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Neuromuscular Diseases Flashcards

1
Q

what is a neuromuscular disease

A

any disease or condition that affects the PERIPHERAL nervous system

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2
Q

what components of the nervous system can be impacted by neuromuscular disease

A

-anterior horn cell (neuronopathy, motor neuron disease)
-dorsal root ganglia (neuronopathy)
-nerve root (radiculopathy)
-nerve plexus (brachial or lumbosacral plexopathy)
-entire nerve (polyneuropathy)
-neuromuscular junction
-muscle

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3
Q

neuronopathy

A

affects the cell body of a motor neuron or a sensory neuron

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4
Q

examples of motor neuron diseases

A

-amyotrophic lateral sclerosis (ALS)
-spinal muscular atrophy (SMA)
-poliomyelitis

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5
Q

amyotrophic lateral sclerosis (ALS) - epidemiology

A

-average age of onset = 60 (can get it at any age though)
-risk factors: older, men, smokers, and history of head/neck trauma
-increasing age is associated with increased risk of developing it
-aka Lou Gehrig’s disease
-most ALS is sporadic, but 2 types are hereditary

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6
Q

amyotrophic lateral sclerosis (ALS) - physical exam signs

A

*lower motor neuron findings (atrophy, fasciculations, weakness, decreased tone)
*upper motor neuron findings (hyperreflexia, increased tone)
*extremity weakness and affects cranial nerves (normal eye movements though)
*NO sensory involvement

NOTE: UMN and LMN findings in the SAME EXTREMITY

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7
Q

amyotrophic lateral sclerosis (ALS) - treatment

A

-riluzole (glutamate inhibitor)
-edaravone (free-radical scavenger)
-phenylbutyrate/taurursodiol
-tofersen (genetic tx for ALS - only for people with SOD1 mutations)

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8
Q

amyotrophic lateral sclerosis (ALS) - prognosis

A

*patients die from respiratory failure an average of 4 years after disease onset

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9
Q

amyotrophic lateral sclerosis (ALS) - pathophysiology

A

central AND peripheral motor neurons die
(amyotrophic = anterior horn cells dying off; lateral sclerosis = lateral corticospinal tracts are become sclerotic/scarred)

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10
Q

amyotrophic lateral sclerosis (ALS) - genes associated with hereditary types of ALS

A

*SOD1 mutation
*C9 mutation (hexanucleotide repeat; most common cause of hereditary ALS)

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11
Q

spinal muscular atrophy (SMA) - etiology

A

*autosomal recessive
*SMN1 (survival motor neuron 1) gene mutation

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12
Q

spinal muscular atrophy (SMA) - types

A

*type I (Werdnig-Hoffman) is most severe and affects infants
*type IV is the most mild (often adult-onset SMA)

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13
Q

spinal muscular atrophy (SMA) - pathophysiology

A

*anterior horn cells die off for unknown reasons (lower motor neuron signs only)
*common cause of hypotonic infants
*most kids die before age 2 without treatment

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14
Q

spinal muscular atrophy (SMA) - treatments

A

*new treatments are extremely effective and kids no longer die from SMA and are “normal”!
-nusinersen (antisense oligonucleotide)
-onasemnogene (gene replacement therapy)
-risdipalm (small molecule)
*more effective when started early

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15
Q

poliovirus - etiology

A

*GI viral infection

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16
Q

poliovirus - pathophysiology

A

*anterior horn cells are killed
*causes focal LOWER MOTOR NEURON dysfunction (weakness and atrophy)
*very rare now, but older patients may still have effects from childhood infection (atrophic leg; post-polio syndrome)

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17
Q

radiculopathy

A

*result from injuries to peripheral nerve roots
*sometimes referred to as a “pinched nerve”
*causes pain, weakness, numbness, and tingling
*typically in the arms or legs

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18
Q

what causes a radiculopathy

A

*most often from mechanical causes (herniated disc, bone spurs)

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19
Q

polyradiculopathies

A

*multiple nerve roots affects
*can be from mechanical causes or pathology in the spinal fluid (infection or cancer)

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20
Q

plexopathy

A

*injury to nerves in either the brachial plexus or the lumbosacral plexus

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21
Q

birth trauma plexopathy

A

*Erb’s palsy (C5/6 and upper trunk plexopathy)
*commonly caused by birth trauma, especially if the shoulder gets stuck during birth (often with mom’s with gestational diabetes because the baby is large)
*“Waiter’s tip hand”

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22
Q

motor cycle accident plexopathy

A

*C8/T1 and lower trunk
*Klumpke’s palsy
*usually causes intrinsic hand muscle weakness

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23
Q

other causes of brachial or lumbosacral plexopathies

A

-metastases
-infection and post-infection
-diabetes

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24
Q

inherited polyneuropathy

A

*Charcot-Marie-Tooth disease
*usually autosomal dominant and demyelinating (but can be any inheritance pattern and can be axonal)
*long-standing neuropathy causes HIGH ARCHES and HAMMER TOES

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25
overview of polyneuropathies
*very common (because of diabetes) *can be categorized: inherited vs. acquired; sensory vs. motor vs. sensorimotor; axonal vs. demyelinating *commonly causes a "stocking-glove" distribution of symptoms (numbness, tingling)
26
how do we determine if a polyneuropathy is axonal vs. demyelinating
*determined by nerve conduction studies & electromyography (EMG) *very rarely by biopsy
27
demyelinating polyneuropathy
*rare *nerve biopsy shows "onion bulbs" *if you see a nerve biopsy on a test, it is probably demyelinating polyneuropathy
28
most common axonal causes of acquired polyneuropathies
***DIABETES** (common, increases risk of amputation) *B12 deficiency *alcohol, toxins, drugs (chemotherapy)
29
acute inflammatory demyelinating polyneuropathy (AIDP or Guillain-Barre syndrome)
***follows GI or respiratory infection (often campylobacter jejuni)** [usually within 4 weeks of inciting onset] *usually **ascending** (starts in feet and works its way up) *can cause complete **paralysis** *patient will be AREFLEXIC EVERYWHERE *treated with IVIG or plasmapheresis (NOT steroids) *cytoalbuminologic dissociation (elevated protein but no WBCs) on lumbar puncture
30
what happens in diseases of the neuromuscular junction
*fluctuating weakness in face and extremities *NO sensory involvement
31
examples of diseases of neuromuscular junction
*myasthenia gravis *Lambert-Eaton myasthenic syndrome *botulism
32
botulinum toxin
*most potent neurotoxin (affects NMJ) *heavy chain binds to pre-synaptic terminal and is internalized *light chain cleaves SNARE proteins (**prevents vesicle from fusing with membrane so Ach cannot be released**)
33
pyridostigmine
***acetylcholinesterase inhibitor *used to treat MYASTHENIA GRAVIS** *more acetylcholine in the cleft allows for more muscle contraction *works in about 30 min and lasts 2-4 hours *excess can cause a cholinergic crisis (DUMBBELSS or SLUDGE)
34
succinylcholine
*depolarizing paralytic drug *action is similar to an acetylcholine agonist (but channel stays open, putting them in a paralytic state) *can cause malignant hyperthermia
35
rocuronium
*non-depolarizing paralytic *competes with acetylcholine for binding to post-synaptic receptors but does NOT open the channels (competitive antagonist of acetylcholine) *reversed by AchE inhibitors (increases Ach to displace the rocuronium)
36
myasthenia gravis - epidemiology
*bimodal distribution: common in young women and older men
37
myasthenia gravis - pathophysiology
*classic **autoimmune** disease - can cross placenta ***production of post-synaptic ACETYLCHOLINE RECEPTOR ANTIBODY** *long-term, the post-synaptic membrane becomes smoother (less complex), causing fewer available acetylcholine receptors, so less ability to cause muscle contraction *the more you do, the worse your symptoms become (**worse towards the end of the day**)
38
acetylcholinesterase inhibitors & myasthenia gravis
*work quickly *do not change the course of the disease *can cause cramps and upset stomach
39
what treatment is used for a myasthenia gravis crisis
IVIG or PLEx
40
thymectomy & myasthenia gravis
*removal of thymus *long course of action *reserved for those with severe disease
41
immune suppressants & myasthenia gravis
*mainstay of treatment *usually prednisone first *other options include azathioprine, mycophenolate, eculizumab, efgartigimod
42
infantile myasthenia gravis
*occurs when mom has myasthenia gravis ***acetylcholine receptor antibodies cross the placenta and affect the fetus** *will go away
43
congenital myasthenia gravis
*extremely rare *different inheritance patterns *caused by DEFECTIVE or MISSING PROTEINS IN THE NMJ
44
Lambert-Eaton Myasthenic Syndrome - etiology
***usually paraneoplastic** (cancer makes the antibodies against the calcium channel of the presynaptic neuron) *can be autoimmune
45
Lambert-Eaton Myasthenic Syndrome - pathophysiology
***antibody against voltage-gated calcium channels of the presynaptic neuron** *presynaptic disease of the NMJ
46
Lambert-Eaton Myasthenic Syndrome - symptoms
*weakness ***weakness may improve with exercise** *typically have dry mouth and areflexia at patella
47
Lambert-Eaton Myasthenic Syndrome - treatments
*treat underlying malignancy *immune suppression/modulation and 3,4 diaminopyridine
48
botulism - etiology
*caused by clostridium botulinum *infantile (grows in intestines); foodborne (ingestion of spores/toxin); wound (black tar heroin)
49
botulism - symptoms
*flaccid paralysis *ptosis *dilated pupils
50
botulism - treatment
*antitoxin *ventilator support *induced vomiting/diarrhea
51
presynaptic vs postsynaptic diseases of the NMJ
***postsynaptic (myasthenia gravis) - the more you do, the worse your symptoms become** (symptoms worse at the end of the day) ***presynaptic - doing more, you generally feel better** (usually symptoms are better at the end of the day)
52
overview of inherited muscle diseases
*most affect children *causes symmetric, proximal weakness without sensory involvement *trouble going up/down stairs, lifting arms above head
53
muscular dystrophies
*result from an **abnormality in the dystrophin complex** (muscle cell membrane protein complex) *a type of inherited muscle disease
54
Duchenne muscular dystrophy - epidemiology
*most common muscular dystrophy in kids ***x-linked recessive (affects boys predominantly)**
55
Duchenne muscular dystrophy - clinical course
*calf psueodohypertrophy & weakness *trouble walking by age 2 *in wheelchair by age 13 *death by age 30 (usually from cardiomyopathy or respiratory failure)
56
Duchenne muscular dystrophy - treatment
*prednisone slows down disease progression (prevents secondary inflammation) *antisense oligonucleotides (used for specific gene mutations) ***GENE THERAPY
57
Duchenne muscular dystrophy - goal of treatment
*switch from Duchenne phenotype to a Becker phenotype *Becker is a less severe form of muscular dystrophy ("relative" absence of dystrophin - much better prognosis)
58
myotonic dystrophy - epidemiology
*most common adult-onset muscular dystrophy
59
myotonic dystrophy - genetic mechanism
*autosomal dominant *trinucleotide repeat (demonstrates genetic anticipation)
60
myotonic dystrophy - symptoms
*causes myotonia (inability to RELAX muscle) *low IQ *cataracts *diabetes *cardiac conduction abnormalities (can lead to sudden cardiac death)
61
glycogen storage disease type 2 (Pompe)
*a type of inherited muscle disease *can be treated with replacement of acid-alpha glucosidase
62
polymyositis
*an acquired inflammatory myopathy **(autoimmune disease that attacks the muscle)** *symmetrical weakness of the proximal muscles of the limbs *muscle biopsy with many WBCs **(CD8+) in the ENDOMYSIUM** *treat with prednisone
63
dermatomyositis
*an acquired inflammatory myopathy **(autoimmune disease that attacks the muscle)** *often **paraneoplastic** (need to look for cancer) *causes HELIOTROPE RASH (purple discoloration over eyelids) & GOTTRON'S PAPULES ***CD4+, PERIMYSIAL INFLAMMATION**
64
inclusion body myositis
*an acquired inflammatory myopathy (autoimmune disease that attacks the muscle) *most common inflammatory myopathy *occurs > age 50, more in men *causes FINGER FLEXION WEAKNESS (unable to flex DIP joints) *very slow progression *often does not respond to treatment
65
blood work testing for neuropathy
*test for common and treatable etiologies of neuropathy: -glucose (fasting of random blood sugar, 2 hour glucose tolerance test, Hgb A1C) -B12 deficiency -TSH -paraproteinemia (SPEP, UPEP)
66
blood work testing for diseases of neuromuscular junction (NMJ)
*myasthenia gravis: -**acetylcholine receptor antibodies** (sensitive and specific for MG; rapid turnaround time) -MuSK (muscle-specific kinase antibody) -about 10% of people with MG are seronegative *Lambert-Eaton: -P/G voltage-gated calcium channel antibodies (takes several weeks to process)
67
blood work for testing for muscle disease (myopathy)
***CK (creatine kinase) level** is the starting point for ALL suspected myopathies additionally: *for muscular dystrophy: genetic testing *for inflammatory myopathy: antibody testing (ANA, DS DNA, myositis panel, etc)
68
2 types of electrodiagnostic (EDX) testing
-nerve conduction studies (NCS) -electromyography (EMG)
69
nerve conduction studies (NCS)
*stimulate a nerve transcutaneously and measure the response from either a different segment of the same nerve (sensory testing) or a distal muscle (motor testing) *the speed of the conduction and amplitude of the response are the key parameters *nerves conduct electricity at about 50 m/s (normal) *demyelinating disease = slow *axonal disease = low amplitude
70
electromyography (EMG) - overview
*a thin needle is inserted into muscle to record the electrical potential of the muscle cells *at rest, muscle should be electrically silent *then, patient is asked to contract the muscle and the voluntary motor units are recorded
71
electromyography (EMG) - abnormalities & findings of disease
*at rest: diseased muscle (from either a primary nerve or muscle etiology) will result in muscle fibers that fire spontaneously *upon contraction: small units = muscle disease; large units = nerve disease and reinnervation
72
testing the neuromuscular junction
1) repetitive stimulation 2) tensilon test 3) ice pack test 4) single fiber EMG
73
repetitive stimulation - myasthenia gravis findings
*slow (3 Hz) stimulation results in a DECREMENT > 10% from baseline *usually a "J-shaped" decrement curve
74
repetitive stimulation - Lambert-Eaton findings
*exercise or fast (50 Hz) stimulation results in an INCREMENT, usually > 200% above baseline
75
repetitive stimulation - botulism findings
*fast (50 Hz) stimulation results in an increment > 200% above baseline
76
tensilon test for testing the NMJ
*Edrophonium, fast-acting acetylcholinesterase inhibitor, is administered and almost immediately, the clinical weakness improves *old-school test for myasthenia gravis
77
ice-pack test for testing the NMJ
cold improves neuromuscular junction transmission (because AchE is less active in the cold)
78
single fiber EMG for testing NMJ
*special type of needle EMG, used to assess and compare the firing rates of 2 muscle fibers in a single motor unit *increased jitter is abnormal
79
peripheral nervous system imaging
*MRI neurography and tractography can depict nerves, but are mainly research techniques *neuromuscular ultrasound can visualize small nerves and subtle muscle changes; now becoming a more common diagnostic test
80
myopathic findings on muscle biopsy
*central nuclei *rounded atrophy
81
neuropathic findings on muscle biopsy
*fiber type grouping *angular atrophy

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