PERIPHERAL neuropathies Flashcards
what are the different mechanisms of damage for peripheral nerves?
- demyelination
- axonal degeneration
- compression
- infarction
- infiltration
how does demyelination occur, what is the neurophysiological consequence and typical aetiology
schwann cell damage leads to myelin sheath disruption. Causes marked slowing of conduction. Eg: G-Bs and many genetic neuropathies.
how does axonal degeneration occur, what is the neurophysiological consequence and typical aetiology
axonal damage causes nearve dying back from the periphery.
Conduction velocity initially normal.
Tpically in toxic neuropathies,
longest axons are affected first.
how does compression occur, what is the neurophysiological consequence and typical aetiology
focal demyelination at the point of compression cuases disruption of conduction,
eg. Entrapment.
how does infarction of nerves occur, what is the neurophysiological consequence and typical a
microinfarction of cvasa nervosum
in diabetes,
arteritis,
poyarteritis nodosa,
Churg-Strauss syndrome.
what is the pathology and aetiologies in neuronal infiltra
infiltration by inflammatory cells in leprosy and granulomas (sarcoid) and neoplasms.
Clinical clues for pathogenesis of AXONAL polyneuropathy:
●Musclle wasting
●Pain
● Sensory Sx prominent
●only ankle reflexes lost
neurophysiology of AXONAL polyneuropathy
●small amplitude
●normal velocity
●normal F waves
●needle EMG - denervation
clinical clues for DEMYELINATING polyneuropathy
●weakness without much wasting
●mainly motor Sx
●generalised loss of reflexes
neurophysiology for demyelinating polyneuropathy
●prolonged distal latency ● slow velocity ●conduction block ●prolonged F waves ●needle EMG may be normal
Axonal neuropathies aetiologies
•Acquired
–Diabetes / pre-diabetes
•distal symmetrical sensory (length dependent)
•diabetic proximal neuropathy (lumbosacral radiculo-plexus neuropathy)
•mononeuropathies (III, VI, truncal root)
–Vitamin B12 or folate deficiency, hypothyroidism
–Drugs & Toxins
•Alcohol
•Chemotherapy
–Mononeuritis multiplex
•Vasculitis or inflammatory
–Idiopathic
•Hereditary
–Charcot-Marie-Tooth disease, etc
AETIOLOGIES OF demyelinating neuropathies
•Acquired –Acute: Guillain-Barré Syndrome –Chronic: •CIDP (chronic inflammatory demyelinating polyradiculoneuropathy) •IgM paraprotein-associated
•Hereditary
–Charcot-Marie-Tooth disease
if the polyneuropathy is symmetrical, what is the likely type of aetiology?
In general, toxic & metabolic nerve disroders produce symmetrical syndrome.
what aetiologies if it’s predomantly MOTOR neuropathy?
GBS
porphyria
malignancy
lead poisoning
B1 (thiamine) deficiency neuropathy Sx
burning dysthesias feet >hand, wasting of distal>proximal muscles, axonal neuropathy.
