38: Myopathy Flashcards
What do immune checkpoint inhibitors target?
Cytoplasmic T-lymphocyte associated antigen-4 (CTLA-4), programmed cell death receptor-1 (PD-1), programmed cell death ligand-1 (PD-L1)
What is myositis provoked by ICPI’s associated with?
Myasthenia gravis
What is characteristic of necrotizing autoimmune myopathies?
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
What drugs or toxins can lead to myopathies?
Steroids, EtOH, colchicine, azidothymidine, clofibrate, cholesterol-lowering agents
What are the most common metabolic myopathies?
Carnitine palmitoyl-transferase deficiency along the lipid pathway, and myophosphorylase (McArdle’s disease) along the glycogen pathway
With lipid pathway disorders, when do you see myopathy symptoms? With glycogen pathway?
After episodes of long or forced exercise;
after brief, intense isometric exercise
When does myopathy associated with periodic paralysis tend to manifest?
Fifth or sixth decade with proximal weakness
What muscles would ideally be sampled with concern for myopathy?
Most proximal ones, since most myopathies affect the proximal muscles;
look at adult-onset acid maltase deficiency myopathy
Why are denervation potentials seen in myopathy disorders?
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
Inflammatory myopathies that cause denervation?
Poly/dermatomyositis, IBM, HIV myopathy/polymyositis, HTLV-1 myopathy, sarcoid
Dystrophies and other inherited myopathies that cause denervation?
Dystrophin deficiency, FSHD, autosomal recessive distal muscular dystrophy;
Emery-Dreifuss, oculopharyngeal muscular dystrophy, myofibrillar myopathy, limb-girdle 2A
Congenital myopathies leading to denervation?
Centronuclear/myotubular and nemaline rod myopathy
What infectious myopathies lead to denervating features?
Trichinosis, toxoplasmosis, pyomyositis
When can myotonic discharges be seen?
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
What activity is seen on EMG for contracture?
Electrical silence
What is the most important parameter to measure in myopathy? What does this parameter reflect?
MUAP duration;
the total number of muscle fibers in a motor unit
What conditions can lead to SDSA MUAP’s?
NMJ disorders, early reinnervation after severe denervation, periodic paralysis, disorders selectively affecting terminal axons
When would reduced recruitment be seen in myopathy?
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
What would be seen on SFEMG for myopathy?
Increased jitter and blocking
What do approximately 20% of patients with PM and DM have?
Autoimmune or connective tissue disorder (RA, Sjogren, SLE, scleroderma, polyarteritis nodosa)
What muscles are commonly involved with PM and DM?
Neck flexors
What is the most common inflammatory myopathy in those older than 50?
IBM
What muscles does IBM have a predilection for? What bulbar symptom can be present?
Quads and long finger flexors; also biceps, triceps, tib anterior, iliopsoas;
dysphagia
IBM MUAP’s fall into what three groups?
- Small short MUAP’s with polyphasia
- SDSA and LDLA MUAP’s with polyphasia
- Normal or LDLA MUAPS with polyphasia
What muscle groups does steroid myopathy tend to affect?
Hip girdle muscles
Critical illness myopathy shows what being elevated early on? What else is spared? How do most cases come about?
CK;
sensation;
intubated, treated with pharmacologic paralysis and high-dose IV steroids
What does NCS show on CIM?
Low CMAP amplitude, prolonged CMAP’s; look for this in 2 or more nerves
What does EMG and muscle biopsy show for CIM?
SDSA MUAP’s, denervation potentials, normal/early recruitment;
loss of thick (myosin) filaments on electron microscopy
How does Pompe disease come about?
Reduced or absent levels of lysosomal enzyme alpha-glucosidase (GAA)
What muscles tend to be affected in Pompe disease?
Paraspinal, abdominal, and respiratory muscles (Pompe for PAR)
On U/S, what muscle disorder preserves bone shadow and what obscures it?
Inflammatory myositis tends to maintain the bone shadow; muscular dystrophies tend to obscure the bone shadow
What is the muscle most often affected in the LE in FSHD?
Semimembranosus
Of the quad muscles, what is relatively spared in IBM?
Rectus femoris
