Basics:
- One axon -> covered by endoneurium
- Multiple axons make up a fascicle which is covered by perineurium
- Multiple fascicles + blood vessels -> covered by epineurium
Classification of peripheral neuropathy:
- Mononeuropathy: single nerve; median N in CTS
- Mononeuritis multiplex: single nerves in multiple locations with asymmetrical pattern (vasculitis)
- Polyneuropathy: multiple nerves contiguous or symmetrical, typically length dependent (meaning they affect longest fibers first) -> “stocking-glove” distribution
- Examples: DM (most common), toxins, HIV, SLE, alcohol, vit B12 def, uremia
| Negative symptoms | Positive symptoms | Examples | ||
| Motor | Weakness, hyporeflexia, wasting, hypotonia, deformity | Fasciculations, cramps | GBS, lead toxicity, Charcot-Marie-Tooth | |
| Sensory | Large fibers | ↓ vibration, proprioception, reflexes, ataxia | Paresthesia | Paraneoplastic, vit B6 toxicity |
| Small fibers | ↓ pain, temperature | Dysesthesias, allodynia | DM, amyloid, drugs (vincristine) | |
| Autonomic | ↓ sweating, BP, urinary retention, impotence, vascular color changes | ↑ sweating, BP | ||
- B6 def or toxicity, cancer, amyloid, HIV, cisplastin\chemo, Sjogren -> affect dorsal root ganglion
- Sensorimotor axonal polyneuropathy: alcohol, DM, hypothyroid, uremia, B12 def, monoclonal gammopathy
- Allodynia: excessive pain as a response to a non-painful ordinary stimulus -> migraine, peripheral neuropathy
- Clues for inherited neuropathy: deformities, long duration, indolent progression, few positive symptoms, family Hx
Axonopathy:
- Axonal degeneration
- On exam: weakness + atrophy
- Length dependent -> legs more than arms
- Example: DM
- NCS: decreased CMAP amplitude
- Worse prognosis, more common
Myelinopathy:
- On exam:
- Weakness, but no atrophy, global arreflexia
- Hypertrophic nerves? Bc of the repeated process of demylination – remyelination (esp peroneal or post auricular N)
- Examples: GBS, CIDP, Charcot-Marie-Tooth
- Charcot-Marie-Tooth is initially a myelinopathy, but they develop secondary axonopathy
- Histopathology:
- Cross section: onion bulb
- Longitudinal: teased fiber
- NCS: decreased conduction velocity, conduction block or temporal dispersion
- EMG: reduced recruitment w\out much denervation
- Better prognosis
Diabetic Peripheral Neuropathy:
- Typical (most common type): distal symmetrical sensorimotor polyneuropathy -> painful
- Atypical: asymmetry or prox more than dist, motor involvement
- Autonomic: gastroparesis, resultants diarrhea, arrhythmia and postural hypotension
- CN: isolated 3rd (pupil sparing) > 4th > 6th
- As soon as they develop neuropathy, it will continue to progress even if you tell the pt to tightly control their blood sugar
Guillian Barre Syndrome (GBS): ‘the peripheral form of MS’
- Acute, motor and sensory (large fiber), length dependent, preceded by illness\infection (most common is campylobacter jejuni)
- Pathogenesis: molecular mimicry
- Clinical:
- Sensory: distal + symmetrical paresthesia, loss of proprioception and vibration, neuro pain
- Motor: distal weakness, areflexia. Resp muscls (diaphragm) weakness is the main issue
- Autonomic: hypo\hyper-tension, arrhythmia, bladder dysnfunx
- Types:
- Acute inflammatory demyelinating polyneuropathy (AIDP) -> most common worldwide
- Other axonal types (AMSAN, AMAN) -> most common in Saudi
- CSF: “albuminocytologic dissociation” high protein (albumin) but normal WBCs? Demyelination in the roots, myelin secretes protein in CSF, not infectious process
- NCS: decreased motor nerve conduction velocity
- Variant: Miller Fisher Syndrome: triad: opthalmoplegia, areflexia, ataxia (anti-GQ1b)
- Treatment:
- ABCs + monitor for resp failure and arrhythmia (cause of death)
- No role for steroids!
- IVIG or plasma exchange (equally effective)
Chronic Inflammatory Demyelinating Polyneuropathy (CIDP): ‘the chronic form of GBS’
- Chronic relapsing sensorimotor polyneuropathy with increased protein in CSF and demyelination
- Course is fluctuating (in contrast w\ GBS)
- Treatment: 1st line -> prednisone
Download the PDF version: here
References:
- Dr Ali Alshehri’s lecture notes
- Toronto notes
- Step up to medicine
