10-28 Neuromuscular Diseases Flashcards
“dying back” neuropathy,
“Dying back” refers to a process in which the longest nerve fibers are injured and die.
Wallerian degeneration,
Wallerian degeneration happens to an axon after it has been cut off from its cell body. The distal end of the cut axon degenerates.
epineurium, perineurium, endoneurium,
epi = ct ‘round nerve; peri = ct ‘round fasicules w/in nerve; endo = ct ‘round each axon
lateral femoral cutaneous neuropathy /meralgia paresthetica,
Meralgia paresthetica is entrapment of the lateral femoral cutaneous nerve at the level of the inguinal ligament. Think obese truck drivers
Charcot-Marie Tooth,
Charcot-Marie Tooth is a family of hereditary demyelinating neuropathies that usually begin to show clinical signs in late childhood and adolescence and progress slowly.
—HIGH ARCHES! + hammer toe
—steppage gait (foot drop, weak dorsiflex0
Lambert-Eaton myasthenic syndrome,
Lambert-Eaton myasthenic syndrome is an autoimmune (and often paraneoplastic) condition that produces weakness.
Small vs. Large diameter nerve fibers
- Large peripheral nerve fibers convey well-localized touch, pressure, vibration, joint position sense
- Small fibers convey pain, temperature, very light touch, autonomic
Sensory loss w/ nerve roots vs. periph nerves
b/c of overlap of nerve roots, less sensory loss with nerve root damage than with the periph nn damage
consider learning nerve root weakness location and map distriubtion
from tables in eBook
ID’able causes of periph neuropathy
diabetes mellitus
—nutrition: High EtOH intake (2° to nutritional deficiencies, esp the B vit) In the U.S., the most common single deficiency is in vitamin B12 (2* to poor absorption). Usually myelopathic» polyneuropathy. excesses of pyridoxine (b6) can cause’t
—Toxins such as heavy metals, certain organic solvents and industrial exposures
—Meds, especially some chemo and some drugs used to treat szs or HIV.
—Certain systemic inflammatory conditions such as sSLE, Sjogren’s Syndrome, Wegner’s, and polyarteritis nodosa (most of the time it is in the pattern of mononeuropathy multiplex)
—Chronic infectious 3° syphilis, Lyme and HIV, (the pattern may be a pattern of mononeuropathy multiplex). Leprosy causes a patchy sensory neuropathy.
—metabolic conditions: severe sprue and porphyria.
—monoclonal gammopathy or amyloid.
—immune demyelinating conditions The acute form is termed Guillain-Barre syndrome or AIDP; chronic = CIDP
—familial: Charcot-Marie-Tooth Disease or hereditary motor sensory neuropathy (HMSN)
Polyneuropathy
—presentation
—complications
—causes
a. Distal, symmetrical (stocking, glove) sensory loss, ankle jerk reflexes affected early
b. Some neuropathies are painful
c. May result in tissue damage if patients can’t detect injury
d. Many causes – infection (leprosy, HIV, Lyme), diabetes, nutritional deficiency (thiamine, pyridoxine), ?alcohol, toxins (eg, heavy metals), medications/drugs, hereditary (eg, Charcot-Marie Tooth), inflammatory (eg, lupus), AIDP, CIDP
Myopathies
—Causes
—presentation
—testing
CAUSES: metabolic, infectious, inflammatory, hereditary, drug or toxin-related
PRESENT:
a. Myopathies usually result in proximal and symmetrical weakness (hip and shoulder girdle) before involving more distal muscles
b. Reflexes are preserved until very late in the process
c. There is no sensory loss (though muscles may be tender or cramp)
TESTING: Many tests may help show muscles are damaged (EMG, muscle enzymes) but only
biopsy and chromosomal analysis are likely to show what the etiology is
Myasthenia Gravis —Usually presents in who? —Pathophys —Ab's? —Sx/Present —Tx?
i. Most often young females or old males
ii. Symptoms are fatigue of muscles due to damage to acetylcholine receptors by antibody
iii. Ab’s may be idiopathic or rxn to thymoma
iv. Usually affect eyes, though may be bulbar; Generalized may affect diaphragm and other respiratory muscles causing respiratory insufficiency
TX AChE inhibitors; Immunosuppressives; ?Thymecotomy
Lambert-Eaton Myasthenic Syndrome
—Prevalence
—CAUSE
**uncommon
PRESENT: 1)Weakness of hip girdle muscles with decreased patellar reflexes; 2)Autonomic features
CAUSE: Often with small cell cancer – can be idiopathic; Ab’s against volt-gated Ca++ channels
FYI: Strength increased with sustained contraction (exercise) vs. MG where muscle fatigue w/ use
EMG vs NCS
EMG – evaluates the health of muscles and can detect muscle fibers that have been denervated (either chronically or acutely) and may detect myopathies
NSC — evaluates amplitude and velocity of the fastest, largest nerve fibers
What modalities are conveyed by large, myelinated nerve fibers?
Large peripheral nerve fibers convey well-localized touch, pressure, vibration, joint position sense. They also comprise the axons of the alpha motor neurons.
What do small-diameter sensory nerve fibers convey?
Small fibers convey pain, temperature, very light touch and make up most of the autonomic nerve fibers as well.
Causes of polyneuropathy short list
There are many causes - infection (leprosy, HIV, Lyme), diabetes, nutritional deficiency (thiamine, pyridoxine, B12), alcohol, toxins (eg, heavy metals), medications/drugs, hereditary (eg, Charcot-Marie Tooth), inflammatory (eg, lupus), AIDP (Guillain-Barre), CIDP
myopathy vs. neuropathy
myopathies start proximal and move distally for the most part vs. neuropathies often start distally and move proximally
Effect of myopathies on reflexes
Reflexes are preserved until very late in myopathy.
What additional test would point to myopathy as a cause of weakness?
Many tests may help show muscles are damaged (EMG, muscle enzymes) but only biopsy and chromosomal analysis are likely to show the specific etiology.
Blood test for MG?
Autoantibodies to acetylcholine receptors are often found (although not always). These may be idiopathic or due to reaction to thymoma.
demyelinative neuropathies
CNS: MS; PNS: GBS, CMT
Slowed velocity on NCV
demyelination
fibrillations and PSWs (positive shart waves)
denervation —> think ALS
Tinel’s sign
tapping on nerve of pt leads to shock-like sensation distally
Mees Lines
lines on nails from arsenic poisoning
Congo Red stain shows green apple color
amyloid
GBS as example of AIDP
—sx
transfer to ICU (resp fail/autonomic involvement ∆s HR, BP)
—SX: SYMMETRICAL, ASCENDING, motor & sensory loss; CN’s, resp, & ANS involv.; pain
—Pathogen: ?autoimm (happens w/ infx or injection; responds to immunotx; humor- & cell-med to myelin Ag’s)
—often s/p CAMPYLOBACTER jenjuni infx
—sx onset to clinical presentation = ~1 wks
—Dx w/ EMG, CSF (high prot, w/o pleocytosis)
—TX: plasma xchange, IVIG,
—Mortality = 5%; ANS inv = poor prog
CIDP
—sx onset to clinical presentation = ~1 yr
—tx: corticosteroids ,plasma xchange, IVIG, rituximab
ALS —Presentation generally —Lwr Motoro neuron form s/sx —upper " " " s/sx —EMG —Natural hx
—ASYMMETRICAL
—Lower motoro neuron signs: atrophy, fasiculations, dropped reflexes, weakness, cramping
—Upper motor neuron signs: spasticity, incr/path reflexes, decr RAMS, emotional lability
—EMG: giant MUP (motor unit potentials)
—death 2-3 yrs s/p dx
Myotonic dystrophy
autosomal dominant trinuc repeat in protein kinase ∆ing muscle fiber maturation
—ptosis, myopathic expression
—variable onset; earlier onset = worse prog
Becker’s vs. Duchenne’s Muscular Dystrophy
—Both X-linked
—Both dystrophin gene mutation: Beckers (qualitative); Duchenne (Quantitative)
—Duchenne worse than becker’s: lose mobility/death earlier; cardiac invl, skel deform, contractures all absent in becker’s
—Duchenne has unique signs: Gower’s sign, pseudohypertrophy
Review slides 64-76
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