L12 - Disorders of the motor unit and spinal cord pathways Flashcards
State the two categories of muscle disease? (2)
- Genetic
2. Inflammatory
Describe Myasthenia Gravis?
- Acquired autoimmune disease.
- Antibodies to postsynaptic acetylcholine receptor
- will impair neuromuscular transmission.
Myasthenia Gravis preferentially affects…
Young women (20s and 30s)
Second peak in older men (60s and 70s)
What are some clinical features of Myasthenia Gravis?
- Fatigable muscle weakness.
- Typically worse in day and following exertion.
- Affects eyes, causing fatigable ptosis and diplopia.
- Affects bulbar muscles (dysphagia and dysarthria) and upper limb muscles.
What is Lambert-Eaton myasthenic syndrome?
- Rare, autoimmune syndrome.
- Antibodies against calcium channels of presynaptic motor nerve terminal.
Where does Lambert-Eaton myasthenic syndrome commonly affect?
Lower limbs.
Define muscular dystrophies and give an example?
Inherited disorders characterized by progressive muscle weakness and wasting.
e.g. Duchenne muscular dystrophy
What causes Duchenne muscular dystrophy?
Caused by mutation in the gene coding for the protein dystrophin.
X-linked recessive, affecting males alone.
What is another disease also caused by mutation of dystrophin?
Becker muscular dystrophy.
Less severe.
Describe myotonic dystrophy?
Autosomal dominant.
- demonstrates genetic anticipation
- subsequent generations are increasingly severely affected.
Patients with myotonic dystrophy will usually present in early adulthood with…
- Distal limb weakness
- stiffness
- myotonia (delayed muscle relaxation contraction)
Myotonia
Delayed muscle relaxation following contraction.
What are some other features of myotonic dystrophy?
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Mild cognitive impairment Early prefrontal balding Cataract formation Bilateral ptosis Testicular atrophy Diabetes mellitus Cardiomyopathy with conduction defects Pituitary dysfunction
Briefly describe carpal tunnel syndrome?
Compression of median nerve at wrist.
Give examples of processes that may affect bones or ligaments, thus leading to narrowing of the carpal tunnel…
Pregnancy Obesity Hypothyroidism Acromegaly Rheumatoid arthritis Diabetes Mellitus
What are some symptoms of carpal tunnel syndrome?
- Weakness of thumb abduction.
- Wasting of thenar eminence.
What is Phalen’s sign?
Patient flexes wrist maximally.
Positive test = tingling in thumb, index finger and middle / lateral 1/2 of ring finger.
Used in diagnosis of Carpal Tunnel Syndrome
What is Tinel’s sign?
Performed by light tapping over nerve to elicit sensation of pins and needles.
Positive test = tingling, parasthesia into thumb
Whats the difference between mononeuropathy and mononeuritis multiplex?
Mononeuropathy: disorder of a single peripheral nerve
- usually results from trauma or compression of the nerve
Mononeuritis multiplex: damage to two or more peripheral nerves, painful
- usually results from nerve infarction
Compression of the ulnar nerve at elbow may result in?
Weakness and wasting of intrinsic hand muscles and hypothenar muscles.
- splitting of ring finger sensation
Compression of radial nerve at axilla or mid humerus may reuslt in?
Weakness of wrist and finger extension
Compression of sciatic nerve may result in?
Weakness of knee flexion
Weakness of ankle dorsiflexion, inversion, eversion and plantar flexion.
Compression of common peroneal at the knee may result in?
Weakness of ankle dorsiflexion and ankle eversion.
Compression of the lateral cutaneous nerve of thigh, at the pelvis, may result in?
No weakness!
Purely a sensory nerve.
What is peripheral neuropathy?
‘length dependent nerve damage’
- begins distally and spreads symmetrically. Legs affected before arms.
In peripheral neuropathy why are the legs affected before the arms?
Peripheral nerves are longer in the lower limbs.
What are the common culprits for peripheral neuropathy?
Diabetes Mellitus
Chronic alcohol abuse.
also: vitamin B12 deficiency, renal failure and thyroid disease.
Describe Guillain-Barre syndrome?
Cell mediated autoimmune response is triggered against myelin or other components of the peripheral nerve, causing nerve damage.
What are some key clinical features of Guillain-Barre syndorme?
Usually appears 2-4 weeks after a diarrhoeal or upper resp tract infection.
- weakness in proximal limb muscles.
- facial weakness
Describe cauda equina syndrome?
Compressive lesion located below the end of spinal cord.
- multiple lumbosacral nerve roots are compressed.
- severe lower back pain., leg weakness, numbness over buttocks and perineum and urinary retention.
What is cervical spondylosis?
Degenerative changes of the cervical vertebrae, intervertebral joints and ligaments.
- changes may narrow vertebral canal, causing nerve compression.
What symptoms are often present in cervical spondylosis?
Neck pain, arm pain, tingling and weakness.
How may subacute degeneration of the cord occur?
Vitamin B12 deficiency.
What is syringomyelia?
Presence of fluid-filled cystic cavity within the central canal of the spinal cord.
What is Syringobulbia?
Presence of fluid-filled cyctic cavity within the brainstem.
Recap: Arnold-Chiari malformation
Developmental abnormality in which cerebellar tonsils extend through foramen magnum.
Patients with the Arnold-Chiari formation will often present with?
20-40 y/o
Upper limb pain.
Tingling worsened by coughing.
Loss of pain and temperature sensation (from selective impairment of spinothalamic tracts) in upper limbs may lead to painless burns.
Transverse myelitis
Acute inflammation of the spinal cord.
Paraplegia
Impairment in motor or sensory function of lower extremities.
- does not affect arms
Tetraplegia
Paralysis caused by illness or injury resulting in partial or total loss of use of all four limbs and torso.
Patients with Transverse myelitis may develop?
Paraplegia or Tetraplegia.
Bowel and bladder dysfunction.
Sensory loss below level of lesion.
Which artery provides blood supply to most of the spinal cord?
Anterior spinal artery.
Occlusion in the anterior spinal artery may result in?
‘spinal stroke;
- sudden paraplegia, urinary retention and loss of spinothalamic sensation.
What is foot drop?
Weakness of the dorsiflexion muscles in foot.
Where might you expect a lesion to be that causes spontaneous unilateral foot drop?
Usually has a peripheral cause. Lesion in L5 nerve root Sciatic nerve Common peroneal nerve Deep peroneal nerve Superficial peroneal nerve.
What is the most common cause of spontaneous foot drop?
Peroneal neuropathy, often as a result of compression at neck of fibula at knee level.
- here common peroneal nerve only covered by skin and subcutaneous tissue.
What is Amyotrophic Lateral Sclerosis?
ALS
Rare, neurological diseases that mainly involve nerve cells responsible for controlling voluntary movement.
What occurs in ALS?
UMM & LMM degenerate.
Stop sending messages to muscles.
Muscles unable to function, gradually weaken, start to twitch (fasciculations) and waste away (atrophy).
What is Brown-Sequard syndrome?
Results in weakness, paralysis on one side of body (hemiparaplegia) and loss of sensation on other (hemianesthesia).
What may be a cause of BSS?
- traumatic injury to spine of neck.
- can occur as result of spinal disorders such as cervical spondylosis, arachnoid cyst or epidural hematomas.
What is an epidural hematoma?
When bleeding occurs dura mater and skull.
Describe motor neurons:
- control essential voluntary muscle activity.
UMM - nerve cells in brain
LMM - nerve cells in brainstem and spinal cord.
UMM direct LMM to produce movements such as walking/chewing.
LMM control movement in arms, legs etc.
Spinal motor neurons are also known as…
Anterior horn cells.
Upper motor neurons are also known as…
Corticospinal neurons
Compare and contrast Upper motor neuron lesions to Lower motor neuron lesions:
UMN
- spasticity (increased muscle tone)
- muscle bulk normal
- no fasciculations
- loss of some superficial reflexes such as abdominal or cremasteric.
LMN
- Hypotonia (decreased muscle tone)
- wasting may occur
- fasciculations possibly
- superficial reflexes preserved
