Muscle Weakness Flashcards
Upper and lower motor neurons diagram
Examples of causes of muscle weakness:
- Upper motor neuron; stroke, tumour etc
- Lower motor neuron; (motor neurone disease, root damage, peripheral neuropathy, single nerve damage)
- Neuromuscular junction; myasthenia
- Muscle fibre; myopathy
- Non-specific; systemic illness
- Functional; poor effort, pain, hysteria, malingering)
Causes of UMN disorders?
Stroke, infection, tumour, degeneration
Where is the likely lesion if weakness is on;
a) one side of body
b) all 4 limbs
c) both legs
d) one limb
a) cerebral hemisphere
b) high cervical spinal cord
c) low cervical spinal cord
d) spinal root or peripheral nerve
Compare the:
a) muscle tone
b) reflexes
c) plantar response
in UMN vs LMN weakness
a) UMN: muscle tone increased (stiffer), LMN: decreased muscle tone (flaccid)
b) UMN: reflexes brisker/exaggerated, LMN: reflexes absent or depressed
c) UMN: plantars upgoing, LMN plantars downgoing
Examples of different groups of LMN disorders:
- Neuromuscular Junction pathology
- Muscle fibre pathology
- Focal Nerve Pathology (single nerve)
- Polyneuropathy (two or more nerves)
- Generalised peripheral neuropathy
- Root Pathology (radiculopathy)
- Motor Neuron Disease (can be UMN and LMN)
Neuropathic lesions can be divided into 2 categories. What are these?
- Axonal loss
- Demyelination
What is the most common neuromuscular junction disorder?
myasthenia gravis
Symptoms of myasthenia gravis / NMJ disorders?
- Proximal weakness
- Fatigability
- Worse as the day goes by
Describe the
a) sensation
b) reflexes
in NMJ disorders. Why?
a) normal
b) normal
are LMN disorders
What test is used to diagnose NMJ disorders?
Repetitive nerve stimulation (RNS)
What is Repetitive nerve stimulation (RNS)?
Electrical stimulation is delivered to a motor nerve repeatedly several times per second. Observing the change in the muscle electrical response (CMAP) after several stimulations, a physician can assess for the presence of an NMJ disease and differentiate between presynaptic and postsynaptic condition
What is the result of RNS in an NMJ disorder?
A decremental response (a smaller and smaller muscle response with each repetitive stimulus) is abnormal and indicates NMJ dysfunction)
What does a decremental response in an RNS indicate?
NMJ disorder
What are 2 major types of muscle fibre pathology?
- Myopathy
- Myositis
What is myositis?
any condition causing inflammation in muscles
What is myopathy?
a disease of the muscle in which the muscle fibers do not function properly, resulting in muscular weakness
Signs and symptoms of muscle fibre pathology?
- Progressive weakness (rapid or slow)
- Usually presents in proximal muscle groups first
- Normal sensation, reflexes, tone
- Moderate wasting
Describe the
a) tone
b) reflexes
c) sensation
in muscle fibre pathlogy?
a) normal
b) normal
c) normal
as is a LMN disorder
What is focal nerve pathology?
Damage to a single nerve e.g. carpal tunnel syndrome
Symptoms of carpal tunnel syndrome?
- Pain in hand and wrist
- Pain occurs when the wrist is bent
- Pain is worse at night
- Aggravation of symptoms happens when the hand is bent forward
- Numbness and tingling sensation in hand especially in the thumb, index middle and ring finger
- Weakness of hands
- A shock-like sensation is felt
What is polyneuropathy?
Polyneuropathy is when multiple peripheral nerves become damaged, which is also commonly called peripheral neuropathy.
What is the msot common cause of polyneuropathy?
Diabetes
What is radiculopathy?
- Radiculopathy describes a range of symptoms produced by the pinching of a nerve root in the spinal column (cervical, thoracic or lumbar).
- Symptoms of radiculopathy vary by location but frequently include pain, weakness, numbness and tingling
What is motor neuron disease?
- Disease of motor neurons (UMN & LMN)
- Progressive motor deficit
- Peak age 50-70
- Can be as young as 20, and much older
Aetiology of motor neuron disease?
- Cells in the CNS and PNS start dying (cellular apoptosis via lysosome digestion)
- Causes:
- Progressive, unknown (idiopathic)
- Sporadic
- 5-10% of cases genetic cause
- Toxins, viruses, trauma, combination
Symptoms and signs of motor neuron disease?
- Painless
- No loss of feeling
- Progressive bulbar palsy: weakness in the tongue, face and palate leading to dysphasia, dysarthria, nasal regurgitation and aspiration
- Normal cognition
Life expectancy after MDN diagnosis?
3-5 years
Functions that are preserved in MDN?
- Eye muscles
- Sphincters
- Sexual activity
There are 2 main forms of electrodiagnostic assessments to assess the function of muscles and nerves. What are these?
- Nerve Conduction Studies (NCS)
- Needle Electromyography (EMG)
What is a Nerve Conduction Study (NCS)?
Uses electrode stickers applied to skin (surface electrodes) to measure speed and strength of signals; sensory and motor assessment
- Sensory assessment;
- During the test, your nerve is stimulated, usually with electrode patches attached to your skin.
- measures how fast an electrical impulse moves through your nerve; can detect nerve damage
- Motor assessment:
- Stimulate motor nerve
- Record amplitude, size, shape of response; recording the compound muscle action potential (CMAP)
- Will give information about how many axons are available
- Gives information about myelination
What is Needle Electromyography (EMG)?
Needle electrode inserted directly into a muscle records the electrical activity in that muscle
What are the 2 earliest manifestations of axonal denervation that can be seen in an EMG?
The presence of positive sharp waves and fibrillation potentials.
What are fibrillation potentials?
spontaneous action potentials generated by recently denervated muscle fibres; often triggered by needle insertion
What are positive sharp waves?
another early manifestation of axonal denervation
What is a motor unit?
a motor unit is the number of muscle fibres supplied by a single motor neuron
What is a motor unit action potential (MUAP)?
EMG –> The representation of the changes generated by a MU is the so called motor unit action potential (MUAP).
