Neuromuscular Disorders - Clinical Overview: Peripheral Neuropathy Flashcards
How can you classify neuropathy?
- Motor (weakness)
- Sensory (numbness)
- Small fibre (nerve that carry pain,temperature)
- Motor-neuronpathy (affect anterior horn cells
- Plexopathy (affect the plexus)
What is neuropathy classification based on?
Localisation anatomically
Inherited or acquired
What are inherited diseases broken down into?
- Purely sensory (hereditary sensory neuropathy)
- Purely motor (hereditary motor neuropathy)
- Sensory and motor disease (CMT)
What are the different causes that acquired neuropathy is broken down into?
- Diabetic
- Inflammatory
- Entrapment
- Toxic
What are examples of parts of the nervous system involved in neuropathy?
- Higher centres
- Supplemental motor areas
- Primary motor cortex
- Brainstem
- Spinal cord
- Peripheral nerve
- Neuromuscular junction
- Muscle
What are features of Upper Motor Neuron (UMN)?
- Central symptoms
- Asymmetry
- Increased reflexes
- Increased tone
- Up-going toes
What are features of Motor Unit?
- Autonomic symptoms
- Symmetry
- Reduced reflexes
- Muscle wasting
- Distal numbness
What is the motor unit?
Single anterior horn cells within the cell body of anterior horn of spinal cord
Single motor axon
All of the muscle fibre that single axon applies is the motor unit
What does the number of muscle fibre the motor unit supplies depend on?
Muscle
What can NCS/EMG tell you?
- Neuropathy: presence or absence
- Involvement: sensory, motor or mixed
- Pattern of involvement?
- symmetry
- length dependent
- focal or multifocal
What are the typical features of polyneuropathy?
- Longest nerves most vulnerable (distal and symmetrical)
- Nerves are trophic to muscle (muscle wasting)
- Involved in reflex arc (reduced reflexes)
- Sensory nerves similarly vulnerable (distal sensory loss)
- Confirmatory test to test localisation
What does the median nerve supply?
Abductor pollicis brevis muscle
What is a supramaximal stimulus?
A stimulus that has stimulated all of the axons in that nerve
What is Nerve conduction study (NCS) used to measure?
- How long it takes to get there (distal model latency)
2. How big the response is (amplitude)
What does the amplitude tell you?
The axons are intact and the response is the same throughout
What happens within myelin fibres?
The conduction is really fast
What is the normal conduction in the upper limbs?
50m per second
How long does it take for the message to get from your brain to the muscle along the periphery nerve?
1/50th of a second
What are pain fibres?
Unmyelinated and only conduct at about 3/4 per second
What informs us about the axons?
How big the response is
What informs us about the myelin?
How fast it is conducting
How does Electromyography work?
- Place a needle into the skin in the muscle
- Record while the patient is relaxed to see if there is any spontaneous activity in the muscle [acute problems in the muscle e.g. inflammation]
- Ask the patient to stimulate the nerve e.g. by moving the muscle and record the response
What do you lose in neuropathy?
Some of the axons
What do the remaining axons do?
Cross-sprout and supply the other muscle cells that will otherwise have died [protective mechanism]
What does the nerve cell supply?
200 muscle cells
What suggests a nerve problem?
An increased amplitude of the motor unit
What results in axonal loss?
A reduced amplitude of the whole response
What are symptoms of motor?
- Tripping
- Feet slapping
- Hand weakness
What are signs of motor?
Distal weakness and wasting
What are tests for motor?
Reduced amplitude of NCS, Neurogenic EMG
What are caveats of motor?
Apparent weakness from sensory loss
What are symptoms of sensory (small fibre)?
- Numb feet
- Burns
- Ulcers (neuropathic pain)
What are signs of sensory (small fibre)?
Loss of vibration sensation (and pinprick)
What are tests for sensory (small fibre)?
Reduced amplitudes on sensory NCS (may be normal)
What are caveats for sensory (small fibre)?
Few symptoms in inherited
What are symptoms of autonomic?
- Fainting
2. loss of sweating, impotence
What are signs of autonomic?
Postural BP drop, loss of sweating
What are test for autonomic?
Autonomic function tests
What are examples of acquired neuropathy?
- Acute or sub-acute
- Monophasic or relapsing remitting
- Exposure history
- Asymmetrical
- Adult onset
- Positive sensory symptoms
What are examples of inherited neuropathy?
- Long standing
- Progressive
- Family history
- Symmetrical
- Childhood onset
- Few sensory symptoms
What is Charcot-Marie-Tooth Disease?
- Hereditary Sensory Motor Neuropathy
- Pure motor and pure sensory cousins
- Prevalence 1:2500
- Gradually progressive length dependent weakness and numbness
- Classified according to neurophysiology
- type 1: demyelianting, velocity <38m/s
- type 2: axonal, conduction velocity >38m/s - Dominant, recessive and X-linked forms
How many genes can cause CMT?
60
What are the treatment for CMT hampered by?
Insensitive outcome measures
What are the clinical approach to neuropathy?
- Does the patient have a neuropathy?
- What parts are involved?
- involvement of motor +/- sensory +/- autonomic
- involvement of other organ systems - Is it likely to be inherited or acquired?
- Is it axonal or demyelinating
What is chronic inflammatory demyelinating polyneuropathy?
- Acquired
- Motor and sensory
- Demyelinating
- Proximal and distal weakness of all four limbs with a relapsing and remitting course
- The chronic form of Guillian-Barre syndrome or the peripheral form of multiple sclerosis
- Effective treatment with immunosuppresion
