Peripheral Neuropathy (Week 1--Andersson) Flashcards
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)
Polyneuropathy
Common (2.4%, and 8% over 55 years old)
Multiple nerves, contiguous, typically length dependent (stocking-glove)
Example of motor neuronopathy
ALS
SMA
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
Myelinopathies
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
Chronic
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
