38: Myopathy

Question 1

What do immune checkpoint inhibitors target?

Answer 1

Cytoplasmic T-lymphocyte associated antigen-4 (CTLA-4), programmed cell death receptor-1 (PD-1), programmed cell death ligand-1 (PD-L1)

Question 2

What is myositis provoked by ICPI’s associated with?

Answer 2

Myasthenia gravis

Question 3

What is characteristic of necrotizing autoimmune myopathies?

Answer 3

Necrotic fibers with little to no inflammation on muscle biopsy;
look for statin use, malignancy or connective tissue disease;
HMG-CoA reductase Abs or anti-signal recognition particle (anti-SRP) Ab’s

Question 4

What drugs or toxins can lead to myopathies?

Answer 4

Steroids, EtOH, colchicine, azidothymidine, clofibrate, cholesterol-lowering agents

Question 5

What are the most common metabolic myopathies?

Answer 5

Carnitine palmitoyl-transferase deficiency along the lipid pathway, and myophosphorylase (McArdle’s disease) along the glycogen pathway

Question 6

With lipid pathway disorders, when do you see myopathy symptoms? With glycogen pathway?

Answer 6

After episodes of long or forced exercise;
after brief, intense isometric exercise

Question 7

When does myopathy associated with periodic paralysis tend to manifest?

Answer 7

Fifth or sixth decade with proximal weakness

Question 8

What muscles would ideally be sampled with concern for myopathy?

Answer 8

Most proximal ones, since most myopathies affect the proximal muscles;
look at adult-onset acid maltase deficiency myopathy

Question 9

Why are denervation potentials seen in myopathy disorders?

Answer 9

Thought to be due to segmental inflammation or necrosis of muscle fibers, separating them from a distal, healthy portion of the muscle fiber from the part attached to the endplate

Question 10

Inflammatory myopathies that cause denervation?

Answer 10

Poly/dermatomyositis, IBM, HIV myopathy/polymyositis, HTLV-1 myopathy, sarcoid

Question 11

Dystrophies and other inherited myopathies that cause denervation?

Answer 11

Dystrophin deficiency, FSHD, autosomal recessive distal muscular dystrophy;
Emery-Dreifuss, oculopharyngeal muscular dystrophy, myofibrillar myopathy, limb-girdle 2A

Question 12

Congenital myopathies leading to denervation?

Answer 12

Centronuclear/myotubular and nemaline rod myopathy

Question 13

What infectious myopathies lead to denervating features?

Answer 13

Trichinosis, toxoplasmosis, pyomyositis

Question 14

When can myotonic discharges be seen?

Answer 14

Myotonic dystrophy (type 1 and 2), myotonia congenita, paramyotonia congenita, hyperkalemic periodic paralysis;
Acid maltase deficiency, myotubular myopathy, possibly polymyositis; drug-induced agents like statins or colchicine

Question 15

What activity is seen on EMG for contracture?

Answer 15

Electrical silence

Question 16

What is the most important parameter to measure in myopathy? What does this parameter reflect?

Answer 16

MUAP duration;
the total number of muscle fibers in a motor unit

Question 17

What conditions can lead to SDSA MUAP’s?

Answer 17

NMJ disorders, early reinnervation after severe denervation, periodic paralysis, disorders selectively affecting terminal axons

Question 18

When would reduced recruitment be seen in myopathy?

Answer 18

End-stage muscle disease if all the muscle fibers of a single motor unit are lost, with an actual reduction in the number of motor units

Question 19

What would be seen on SFEMG for myopathy?

Answer 19

Increased jitter and blocking

Question 20

What do approximately 20% of patients with PM and DM have?

Answer 20

Autoimmune or connective tissue disorder (RA, Sjogren, SLE, scleroderma, polyarteritis nodosa)

Question 21

What muscles are commonly involved with PM and DM?

Answer 21

Neck flexors

Question 22

What is the most common inflammatory myopathy in those older than 50?

Answer 22

IBM

Question 23

What muscles does IBM have a predilection for? What bulbar symptom can be present?

Answer 23

Quads and long finger flexors; also biceps, triceps, tib anterior, iliopsoas;
dysphagia

Question 24

IBM MUAP’s fall into what three groups?

Answer 24

1. Small short MUAP’s with polyphasia
2. SDSA and LDLA MUAP’s with polyphasia
3. Normal or LDLA MUAPS with polyphasia

Question 25

What muscle groups does steroid myopathy tend to affect?

Answer 25

Hip girdle muscles

Question 26

Critical illness myopathy shows what being elevated early on? What else is spared? How do most cases come about?

Answer 26

CK;
sensation;
intubated, treated with pharmacologic paralysis and high-dose IV steroids

Question 27

What does NCS show on CIM?

Answer 27

Low CMAP amplitude, prolonged CMAP’s; look for this in 2 or more nerves

Question 28

What does EMG and muscle biopsy show for CIM?

Answer 28

SDSA MUAP’s, denervation potentials, normal/early recruitment;
loss of thick (myosin) filaments on electron microscopy

Question 29

How does Pompe disease come about?

Answer 29

Reduced or absent levels of lysosomal enzyme alpha-glucosidase (GAA)

Question 30

What muscles tend to be affected in Pompe disease?

Answer 30

Paraspinal, abdominal, and respiratory muscles (Pompe for PAR)

Question 31

On U/S, what muscle disorder preserves bone shadow and what obscures it?

Answer 31

Inflammatory myositis tends to maintain the bone shadow; muscular dystrophies tend to obscure the bone shadow

Question 32

What is the muscle most often affected in the LE in FSHD?

Answer 32

Semimembranosus

Question 33

Of the quad muscles, what is relatively spared in IBM?

Answer 33

Rectus femoris