Neuro Flashcards
What is a motor unit?
comprised of a common anterior horn cell in the spinal cord, its motor axons, nmj, and all muscle fibers that receive innervation from that common anterior horn cell
What are neuromuscular disorders?
= diseases that may affect the anterior horn cell (lmn), peripheral nerve, neuromuscular junction, or muscle
- may cause weakness and atrophy when involving the lmn, motor nerve, nmj or muscle
- sensory disturbances can be present in sensory neuropathies
What is the MRC grading system?
= British Medical Research Council system of grading strength (muscle power)
0: no movement
1: trace movement
2: movement in neutral plane
3: movement against gravity
4: movement against some resistance
5: normal power
What is an EMG?
= needle electromyography, electrodiagnostic test performed to assess motor unit function
- very fine needle is inserted in a given muscle, and it functions as an electrode, capturing electrical signals from the tested muscle
- often preceded by nerve conduction studies (EMG + NCS often named EMG)
What are nerve conduction studies? (NCS)
= delivering mild, brief electrical discharges and capturing electrical signals at a distant spot from the stimulation site
- -> performed to assess several electrophysiologic aspects of large nerve fibers, such as amplitude, latency, duration, and conduction velocity
- may helf dx a neuropathy or radiculopathy
- can be normal in myopathies
What is motor neuron disease?
-commonly refers to Amyotrophic Lateral Sclerosis (ALS), although there are others
-ALS: usually a sporadic disease with progressive degeneration of motor neurons (death of motor neuron cell bodies) of both upper and lower motor neurons
-idiopathic disorder characterized by lower motor neuron involvement (muscle twitching or fasciculations, weakness, limb and tongue atrophy, dysphagia, dysarthria)
-AND upper motor neuron findings (hyperreflexia, increased gag reflex, Babinski sign)
-emotional lability or pseudobulbar affect is sometimes seen
-sensory function is normal
-Tx consists of riluzole and is otherwise mainly supportive
-non-invasive ventilation significantly prolongs survival
(familial forms of ALS are less frequent)
Spinal Muscular Atrophy
SMA, AR disease of the lower motor neurons, causing weakness with normal intellect and no sensory loss
- Werdnig-Hoffmann Syndrome (SMA I) is the prototypical form, which typically presents as “floppy infant” with arreflexia and isolated tongue fasciculations
- may also present in childhood, juvenile and adult forms
- one of the two copies of the Survival Motor Neuron 1 (SMN1) is deleted
- Tx: symptomatic and supportive, prognosis depends on ventilatory status
Kennedy Disease
aka Spinobulbar muscular atrophy
X-linked recessive disease with defects of the androgen receptor and CAG repeat that may cause the anticipation phenomenon
-male patients have muscle cramps, fasciculations, and may develop limb weakness, dysphagia, and dysarthria
-some may develop gynecomastia
-disease is slowly progressive with a normal lifespan***
What is peripheral neuropathy
=disease of motor and/or sensory peripheral nerves
- when the peripheral motor nerve is affected, there are variable degrees of weakness, atrophy, and hypotonia
- when the sensory nerve is involved, there are disturbances of sensation with negative sx and/or positive sx
- may lead to gastrointestinal dysmotility and cardiovascular dysfunction
- brain interprets abnormal sensory input from the nerve damage as numbness, paresthesias or pain
- *presence of numbness does not exclude the presence of pain
What are the common findings in peripheral neuropathy?
- depend on whether there is motor and/or sensory nerve involvement
- reflexes commonly reduced or absent
- usually a distal greater than proximal weakness pattern, atrophy over time
- most follow a distal symmetric pattern, reduced sensation to touch, pinprick, and temp in a length-dependent gradient
- vibration and position sense may be impaired in limbs
- sensory involvement may create long stocking and glove patterns
- shield pattern in chest, sometimes, with less sensation distally
What are the common causes of peripheral neuropathy?
DANG THE RAPIST Diabetes (most common cause in US) Alcohol Nutritional GBS Trauma Hereditary Environmental Toxins Rheumatologic Amyloid Paraneoplastic Infectious Systemic disease Tumor
What is Charcot-Marie-Tooth disease?
aka Hereditary Motor and Sensory Neuropathy
= most common inherited neurological disorder
-sx include distal > proximal weakness, atrophy, and numbness
-commonly AD, though there are AR and X-linked forms
-most common type is caused by disturbances of peripheral myelin leading to uniform demyelination and homogenously reduced conduction velocities of NCS
Distal Symmetric Polyneuropathy
Clinical pattern of peripheral neuropathy
= sensory disturbances in a length-dependent gradient (more deficits distally), symmetrically affecting the limbs
-by the time the neuropathy reaches as far proximal as the knees, there is usually involvement of the fingertips
-may be associated distal limb weakness
-commonly seen in diabetic, alcoholic, and other toxic polyneuropathies
Mononeuropathy
-a clinical pattern of peripheral neuropathy
= motor and/or sensory problems in a single nerve
-classic cases = entrapment neuropathies
Multiple Mononeuropathies
-a common clinical pattern of peripheral neuropathy
= asymmetric pattern of multiple nerve involvement raises the possibility of nerve infarction and/or inflammation
-can be seen with vasculitic neuropathies, such as SLE and polyarteritis nodosa
Autonomic Neuropathies
- a common pattern or peripheral neuropathy
- patients may have postural hypotension, abnormal heart rate variability, gastrointestinal dysmotility, erectile dysfunction, and urinary retention from bladder detrusor muscle dysfunction
- amyloid neuropathy and diabetic neuropathy may present with autonomic dysfunction
Small fiber neuropathy
- a common pattern of peripheral neuropathy
- pt complains of numbness or burning pain, typically in a length-dependent pattern (feet or hands)
- although neuro exam with sensory testing may be abnormal, EMG and NCS are normal (since these only test the large nerve fibers)
- epidermal nerve fiber assessment by skin biopsy may help confirm clinical dx
What is Guillain-Barré syndrome?
= an acquired autoimmune syndrome characterized by ascending weakness of the lower and upper limbs, arreflexia, elevated CSF protein and frequently there is subjective sensation of sensory disturbance without evidence of sensory involvement on physical or electrodiagnostic exam
- may be preceded by infection, trauma, or vaccination
- progression of weakness may lead to quadriplegia and ventilatory dysfunction
- steroids not recommended, treatment options include IVIg and plasma exchange
What is CIDP?
= Chronic Inflammatory Demyelinating Polyradiculoneuropathy
-presents over 2 or more months with proximal and distal motor weakness, elevated CSF protein, and acquired demyelinating features on EMG
Tx = steroids, IVIg, and plasma exchange
What is Parsonage-Turner syndrome
aka brachial plexus neuritis
- characterized by acute onset of arm pain associated with patchy weakness and numbness
- often associated with diabetes mellitus, has been described in association with lupus and vasculitis
- sometimes patients cannot form a circle with forced closing of the tips of the thumb and index finger
What is the role of nerve biopsies?
- may help identify nerve inflammation, demyelination, axonal loss, and deposits
- a common nerve to be biopsied is the sural nerve
What are NMJ disorders?
- affect the electrophysiologic communication between the motor nerve and the muscle membrane
- no sensory involvement in these disorders
What is Myasthenia Gravis?
= an acquired autoimmune postsynaptic neuromuscular junction disorder characterized by fatiguable weakness (worse with prolonged muscle use) of limb, bulbar, and ocular muscles, which may transiently improve with muscle rest
- most commonly there are antibodies against the ACh receptors, or a tyrosine kinase
- commonly develop ptosis, extraocular muscle weakness, difficulty with chewing, swallowing, and proximal greater than distal muscle weakness
How can MG be diagnosed?
patients may present with fatiguable weakness (worse with muscle use)
- antibodies against alpha subunit of ACR
- some have, instead, Ab against muscle specific kinase (MuSK)
- hallmark = decremental response on nerve conduction studies using slow repetitive stimulation
- Single Fiber EMG: may reveal an increased jitter
- injection of a reversible short-acting ACh-inhibitor, edrophonium (Tensilon test) may be diagnostic, showing significant improvement of weakness
- when patients have ptosis, the ice pack test is a useful diagnostic alternative to the Tensilon test
