Peripheral Neuropathy (Week 1--Andersson) Flashcards Preview

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Different types of injury to the peripheral nervous system

Root injury: radiculopathy; motor and sensory deficits in segmental distribution

Plexus injury: plexopathy; in the distribution of its organizational anatomy

Peripheral nerve injury in particular nerve distribution can either be neuronopathy (injury to nerve cell body; motor neuron disease for motor, or sensory ganglionopathy for sensory) or peripheral neuropathy (injury to the the peripheral process)



Common (2.4%, and 8% over 55 years old)

Multiple nerves, contiguous, typically length dependent (stocking-glove)


Example of motor neuronopathy




Different types of peripheral nerve injury (peripheral neuropathy)

1) Mononeuropathy: focal; carpal tunnel syndrome, seen in pregnancy with fluid retention

2) Mononeuritis multiplex: focally but multiply; vasculitis

3) Polyneuropathy: diffuse; chronic ethanol toxicity


Three things to consider when diagnosing a peripheral neuropathy

1) Injury to axon or myelin?

2) Is the modality affected motor, sensory or autonomic?

3) Injury to large or small fibers?


Symptoms with motor nerve injury

Loss of function (negative symptoms): wasting, hypotonia, weakness, hyporeflexia, orthopedic deformity

Altered function (positive symptoms): fasciculations, cramps


Symptoms with LARGE sensory nerve injury

Loss of function (negative symptoms): decreased vibration, decreased proprioception, hyporeflexia, sensory ataxia (problem with coordination when eyes closed)

Altered function (positive symptoms): paresthesias


Symptoms with small sensory nerve injury

Loss of function (negative symptoms): decreased pain, decreased temperature

Altered function (positive symptoms): dysthesias, allodynia


Symptoms with autonomic nerve injury

Loss of function (negative symptoms): decreased sweating, hypotension, urinary retention, impotence, vascular color changes

Altered function (positive symptoms): increased sweating, hypertension


Axonal degeneration and reinnervation attempts

Histologically, see denervation atrophy and axon dropout with degeneration and regenerating sprouts for reinnervation

Electrodiagnostically see reduced compound muscle action potential amplitude (CMAP)  with reduced recruitment of muscle fibers on EMG with degeneration and large motor unit potentials on EMG for reinnervation

Clinically see weakness with atrophy with axonal degeneration


Demyelinating neuropathy signs

Histopathologically: loss of myelin and onion bulb formation

Electrodiagnostically: slowed conduction velocity (uniform in hereditary and non-uniform in acquired), EMG reduced recruitment but motor units normal size and amplitude, little or no signs of reinnervation on EMG

Clinically: weakness but NO wasting, tendency for predominant motor over sensory deficits and generalized arreflexia, may have palpably hypertrophic peripheral nerves (greater auricular nerve)


Nerve conduction study to tell if it is axonal degeneration or demyelinating neuropathy

Axonal degeneration = low = fewer "wires"

Demyelinating neuropathy = slow (because demyelination reduces conduction veolcity) and also low


Are the majority of peripheral neuropathies axonopathies or demyelinating neuropathies?

Majority are axonopathies (low)

CMAPs decreased 80% lower limit of normal

Legs more than arms

EMG: signs of devervation (acute, chronic) and reinnervation



Clinically: hypertrophic nerves, arreflexia, weakness w/o wasting, motor more than sensory deficits, NCS can distinguish inherited from acquired

NCS: distal motor latency prolonged (>125% ULN), conduction velocities slowed (<80% LLN), may have conduction block

EMG: reduced recruitment without much denervation


Examples of different causes of peripheral neuropathy (there are many!)

Inherited: Charcot-Marie-Tooth disease (HMSN)

Infectious: leprosy

Inflammatory: Guillain Barre syndrome (acute inflammatory demyelinating polyneuropathy)

Neoplastic: monoclonal gammopathy

Metabolic: diabetes

Drug: vincristine

Toxic: ethanol


How to tell if large or small fibers are affected

Motor fibers are large and myelinated

Autonomic fibers are small and mostly unmyelinated

Sensory fibers can be large (proprioception, vibration and touch) or small (pain and temperature)


6 D's of diagnosing peripheral neuropathy

1) Distribution of deficits

2) Duration

3) What are the deficits (which fibers involved)

4) What is disease pathology (axonal, demyelinating or mixed)

5) Is there a developmental (inherited) neuropathy

6) Is there drug/toxin exposure


1) Distribution

Asymmetry: mononeuropathy, mononeuritis multiplex (vasculitis)

Symmetric (glove/stocking): polyneuropathy


2) Duration

Acute is 4 weeks; subacute is 8 weeks; chronic is >8 weeks

Most polyneuropathies are chronic

Acute polyneuropathies include Guillain Barre, vasculitis

If relapses and remissions, think intermittent toxin exposure


3) Deficits (which fibers affected)

If motor, think Guillain Barre, lead toxicity, Charcot-Marie-Tooth disease

If pure sensory/severe proprioceptive, think carcinoma (paraneoplastic), vitamin B6 toxicity

If autonomic, think diabetes, amyloid, drugs like vincristine, ddI, ddC


4) What is disease pathology

Majority are axonal

If demyelination uniform, then hereditary (Charcot-Marie-Tooth type I)

If chronic sensorimotor axonal polyneuropathy, exclude alcohol, diabetes, hypothyroidism, uremia, B12 deficiency, monoclonal gammopathy (simple blood test and account for majority of neuropathies!)


5) Developmental (inherited) neuropathy

Among most common

Clues: orthopedic deformities, long duration, indolent progression, few "positive" symptoms, examine family members!


6) Drug or toxin exposure

Demyelinating neuropathy could be due to glue sniffing, arsenic

Axonal neuropathy could be due to cancer drugs like vincristine and paclitaxel, antibiotics like chloroquine, ethambutol, isonaizid and metronidazole, or cardiac medications like amiodarone


Ethanol neuropathy

Common axonal neuropathy

Among most common neuropathies worldwide


Numbness, paresthesias, pain in stocking distribution

Sensory more than motor, loss of ankle reflexes


Guillain Barre Syndrome

Common demyelinating polyneuropathy

Rapid, severe, typically ascending paralysis

Post infectious in 60%

Paresthesias, pain, numbness

Symmetric across midline, typically ascending

Autonomic nerves

Reflexes lost

Cytoalbuminologic dissociation in CSF


Diabetic polyneuropathy

Common mixed axonal and demyelinating polyneuropathy

Sensory more than motor

Stocking numbness in all modalities to the ankles; absent ankle reflexes

Autonomic involvement is common

CSF protein frequently elevated

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