Peripheral Neuropathy Flashcards
What are the subcategories in the PNS?
Somatic: Motor/Sensory
Autonomic: Sympathetic/Parasympathetic
What are the differences between the CNS and PNS?
CNS v PNS
CNS contains most somatic cell bodies v. only sensory neurons in dorsal root ganglia and autonomic neurons in ganglia of sympathetic chain
BBB v. Blood nerve barrier (less efficient than BBB)
Oligodendrocytes v. Schwann cells
Mechanical protection by bone (no collagen) v. supported by fibrous collagen
How do the location of the cell bodies of sensory and motor neurons differ?
Sensory: cell body in dorsal root ganglion
Motor: cell body in ventral root (in CNS)
What is the difference in where somatic nerves arise from vs autonomic nerves?
Somatic nerves arrive from cord (except for cranial nerves in brain) while there is a separate system for autonomic nerves in the PNS
What is the difference in the kind of neuron found in dorsal root ganglia v. autonomic ganglia?
Root ganglia: Pseudo-unipolar neuron (cell body in middle of the neuron)
v.
Autonomic ganglia: Mutipolar neuron (cell body at one end of the nerve with the axon going down)
How many pairs of spinal nerves are there and what do they innervate?
31
C1-C8: neck and bits of arms
T1-T12: Trunk and bits of arms
L1-L5: legs
S1-S5 + coccygeal: foot, genitals, perineum
What do nerve trunks contain?
Sensory, motor and autonomic axon before they branch off to their afferent or efferent endings
Describe nerve hierarchy
Axon (in endoneurium)–> fascicle (in perineurium) –> nerve (in epineurium)
What are the endo/peri/epi-neriums made of?
Collagen
What is the difference between motor, sensory, and autonomic neurons?
Basically the same structure but endings are different
TRUE or FALSE?
Axon diameter does not effect whether or not the neuron is myelinated
False
Larger axons are myelinated
Which kind of neuron (myelinated or not) are more critical if damaged?
Myelinated (like ones that control fine movement in the hand)
What is the nerve that is most often biopsied?
The sural nerve
Why is the sural nerve biopsied?
Has no motor function.
Only innervates a small part of the top of the foot
What is the epineurium made of?
Fatty tissue
List the unencapsulated sensory endings in skin and their functions
Peritrichial: senses hair movement
Merkel: Mechanoreceptor that responds to pressure
List the encapsulated sensory endings in skin and their functions
Pacinian corpuscle: vibration, deep touch
End bulb: pressure
Meissner’s corpuscle: light touch, vibration
Ruffini ending: Respond to pressure, skin stretching
Why are not all neurons myelinated?
Myelin is vulnerable to damage and disease
What are the 3 main factors which dictate conduction speed?
Myelin thickness
Axon diameter
Axonal composition
What does the number of axons in the nerve increase?
The amplitude of the axon potential
What are the types of fibers in peripheral nerves?
Myelinated: A (alpha, beta, gamma, omega) and B
Unmyelinated: C
What is the difference between group A and B
A has a diameter of 1-20 micrometers while B is 1-3
The speed of conduction of A is 5-120 m/s while B is 2-15 m/s
A include afferent fibres for proprioception, virbation, touch , pressure, pain, and temperature, somatic efferent fibres
B include visceral fibres; preganglionic visceral efferents
What is the diameter, speed, and function of C group fibers?
Diameter: 0.5-1.5 micrometers
Speed: 0.6-2 m/s
Function: Afferent fibers for pain, temperature; post ganglionic visceral fibres
Which sensory ending group mediates non-specific visceral pain?
C
How can peripheral neuropathy occur?
Axons degenerate die
Myelin can degenerate
Myelin can be attacked
Other parts of the nerve can be damaged
What are the types of injury?
Wallerian degeneration: Physical damaged to the nerve, many forms including crushing, cutting, stretch
Segmental demyelination: Maybe due to damage or disease affecting Schwann cells or directly to myelin
Axonal degeneration: Metabolic damage to axon leading to degeneration
Loss of neuron: Damage where the neuron dies and therefore there is no regeneration
Can peripheral nerves regenerate after damage?
Yes, if the cell body is undamaged the axon can sprout
What guides axon sprouts during nerve regeneration?
Schwann cell basal lamina from the original fibre if intact
What is the rate of regrowth of a nerve following damage?
1-2 mm/day (slow- can take a year to fix a long nerve in leg)
What influences the success of regrowth of nerves?
The underlying cause and severity of the damage
How effective is nerve regeneration?
The inflammation can be repaired
But the remyelination can be less effective
Why is the inflammatory reaction involved in the regeneration of PNS nerves especially interesting?
On the one hand, inflammatory reaction and its mediators in damaged nerve participate significantly in the processes of nerve regeneration . On the other hand, these also develop conditions forneuropathic pain induction .
Name the 5 main types of neuropathies and their presentations
Large fiber neuropathy: Affects hands and legs because longer fibres are more vulnerable
Small fibre neurophathy: Affects lower legs
Proximal motor neuropathy: Affects area above knees
Acute mono neuropathies: Can affect multiple places (e.g. trunk), but is localised
Pressure palsies: Medial nerve (carpal tunnel), ulnar nerve, lateral popliteal
Why are longer nerves more vulnerable?
Nerve itself is more vulnerable to stress due to more metabolic activity (long distance for nerve to have damaged in)
Proteins made in cell body in spinal cord or brain and then they have a longer way to go down
Define peripheral neuropathy
All general disorders of the peripheral motor, sensory, or autonomic nerves, excluding single nerve lesions (mononeuropathies due to entrapment or trauma - carpal tunnel)
What are the kinds or peripheral neuropathy pathologies?
Axonal and demyelinating
What are the causes of peripheral neuropathies?
Hereditary Metabolic Infections Collage vascular disease Deficiency states Toxins Drugs Malignant disease Misc
What is the most common type of neuropathy?
Pressure palsies
What are the hereditary causes of pheripheral neuropathies and what is the most common one?
Most common: Charcot Marie Tooth - aka Hereditaty motor and sensory neuropathy
Hereditary liability to pressure palsies
Familial amyloidosis
Refsum’s disease
What are the metabolic causes of peripheral neuropathies?
Diabetes
Renal failure
Systemic amyloidosis
What are the infectious causes of peripheral neuropathies?
Guillain Barre syndrome and leprosy
What kind of neuropathy does Gillain Barre cause?
inflammatory demyelinating neuropathy
What are the collage vascular disease causes of peripheral neuropathies?
SLE, Systemic vasculitis
What are the deficiency state causes of peripheral neuropathies?
Vitamin B1, B6, B12
Thyamine deficiences
What are the drugs and toxins which cause peripheral neuropathies?
Alcohol, lead, organic solvents
Cytotoxic meds for cancer
What are the malignant diseases that cause peripheral neuropathies?
paraneoplastic syndromes
Multiple myelomas
TRUE or FALSE? CMT disease is only caused by one gene and there is only one kind of CMT
FALSE
There are many types of CMT with different patterns of inheritence and different genes (some affect demyelination others axons)
What is the most common type of Charcot-Marie-Tooth disease?
Type 1A
What are the features of hereditary motor and sensory neuropathy?
Slowly progressive distal muscle weakness and atrophy of hands and feet initially
Symmetrical distal sensory deficit
Foot deformities
Tendon reflexes diminished or absent
Course usually slow and often benign but causes disability
Why does CMT present symmetrically?
Because it is hereditary
What are some foot deformities in CMT?
Pes cavux (high arch) and clawed toes
Why are people with CMT described as having champagne bottle legs?
Their legs look like upside down champagne bottles because of loss of muscle mass in lower leg
How do people get diagnosed with CMT?
Weakness and atrophy (especially in peroneal muscles)
Foot deformities –> gait impairment
Clinical signs of peripheral neuropathy or muscle atrophy found incidentally
Because of hereditary neuropathy family history
TRUE or FALSE?
Patients are usually aware of the severity of sensory loss in CMT
FALSE
How does the electrophysiology of someone with CMT differ from a normal person?
Nerve conduction is slowed (38m/s)
Normal: 50m/s
How are peripheral neuropathies diagnosed?
Sural biopsy or DNA test (for CMT)
How does a fascicular biopsy of a CMT patient differ from a normal one?
Onion bulb appearance: myelin is not compact and poorly formed so multiple layers are unevenly and widely spaced
Why is CMT, a demyelinating disease bad for nerve health?
Lack of myelination in itself might not be as bad but in CMT the demylination leads to axon death –> loss of muscle mass
What is the most common mutation in CMT?
PMP22 - affects schwann cell function
What are the causes of predominantly motor neuropathies?
Inflammatory/Immune: Acute- Guillain Barre, Chronic - Chronic inflammatory demyelinating polyradiucloneuropathy
Acute intermittent porphyria
Diphtheritic neuropathy
Lead neuropathy
Diabetic neuropathy
Inheritied motor and sensory neuropathies - CMT
How does Guillain Barre usually come about and resolve?
Typically follows a viral inflection
Usually is self limiting and recovery can occur but can be fatal if not seen to due to resp muscles
How does CIDP compare to Guillian Barre?
Slower and leads to disability
What are the main types of predominantly sensory neuropathies?
Global sensory loss
Loss of large fibre modalities, ataxic form
Loss of small fibre modalities
What are causes of global sensory loss?
Carcinomatous sensory neuropathy
Diabetes
Most of the metabolic/endocrine neuropathies
Most of the toxic neuropathies
Hereditary sensory neuropathies
What are causes of loss of large fibre modalities?
Idiopathic sensory loss
ganglionpathies
Neuropathy with Sjogren syndrome
cisplatin neuropathy (for cancer)
What are causes of loss of small fibre modalities?
Hereditary sensory neuropathies
Lepromatous neuropathy
Diabetic small fibre neuropathy
Amyloidosis
Fabry disease
Tangier disease
Painful small fibre neuropathy
What are loss of small fibre modalities associated with (symptom-wise)?
Loss of pain and excess pain
What are causes of neuropathies presenting with predominantly autonomic dysfunction?
Diabetes
Amyloidosis
Pandysautonomia
Hereditary dysautonomia (Riley-Day syndrome)
Rare alcoholic neuropathies
How do predominantly autonomic dysfunction neuropathies present?
Postural hypotension - fainting
What are the treatments for neuropathy causes?
Treating the cause:
Inflammatory neuropathies- intravenous immunoglobulins, steroids, plasmapheresis
Vasculitic neuropathy - steroids, immunosupressants
B12 for B12 deficiency
What are some treatments for the symptoms of neuropathies?
Painful neuropathies - membrane stabilisers (amitriptyline, gabapentin, pregabalin
motor problems -Physiotherapy
Orthotics
Why are B12 deficiencies so bad?
They can affect the spinal cord and brain as well
What causes B12 deficiency?
Being a vegetarian or pernicious anaemia
How does vasculitis cause neuropathy?
It leads to nerve ischaemia
TRUE or FALSE?
We don’t diagnose the cause of most severe neuropathies
FALSE
but it is true that we don’t identify the cause of most common neuropathies
