neuromuscular junction

Question 4

myasthenia gravis

What is the result of blocking and subsequent destruction of acetylcholine receptors at the neuromuscular junction?

Answer 4

Decreased surface area and increased gap between nerve ending and muscle

muscle is not inflamed/attacked

Question 5

A 25-year-old female patient presents with acute abnormal muscular fatigability and weakness. You notice that she has ptosis as well.
Which myopathy is likely?

Answer 5

Myasthenia gravis

Question 6

A 58-year-old male patient presents with abnormal muscular fatigability and weakness. You notice that he has diplopia and a mask-like expression with a snarl. In his medical history, it is revealed that he has a thymoma.
What is the likely myopathy?

Answer 6

Myasthenia gravis

Question 7

How are extraocular muscles frequently affected by myasthenia gravis?

Answer 7

• Ptosis
• Diplopia

still have pupillary reflex

Question 8

If a patient has a mask-like facial expression or snarl and you suspect myasthenia gravis, what should you rule out?

Answer 8

Stroke (with MRI/CT)

Question 9

Myasthenia gravis may be comorbid with other autoimmune conditions.
If myasthenia gravis is diagnosed, patient should get a chest CT looking for ___.

Answer 9

Hyperthymus/thymoma

15% of patients have a thymoma

removing thymic tissue can solve myasthenia gravis

Question 10

What are some treatments for myasthenia gravis?

Answer 10

• Thymectomy
• Corticosteroids
• Methotrexate
• Anticholinesterase drugs

improves quality of life

Question 11

When treating myasthenia gravis, plasmapheresis reduces ___.

Answer 11

anti-Ach receptor antibodies

Question 12

What is the likelihood of mortality for myasthenia gravis?
What will likely cause mortality in someone with myasthenia gravis?

Answer 12

Mortality is about 10%, usually due to respiratory insufficiency

diaphragm complications

Question 13

Approximately 15% of patients with myasthenia gravis have a ___.

Answer 13

thymoma

benign tumor, residual thymus

Question 14

What is myositis ossificans?

Answer 14

Metaplasia of soft tissue to bone following trauma/contusion (usually crushing injury)

not inflammatory or autoimmune

Question 15

Myositis ossificans can occur in tendons, ligaments, fat, fascia, joint capsule etc.
Where does it most often occur?

Answer 15

Muscle

Question 16

What are four basic steps describing how myositis ossificans forms bone within muscle after trauma?

Answer 16

1. Fibroblasts infiltrate
2. Fibroblasts become osteocytes
3. Osteocytes make osteoid
4. Osteoid mineralizes into bone within muscle

Question 17

What are the three primary pathogenesis stages of myositis ossificans?

Answer 17

1. Pseudosarcoma
2. Differentiation
3. Maturation

Question 18

In the first 1-2 months, myositis ossificans can look like ___, so an MRI with contrast is more helpful than x-ray.

Answer 18

osteosarcoma

Question 19

myositis ossificans

Pseudosarcoma begins with ___.

Answer 19

trauma

often blunt trauma: crushed or torn

common in football

Question 20

myositis ossificans

After trauma, there is extensive damage and cell death during pseudosarcoma.
Fibroblasts will become osteocytes through metaplasia as a result of ___.

Answer 20

liquefaction

necrosis

Question 21

myositis ossificans: pseudosarcoma

Given that there was trauma, extensive damage, and cell death within the muscle, ___ will appear in the sarcolemma sheath and ___ accumulates as a result.

Answer 21

holes will appear in sarcolemma sheath and fluid accumulates

Question 22

myositis ossificans: pseudosarcoma

Due to cell damage and death, holes appear in sarcolemma sheath and fluid accumulates.
What will happen to make these holes larger?

Answer 22

Phagocytes invade

Question 23

Where in the muscle will there be the greatest damage if a patient is in the pseudosarcoma stage of myositis ossificans?

Answer 23

The center of injury

Question 24

myositis ossificans

During pseudosarcoma, damaged tissue is liquefied and replaced with ___.

Answer 24

sheets of non-specific cells

Question 25

The progression of damage due to myositis ossificans in its pseudosarcoma stage can be aggravated by:

Answer 25

* trauma * massage * stretching * surgery * excess activity * ultrasound

Question 26

# myositis ossificans: pseudosarcoma 15 days post trauma, there is extensive proliferation of ___ tissue.

Answer 26

mesenchymal | minimal osteoid formation at this time

Question 27

Pseudosarcoma can easily be confused with ___ radiographically, but can be differentiated with ___.

Answer 27

confused with **osteosarcoma** radiographically, but can be differentiated with **history of trauma**

Question 28

When does the differentiation stage of myositis ossificans occur?

Answer 28

2-3 months post injury | 8-12 weeks

Question 29

# myositis ossificans During differentiation, mesenchymal cells become ___.

Answer 29

fibroblasts, chondroblasts, and osteoblasts

Question 30

Which cells remove debris during the differentiation stage of myositis ossificans?

Answer 30

Giant cells

Question 31

# myositis ossificans How does the periphery of the injury behave during the differentiation stage? How does the center of the injury behave?

Answer 31

Periphery: begins to mineralize Center: may remain as a fluid filled cyst or filled with undifferentiated cells

Question 32

# myositis ossificans #myositis ossificans What is the zonal phenomenon that occurs during differentiation?

Answer 32

Mature bone develops around periphery due to hematoma This helps rule out osteosarcoma because a neoplastic process develops from the inside out | shows nicely on CT

Question 33

During the maturation stage of myositis ossificans, a ___ is developed that separates the injury from surrounding tissues.

Answer 33

periosteum (mature trabecular and cortical bone) ## Footnote limits contractility/motion/function

Question 34

Once a periosteum has developed during maturation of myositis ossificans, separating the injury from surrounding tissues, what are some ways it may progress/resolve?

Answer 34

* May remain indefinitely * May shrink and disappear (rarely) * May be surgically removed (once matured, too early and it will return)

Question 35

What are some clinical manifestations of myositis ossificans?

Answer 35

* Pain in the muscle * Decreased ROM * Hard palpable lump may be found deep in the muscle * Can be associated with neurological disease (especially with wheelchair)

Question 36

A patient's radiograph of their femur presents a hazy cloud appearance that is hard to differentiate. It may be an osteosarcoma, but it may be myositis ossificans. What are some options moving forward?

Answer 36

* Watch and wait * Get MRI

Question 37

Fibrodysplasia ossificans progressiva is also known as ___.

Answer 37

progressive myositis ossificans

Question 38

How common is progressive myositis ossificans?

Answer 38

Rare | incredibly

Question 39

What is the etiology of progressive myositis ossificans?

Answer 39

Some cases are inherited; no history of trauma

Question 40

Progressive myositis ossificans usually involves which muscles?

Answer 40

Postural muscles: back and major joints

Question 41

With progressive myositis ossificans, muscles become progressively ___ due to ___.

Answer 41

**ossified** (sheet-like) due to **fibroblast metaplasia**

Question 42

Progressive myositis ossificans can present with severe functional disability. When do symptoms begin in life?

Answer 42

Childhood | as early as age 2 or by adolescence

Question 43

Progressive myositis ossificans is generally fatal due to ___.

Answer 43

loss of pulmonary function

Question 44

Denervation affects which muscle fibers?

Answer 44

Both type I and II fibers

Question 45

Denervation includes multiple disease processes that cause progressive muscle ___.

Answer 45

weakness and atrophy | whole nerve compressed

Question 46

What are some examples of traumatic and/or compressive denervation?

Answer 46

* Nerve root avulsion, e.g. due to surgery * Compressive neuropathies. e.g. carpal tunnel, tunnel syndromes

Question 47

Amylotrophic lateral sclerosis (ALS) and spinal muscular atrophies are both examples of ___.

Answer 47

denervation

Question 48

Skeletal muscle fibers are separated from lower motor neurons and the cells have atrophied. They appear angular and dark histologically. What condition is present?

Answer 48

Denervation

Question 49

# denervation What will result if reinnervation does not occur?

Answer 49

Atrophy progresses and muscle fibers are replaced by adipose tissue

Question 50

How do denervated fibers initially distribute? How do they present as the disease progresses?

Answer 50

Initially scattered irregularly, but cluster as disease progresses

Question 51

What is fiber-type grouping as seen in denervation/reinnervation?

Answer 51

As one motor neuron takes over a given field of fibers, fiber types group together Muscle changes fiber type due to motor nerve changing

Question 52

Denervation has caused fiber-type grouping to occur, making one motor neuron take over a field of fibers. What if denervation continues?

Answer 52

Grouped atrophy will occur