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Pathology of the Peripheral Nervous System

What presents with acute ascending paralysis bilaterally, starting in the feet?
GBS

What infectious agent do you suspect if your pt presents with bilateral facial neuropathy?
Borrelia burgdorferi

What's a common incorrect treatment for trigeminal neuralgia?
dentists pull teeth unnecessarily


Which three cranial nerves account for the majority of mononeuropathies in clinical practice?
facial (VII), trigeminal (V), and oculomotor (III)

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What is the most common cranial nerve neuropathy?
Bell's palsy
25/100,000 people

What is the most common presentation of Bell's palsy?
unilateral facial weakness
that began abruptly
often preceded by pain behind the ear
possible hx of URI 1-3 weeks prior
can be bilateral
must protect eyes that won't close

What are some possible etiologies of Bells?
autoimmune?
viral infection of facial nerve
HSV-1 implicated because its DNA found in nerve bx speciments
allo tx: anti-hsv regimen and prednisone

When might you expect a worse prognosis with Bell's palsy?
older patients
hyperacusis
altered taste sense

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What's the diagnosis if the pt experiences short periods of intense, paroxysmal pain in the maxillary or mandibular area of the face?
trigeminal neuralgia

What's the old name for trigeminal neuralgia?
tic douloureux

What's the most common cause of trigeminal neuralgia?
most common: idiopathic
many cases also caused by BV compression of trigeminal nerve root at the pons
can be caused by hyperactivity of the trigeminal nerve nucleus

What's the treatment if the nerve irritation is caused by contact with an artery or vein?
surgery to anchor the blood vessel away from the nerve

Which artery is usually involved if the nerve root is compressed at the pons?
SCA = superior cerebellar artery

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What are some common mononeuropathies of limb nerves? (5 in my list)
carpal tunnel syndrome
ulnar neuropathy
brachial plexus n.
peroneal n.
meralgia paresthetica
plus one not in a limb: perineal paresthesia also common

What are some risk factors for carpal tunnel?
obesity
pregnancy
hypothyroid
depleted B6
repetitive motion: carpenters, typists, kayakers

What nerve is compressed in carpal tunnel?
radial

What are some treatments for carpal tunnel?
B complex vits esp B1, 6, 12 for nerve health
splint to sleep or work (minimize repetitive motion or resting at end of ROM)
anti-inflammatories
job change

What nerve is involved in meralgia paresthetica?
lateral cutaneous
-->sensory loss, prickling, or hypersensitivity on anterolateral thigh
boundaries sharply defined, no abn in motor or DTR's

Who is most likely to get meralgia paresthetica?
an obese person dt incr mechanical stress on inguinal ligament
tx: wt loss, steroids, nerve ablation last

What does LFCN stand for?
lateral femoral cutaneous nerve

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Which patients most often have polyneuropathies?
diabetics
symmetrical, distal, sensorimotor
sensory loss in feet and fingers, mild weakness of feet and ankles is typical

Besides the glove and stocking distribution numbness, what sensation may be especially difficult in this?
burning
wants to put feet in bucket of ice water

What's the pathogenesis of diabetic polyneuropathy?
in this class we are told it is due to:
microvascular dz, endothelial inflam, atherosclerosis-->hypoxia-->ischemia of nerves
another proposed mechanism is the accumulation of sorbitol and depletion of inositol in nerves

What does the decreased inositol supposedly cause?
reduced activity of the sodium potassium pump-->changed conduction, structural alterations of axons

In diabetic rats, a reduction in nerve blood flow and oxygen tension causes what?
abnormal nerve conduction
partial correction of abnormalities can be achieved with 100% O2

Diabetics with peripheral neuropathies also may have autonomic changes. How do these express?
orthostatic hypotension
impaired gastrointestinal motility (gastroparesis sometimes)(celiac plexus neuropathy)
blunting of sympathetically mediated warning symptoms of hypoglycemia

this is interesting

So the reason why diabetics often do not recognize their own hypoglycemia is that their autonomic nervous system has been damaged by long duration high blood sugar, by whichever mechanism you like.

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What part of the nervous system degenerates in 60% of patients with longterm renal failure?
distal axons

What is the mechanism?
not known for certain
called uremic neuropathy, suspect that neurotoxic uremic buildup injures nerves
even severe cases can resolve in months with tx (dialysis, transplantation)

====

What is the most common cause of acute generalized paralysis in the US?
Guillain-Barre syndrome (GBS)

What caused the last major outbreak of GBS?
the swine flu vaccine of 1976
maybe
suspicion of AI rxn, many pts report a URI prior

How challenging is the diagnosis of GBS?
early: quite
dx after sx are full blown is not difficult

What's the first symptom of GBS?
first sx is prickling paresthesia, beginning in feed and spreading up legs
often pts are discharged from the ER with dx of anxiety
return a day or two later with obvious progressive limb weakness

====

What is CIDP?
chronic inflammatory demyelinating polyradiculoneuropathy

What causes it?
auto-immune

How common is it?
rare

How does it present?
like GBS but slower: insidious, weeks to months

What is the course of the dz?
paralysis may relapse and remit or be persistent
some experience gradual spontaneous remission
may interfere with breathing (Miller sez dt paralysis of intercostals!!?)

====

How do you diagnose amyloid neuropathy?
nerve biopsy
sx: symmetrical sensory and motor polyneuropathy

What are the two types of amyloid neuropathy?
"systemic" and "familial"
he says you can tell acquired from inherited by staining for immunoglobulins
HUH? so acquired is autoimmune?

====

Can cancer cause neuropathies?
but of course
seems to be dt immune response to cancer accidentally demyelinating nerves

====

What is the mechanism of ethanol-related neuropathy?
don't know
mb dt neurotoxic effect of ethanol
or malnutrition (thiamine and other B vits depleted)
and seems to me also blood sugar issues
attempts to produce ethanol neuropathy in well fed animals have failed
in cell cultures nerve cells don't grow with moderately high concentrations of ethanol

What's the first symptom of ethanol neuropathy?
loss of distal DTRs

What are the main symptoms?
burning or stabbing pain in feet and sometimes hands
maybe also decreased sensation, or hypersensitivity
mild distal weakness
(sounds just like diabetic sx)
"painful foot syndrome"

What other signs and symptoms are usually present if a pt has this neuropathy?
chronic liver disease
memory impairment
gait ataxia: wide gait dt posterior column compromise

What do the Danish put in their beer to prevent all this?
thiamine and pyridoxine (vitamins B1 and B6)

====

What are a couple types of drugs that can cause neuropathies?
chemotherapy
tuberculosis tx (needs B complex)
drugs containing gold or platinum

What do you call it when the sx get worse even after you've stopped taking the troublesome drug?
coasting

What's another metal that causes neuropathies (besides gold and platinum)?
lead, arsenic, mercury

What are the sx of lead neuropathy?
mainly motor
predilection for upper limbs
also assoc with abdominal pain, constipation and anemia

Which metal causes abdominal pain, vomiting, diarrhea, skin and nail changes?
arsenic

====

What anaerobic bacterium can cause paralytic illness?
Clostridium botulinum

How does C. botulinum affect the PNS?
blocks voluntary motor and autonomic chlinergic neuromuscular junctions
prevents motor fiber stimulation

What environment makes C.bot happy enough to grow and make poison?
low salt
low acid
no oxygen

What nerves are affected first?
cranial nerves-->diplopia, ptosis, dysarthria, then can't hold head up
followed by more cranial nerve palsies-->descending flaccid paralysis
may involve respiratory muscles

What happens to the sensory pathways?
nothing, they're fine

What are some other infectious agents that can cause polyneuropathies? (4)
leprosy
HIV/AIDS
lyme dz
varicella zoster

What's the name of the bug that causes leprosy?
Mycobacterium leprae

What climates support leprosy growth?
tropical and subtropical

What do you culture the bacterium in for diagnosis?
armadillo footpads
seriously now folks

What causes the sensory neuropathy (distal burning sensation) in HIV/AIDs?
the meds?
vitamin B deficiency?
not always known

What spirochete infection is transmitted to humans get when bitten by Ixoides ticks?
Borrelia burgdorferi

What are the main early neurologic features of Lyme disease?
cranial neuropathies and/or spinal nerve radiculopathies
headache and stiff neck may indicate meningeal inflam
often misdx'd as Bell's palsy

Between the cranial neuropathies and the spinal radiculopathies, which has a better prognosis?
the cranial neuropthies usually resolve, but the peripheral neuropathy of late stage dz may become chronic

What is the most common viral pathogen affecting the PNS?
varicalla zoster virus (VZV)

What viral family does VZV belong to?
herpes

What is a person's initial infection with VZV known as?
chicken pox

When the virus proliferates later in life due to immune system decline, what is it?
shingles

What causes the patient to feel bad long before the skin symptoms arrive in shingles?
interferon

What's the usual presentation of shingles?
first pain in dermatomal pattern
followed in 3-14 days by exquisite pain and vesicular rash
1-3 dermatomes involved
rash lasts 7-10 days
sensory changes may last much longer, be permanent

What do you call it when the pain continues 1-2 months (or more) after the rash is gone?
PHN = post herpetic neuralgia

What population has the highest risk of PHN?
old folks
incidence is 45% in pts over 65 yo

What do you call it when the virus infects the facial nerve near the inner ear?
Ramsay Hunt syndrome
may have vesicles on nose or in ear canal
concern that optic nerve could be involved-->blindness

What two nerve distributions are most commonly affected by shingles?
thoracic and trigeminal

Which trigeminal branch most often is affected by shingles?
opthalmic branch

What tx does Miller favor for PHN?
acupuncture

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