70. Peripheral Nerve

Question 1

List the two different pathophysiologies of polyneuropathy. Which is more common?

Answer 1

1. Axonal PN - 90% of PN - due to axon loss

2. Demyelinating PN - 10% of PN - due to myelin loss

Question 2

How is neuropathy classified? What are the clinical sx of each class?

Answer 2

1. Large Fiber Neuropathy - heavily myelinated
   Sensory - Ab fibers (proprio, fine touch, vibration) sx: numbness, tingling, dead sensation, gait imbalance
   Motor - Aa fibers; sx - weakness
2. Small Fiber Neuropathy - thinly myelinated Ad fibers and unmyelinated C fibers
   sx: somatic - burning, pins/needles, stabbing PAIN; autonomic - dry eyes/mouth, orthostasis, constipation, sweating, sex dysfx
   Length-Dependent (stocking-glove) vs. Non-length dependent (autoimmune disease/cancer)
   normal PE

Question 3

How to Dx evaluate neuropathy? how to differentiate axonal v. demyelinating PN?

Answer 3

EMG: differentiator (axonal PN = less amplitude response; demyelinating = more delayed response) for large fiber neuropathy ONLY
Small Nerve Fiber Testing: skin biopsy (count nerve fibers) or sweat testing (autonomic dysfx)

Serologic: Consider DM, Vit B12, B6, B1; EtOH, CMP for renal disease, Heavy Metal Poisoning, Infectious etiology, Meds

Question 4

Tx for Axonal PN

Answer 4

tx underlying cause
Pain mgmt - antiepileptic, antidepressants, analgesics, vit supplements
PT for gait/balance

Question 5

Cause for Demyelinating PN (list etiologies, special disease focus)

Answer 5

Autoimmune: Guillan Barre Syndrome
- most common cause of acute generalized weakness
- CP: ascending paresis with sensory changes
- CSF: albuminocytologic dissociation (high albumin, low cells)
- immune attack destroys myelin sheathing (preceding illness/vaccination/surgery)
- tx: plasma exchange, IVIG (NO STEROIDS)
Hereditary Disease (Charcot Marie Tooth), Infectious (LYME, Diptheria), Toxic (amiodarone, glue sniffing, anti-TNFalpha)