W8 - Peripheral Neuropathy Flashcards
Why do peripheral neuropathies first manifest distally?
The long nerves (supplying the extremities) are the most metabolically active, thus any damage to these nerves is most difficult to repair.
Long sensory nerves affected first and neuropathy will progress in a distal –> proximal, symmetrical “glove and stocking” like distribution. Motor symptoms will occur in this fashion as well.
List and discuss the three grades of physical nerve injury, according to “Seddon”.
According to severity:
Grade I - Neurapraxia
- Axon is complete but has a conduction block.
- Mildest type of nerve injury
- Causes transient functional loss
- Usually caused by compression, ischaemia, brusing or stretching
Grade II - Axonotmesis
- Axonal discontinuity - distal part of axon degenerates (Wallerian degeneration)
- Perineurium and epineurium preserved.
- Myelinated axon degenerates distally to point of injury (“anterograde degeneration”)
- Nerve conduction distal to injury site disappears within 72h post injury
- Remaining uninjured mesenchymal latticework provides a path for supsequent axonal sprouting to innervate target organs.
- Full recovery possible
Grade III - Neurotmesis
- Complete rupture of the nerve (including peri- & epineurium)
- Most severe form of nerve injury
- Functional loss instant
- Recovery blocked by scar formation and loss of mesenchymal guide that properly directs axonal regrowth
- Functional recovery requires surgical intervention
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.
Axonal degeneration:
- Primary degeneration of axon, followed by secondary degeneration of myelin sheath
- Results in degeneration of axon distal to injury site
- As diorder progresses, axons typically degenerate distal -> proximal
- Usually assymetric
- Often secondary to metabolic aetiology
- Most common pathologic reaction in generalised polyneuropthies
Segmental demyelination:
- Focal degeneration of the myelin sheath with sparing of the axon
- Occurs mainly in mononeuropathies, but also seen in generalised sensorimotor or motor neuropthies
- 2 main causes: Acquired (often immune or inflammatory conditions), hereditary (usually Charcot-Marie-Tooth disease)
- Myelin sheath degeneration can be either primary (Schwann cell damage) or secondary (following axonal degeneration)
Wallerian degeneration:
- Occurs after transection to an axon, where the distal portion of the axon degenerates.
- Axon degenerates distal to focal lesion which interrupts axonal continuity
- Neuropathies characterised by Wallerian degeneration include those caused by: trauma, infarction of peripheral nerve (in vasculitis), neoplastic infiltration
List and briefly discuss the types of axonal degeneration
Neuronopathic axonal degeneration:
- Nerve cell body dies
- May be due to metabolic or toxic derangement (eg. MND)
Distal axonal neuropathy:
- Neuronal cell body under stress but does not die
- May be caused by drugs, industrial poisons, metabolic disease, renal failure, deficiency syndromes (malnutrition, alcoholism)
Define the term segmental demyelination and discuss the different types.
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.
Types:
Acquired
- Often caused by immune or inflammatory conditions (eg acute and chronic demyelinative neuropathies, diptheritic neuropathy)
Hereditary - Seen in hereditary polyneuropathies (such as Charcot-Marie-Tooth disease)
Primary - Schwann cell damage
Secondary - Following axonal degeneration
Can axons regenerate? Discuss.
Extent and type of healing that occurs following neuron injury is dictated by the type of injury that caused the damage.
Healing following neuronopathic axonal degeneration (cell body death) – No regeneration possible
Healing following distal axonal neuropathy (injury to axon)
– Regeneration possible once stressor removed (1mm/day).
- Regrowth occurs 24h post-injury
- Must be guided by intact structures (endoneural tubes, nerve fascicles, nerve trunks and undamaged Schwann cells)
Healing following Wallerian degeneration
- Depends on whether endoneural tubes/nerve fascicles and nerve trunks remain intact post-injury
- If so, regeneration will occur 3-4 days post-injury (axonal sprouts develop from remaining distal axon)
– If not, surgical intervention required to stitch up these structures and guide nerve growth towards target organ
Define the term mononeuropathy and list it’s most common causes.
Definition:
Damage to a single peripheral nerve.
Common causes:
- Vascular disease
- Nerve compression
- Trauma
- Immune
- Infections
Discuss why the clinical manifestations of mononeuropathy may vary from case to case.
Clinical manifestations of mononeuropathy will depend on the type/part of nerve which is affected.
If nerve root involvement – segmental loss of motor function, reflexes and sensation, with potential severe unilateral pain. Usually caused by herniated disc.
If nerve plexus involvement – pain, weakness, atrophy more variable, usually restricted to one limb. Brachial plexus can be affected by trauma or neoplasm, lumbosacral plexus by diabetes or neoplasm.
If peripheral nerve affected – restricted distribution of ssx in region of peripheral nerve, with pain/numbness/weakness/atrophy. Usually caused by entrapment or trauma.
Write notes on Carpal Tunnel Syndrome.
- Common mechanism: Compression of the median nerve within the carpal tunnel due to inflammation, flexor retinaculum hypertonicity, tendinopathies of wrist flexors/extensors, carpal bone fractures etc. and usually aggravated by wrist flexion
- Sensory distribution: Paraesthesia and pain in thenar eminence, lateral 3.5 digits
- Motor Ssx: Thenar muscle weakness/atrophy
Write notes on Ulnar neuropathy.
- Common mechanism: Typically caused by compression of ulnar nerve at the elbow, entrapment in tunnel of Guyon or a distal injury
- Sensory distribution: Paraesthesia and pain in the medial 1.5 digits, hypothenar eminence
- Motor Ssx: Weakness and atrophy of 1st dorsal interrosseus.
Write notes on Radial neuropathy
- Common mechanism: Pressure Palsy (“Saturday night palsy”) or trauma (eg. humerus fracture)
- Sensory distribution: Pain and paraesthesia in posterior arm and forearm, dorsal surface of hand and lateral 3.5 digits.
- Motor Ssx: Weakness of wrist and finger extensors and BR.
Write notes on Peroneal Palsy.
- Common mechanism: Crossing legs, weight loss, hospitalisation, plaster casts or surgery
- Sensory distribution: Pain and paraesthesia in lateral aspect of lower leg and dorsum of foot.
- Motor Ssx: Weakness and atrophy of Tib Ant, EHL, EDL. “Foot slap” upon heel strike.
Define the term “Mononeuritis multiplex.” What is it’s main cause?
Definition:
Type of peripheral neuropathy simultaneously affecting two or more non-contiguous (separate areas of the body) nerves. Aka multifocal mononeuropathy.
Main cause:
Vasculitis - which may be caused by a number of conditions (diabetes, polarteritis nodosa, RA)
Common key features:
- Sudden, painful onset
- Typical Ssx: Weakness and paraesthesia, defecits in distribution of several different peripheral nerves
List two (2) diseases capable of causing mononeuritis multiplex.
Any 2 of the following:
- Conditions causing vasculitis (polyarteritis nodosa, rheumatoid arthritis, systemic lupus erythamatosis, Wegeneners granulamatosis, scleroderma)
- Diabetes Mellitus
- Connective tissue diseases
Does mononeuritis multiplex differ from peripheral polyneuropathy? Discuss.
Yes - mononeuritis multiplex affects several non-contiguous peripheral nerves simultaneously, however they are in separate areas of the body.
Peripheral polyneuropathy affects all peripheral nerves and has a symmetrical “glove and stocking” pattern of distribution, and generally progresses distally to proximally.
