Peripheral neurology Flashcards
What is the peripheral nervous system?
Everything outside of the brain and spinal cord i.e. ganglion, nerve roots, peripheral nerves etc.
What is the function of the peripheral nervous system?
- Sensory input to the CNS
- Motor output to the muscles
- Innervation of the viscera
Where does incoming sensory information enter the spinal cord?
Via the posterior root
Where does motor innervation exit the spinal cord?
The anterior root
Describe the organisation of nerves
Multiple collections of axons in endoneurium in peineurinum in epineurium
What are the nerve fibre types?
- Large myelinated fibres
- Thinly myelinated nerves
- Small unmyelinated nerves
Which nerves are the large fibres and what are the modalities of large fibres?
- Motor nerves
* Proprioception, vibration and light touch
What are the modalities of thinly myelinated fibres?
•Light touch, pain and temperature
Explain what happens at the neuromuscular junction
- Action potential arrives
- Voltage gated calcium channels open and there is a Ca2+ influx
- This causes neurotransmitter vesicles to fuse with the membrane
- ACh is released from the vesicles into the the synaptic cleft where they bind to postsynaptic receptors on the muscle causing ion channels (Na+ and Ca2+) to open
- the influx of Na+ depolarises the cell
- Postsynaptic muscle cell depolarises causing the opening of voltage gated Ca2+ channels causing muscle contraction
What is the clinical presentation of a motor neuropathy?
Weakness/muscle atrophy
What is the clinical presentation of a sensory neuropathy?
- If large myelinated fibres then sensory ataxia, loss of vibration sense +/- numbness and tingling
- If small (thinly myelinated or unmyelinated) then impaired pin prick, temperature, painful burning numbness and tingling
What is the clinical presentation of an autonomic neuropathy?
- Postural hypotension
- Erectile dysfunction
- GI disturbance
- Abnormal sweating
What results in the glove and stocking pattern?
Length dependent axonal neuropathy
What is length dependent axonal neuropathy?
- Diffuse involvement of the peripheral nerves - (myelin and axon degrade?)
- Age >50
- Length dependent so starts in toes/feet
- Symmetrical
- Slowly progressive
- No significiant sensory ataxia
- Any weakness is distal and mild
What are the causes of length dependent axonal neuropathy?
- Diabetes
- Alcohol
- Nutritional - folate, b12, thiamine, B6 deficiency
- Immune mediated - RA, lupus, vasculitis, polyarteritis nodosa
- Metabolic/endocrine - renal failure, hypothyroidism
- Drugs - isoniazid, cisplatin, amiodarone, gold
- Infectious - HIV, Hep B and C
- Inherited - Charcot-marie-tooth, hereditary neuropathy
- Neoplastic - myeloma
- Paraneoplastic - distant cancer
- Critical illness - bed bound for a long time
What is Guillain-Barre syndrome?
- Acute inflammatory demyelinating neuropathy
- Progressive (ascending) weakness over days, flaccid, quadraparesis with areflexia
- May have respiratory/bulbar/autonomic involvement
What is the treatment of Guillain-Barre syndrome?
IV immunoglobulin or aphaeresis (removing blood)
What is the chronic form of Guillain Barre syndrome?
CIDP (chronic inflammatory demyelinating polyneuropathy)
What is CIDP responsive to?
Steroids and IV immunoglobulin
Describe how a nerve conduction study is carried out
- Recording electrodes on thumb and lateral anterior forearm (recording muscle is abductor policies brevis)
- 1st stimulation site on the wrist
- 2nd stimulation site is above the elbow on the anterior aspect of the arm and the 3rd is above that
Describe the results of a nerve conduction study
•Normal - two peaks one shortly followed by a second
•Axonal issue- both peaks are smaller but second peak still follow closely after the first
•Demyelinating issue: 2 presentations:
1. Same height of peak but a conduction delay
2. Conduction block with a smaller second peak, temporal dispersion can occur where the second peak is flattened
What is mononeuritis multiplex?
- Sequential or simultaneous development of neuropathy in 2 or more nerves
- Cluster of conditions, it is not itself a diagnosis
Which sites are most commonly effected in mononeuritis multiplex?
- Common perineal
- Radial
- Axillary
- Median
- sciatic
What are the symptoms of a common perineal neuropathy?
- Weak ankle dorsiflexion
* Sensory disturbance lateral aspect of calf and foot
What are the symptoms of a radial neuropathy?
- Wrist/finger drop
* Sensory disturbance to the dorsum of the hand
What are the symptoms of axillary neuropathy?
- Weakness of shoulder abduction
* “badge” of sensory disturbance inferior deltoid region
What are the symptoms of a median neuropathy?
- weakness of hand muscles: lateral two lumbricals, opponens pollicis, abductor pollicis brevis, flexor pollicis brevis
- Sensory disturbance
What are the symptoms of femoral neuropathy?
- Weak hip flexion and knee extension
* Sensory disturbance of lateral calf and dorsum of foot
What are the common causes of mononeuritis multiplex?
- Diabetes
- Vasculitic - Churg Strauss, polyarteritis nodosa
- Rheumatological - RA, lupus, Sjogren’s syndrome
- Infective - Hep C, HIV
- Sarcoidosis
- Lymphoma
What investigations should you carry out in a suspected mononeuritis multiplex?
- Nerve conduction studies
- EMG
- consider MRI of plexus with contras
- If inflammatory causes, consider an LP
What are the symptoms of muscle disease?
- Proximal limb weakness - difficulty raising arms above head, arising from seated position
- Facial weakness - characteristic myopathic facies, drooling
- Eyes - ptosis, ophthalmoplegia
- Bulbar - dysarthria, dysphagia
- Neck and spine - head drop, scoliosis
- Respiratory - breathlessness (especially on lying flat)
- Myocardial - exercise intolerance, palpitations
What are the causes of muscle disease?
- Muscular dystrophies
- Metabolic muscle disorders
- Mitochondrial disorders
- Myotonic dystrophies
- Inflammatory muscle disorders
- Neuromuscular junction disorders
What is myasthenia Gravis?
- Immune disorder with antibodies against post synaptic acetylcholine receptor
- Fatiguable weakness of ocular, bulbar, neck, respiratory and/or limb muscles
How is myasthenia gravis managed?
- Pyridostigmine (anti-acetylcholine esterase)
* Immunosuppressive therapies - steroids and immunoglobulin
