Peripheral Neuropathy Flashcards
Why do peripheral neuropathys first manifest distally?
Distal axonopathy is thought to be caused by pathology of the neuronal body resulting in its inability to keep up with the metabolic demands of the axon. This explains why the disease begins in the most distal parts of nerves, and large axons that have the highest metabolic and nutritional demands are more severely affected.
List and discuss the three grades of physical nerve injury, according to “Seddon”
- Neurapraxia
mildest injury type, continuity is preserved. Physiologic block of nerve conduction in the affected axons locally at site of injury.
Key features:
o Transient functional loss i.e. loss of conduction
o Usually due to compression, ischemia, bruising , stretching
o Possibly due to a local ion-induced conduction block at the injury site
o Subtle alterations in myelin structure have also been identified
o Motor fibres are more susceptible - Axonotmesis
Complete interruption of the nerve axon & surrounding myelin sheath occurs.
Perineurium & Epineurium are preserved, axon and myelin degeneration occur distal to the point of injury.
i.e. “anterograde degen”
Key features:
o Nerve conduction distal to the injury site disappears within 24-72 hours post-injury
o The remaining uninjured mesenchymal latticework provides a path for subsequent sprouting axons to re-innervate their target organ
o Full recovery is possible -rate of axonal growth ≈1 mm/d. - Neurotmesis
Partial or Complete severance of the entire nerve occurs.
o Functional loss is instant & complete
o Recovery is blocked by scar formation and the loss of the mesenchymal guide that properly directs axonal regrowth
o Functional recovery without surgical intervention, does not usually occur.
2) List the three (3) main types of degeneration seen when neurons are injured. In each case give a brief definition and description of the key features of each type of degeneration.
a) Axonal degeneration
Primary degeneration of the axon followed by secondary degeneration of the myelin sheath
Key Features:
• Degeneration of the distal axon
• Usually symmetric
• As the disorder progresses, axons typically degenerate from the distal to the proximal end
• Most common pathologic reaction in generalized polyneuropathies
• Often secondary to a metabolic aetiology
b) Segmental demyelination
Focal degeneration of the myelin sheath with sparing of the axon.
Occurs mainly in focal mononeuropathies; also seen in generalized sensorimotor or predominantly motor neuropathies
c) Wallerian degeneration
When the axon degenerates distal to a focal lesion that interrupts its continuity.
Due to:
Trauma
Infarction of peripheral nerve (diabetic mononeuropathy, vasculitis)
Neoplastic infiltration etc
3) List and briefly discuss the types of axonal degeneration.
- Neuronopathic Axonal Degeneration:
The neuronal cell body dies e.g. Motor Neuron Disease - Distal Axonal Neuropathy (=distal axonal neuropathy=dying-back)
the neuronal cell body is under stress, but does not die
Define the term define segmental demyelination.
Segmental Demyelination is the focal degeneration of the myelin sheath with sparing of the axon.
Occurs mainly in focal mononeuropathies; also seen in generalized sensorimotor or predominantly motor neuropathies
Name and discuss the types of segmental demyelination
Primary: Schwann cell is damaged
Secondary: Follows axon degeneration
Can axons regenerate? Discuss
The extent and type of healing that occurs following neuron injury is dictated by the type of injury that caused the damage.
a) Healing following Neuronopathic Axonal Degeneration: Not possible
b) Healing following Distal Axonal Neuropathy: possible once stressor is removed
c) Healing following Wallerian Degeneration: possible (usually requires surgical intervention)
Define the term Mononeuropathy
When a single peripheral nerve is affected
List the most common causes of Mononeuropathy
Vascular Disease • Nerve Compression • Immune • Infectious • Trauma
8) Discuss why the clinical manifestations of Mononeuropathy may vary from case to case.
The specific clinical picture will depend on whether a nerve root, nerve plexus or peripheral nerve has been affected: o Nerve Root Damage Segmental loss of: i) Motor Function ii) Reflexes iii) Sensation Signs usually minimal; symptoms can be severe (pain) Usually only one limb is affected
o Clinical Manifestations of Plexus Damage
o Pain
o Weakness, atrophy: variable (usually more severe than radiculopathy)
o Usually restricted to one limb
o Clinical Manifestations in Single Peripheral Nerve Damage
o Restricted distribution
o Pain, numbness or tingling, atrophy, weakness
9) Write notes on the following mononeuropathies: Carpal Tunnel Syndrome Ulnar Neuropathy Radial Neuropathy Peroneal Palsy
a) Carpal Tunnel Syndrome
o Median Nerve involvement
o Pain in hand, forearm and arm
o Numbness in median distribution
o SSx agg by wrist flexion
b) Ulnar Neuropathy
o Numbness & atrophy of first dorsal interosseous
o Weakness
o Etiology: compression of elbow or Entrapment in cubital tunnel or distal injury
c) Radial Neuropathy
o Weakness of wrist & finger extensors,, brachioradialis
o Etiology: pressure palsy, trauma (humerus F#)
d) Peroneal Palsy
o Causes: Crossing legs, weightloss? Hospitalization, plastercasts, surgery.
o Manifestations:
o Footdrop
o Weakness of foot dorsiflexion and eversion
o Weakness of extensor halluces longus
o Normal inversion and plantar flexion
o Anaethsia: (lower lateral part of leg and dorsum w little-none sensory loss)
o Reflexes are intact
o Wasting ant. Tibial & peroneal muscles
Define the term Mononeuritis Multiplex.
What is the main cause of Mononeuritis Multiplex?
a) Also know as Multiple mononeuropathy or Multifocal mononeuropathy.
o The simultaneous malfunction of >2 different peripheral nerves in separate areas of the body (Source: Merck Manual)
o The individual nerves are usually damaged at different times, but there are >1 damaged nerves at any point in time
Main cause is Vasculitis
11) List two diseases capable of causing Mononeuritis Multiplex
Diabetes, Polyarteritis nodosa, RA
12) Does Mononeuritis Multiplex differ from Peripheral Polyneuropathy?
Discuss
Yes.
MM = >1 peripheral nerve involvement
Polyneuropathy = ALL peripheral nerves affected SYMMETRICALLY
13) List the causes of Peripheral Polyneuropathy.
o Eitiology is used for classification of PP o Inflammatory/Immune o Metabolic (eg diabetes, renal failure) o Toxic (heavy metals, organic solvents, drugs) o Familial (Charcot-Marie-Tooth) o Nutritional (eg thiamine, B12 deficiency)
