Neuromuscular Flashcards
Upper Motor Neurons
Cerebral cortex → ventral motor horn
Direct, influence, & modify reflex arcs
Form synapses w/ interneurons & lower motor neurons before projecting to periphery
Corticospinal Tract
Motor transmission
Receives information from sensory cortex
AP to 1° motor neuron
Synapses w/ 2° efferent motor neuron
Decussates at medulla & travels down the spinal cord via the anterolateral tract
2° motor nerve synapses w/ 3° efferent motor neuron at ventral horn
3° (lower motor neuron) projects down to the skeletal muscle
Corticobulbar Tract
Cranial nerves
Bilaterally III, IV, VI, IX, X, XI
Unilateral facial VII & hypoglossal XII
Involved in precise motor movements
Lower Motor Neurons
Neurons located in brain stem & spinal cord
Direct influence on muscles
Send axons into PNS to synapse one & control skeletal muscle cells
Lower motor neurons that pass through the spinal nerves 1° control limb & trunk muscles
Pass through cranial nerves 1° control the head & neck skeletal muscles
NMJ
Neuromuscular junction
AP initiates synaptic transmission
Na+ channels depolarize the axon terminal membrane
Depolarization causes VGCa2+ channels to open
ACh diffuses across the synaptic cleft & binds to receptors on postsynaptic membrane
Depolarizes post-synaptic AP
ACh uptake to resynthesize/recycle
Upper Motor Lesions
Motor cortex Muscle groups are affected Mild weakness Minimal diffuse muscle atrophy No fasciculations ↑muscle stretch reflex Hypertonia & spasticity Pathological reflexes
Lower Motor Lesions
Ventral horn (spinal cord) & motor nuclei (brainstem) Individual muscles affected Mild weakness Severe muscle atrophy Fasciculations ↓muscle stretch reflex Hypotonia & flaccidity - Babinski sign
Upper Motor Neuron Disorders
Cerebral palsy Multiple sclerosis CVA Parkinson's Huntington's
Cerebral Palsy
Non-progressive disorder caused by injury or abnormal development in the immature brain
Before, during, or after birth up to 1yo
Damage or defects in the corticospinal pathway
CP S/S
Muscle weakness Loss fine motor control Impaired speech Drooling Exaggerated deep tendon reflexes Spasticity Extremity rigidity Scoliosis, contractures, joint dislocation
Vision or hearing impairment Swallowing problems Seizures Intellectual disability Reflux disease
CP Treatment
No cure ↑ADLs Surgery (ortho, dental, general, ophthalmology, ENT) - Dorsal rhizotomy - Antireflux operation - Intrathecal baclofen pump Botulinum toxin PT/OT
CP Anesthetic Considerations
Hold preop sedative Caution w/ opioids Difficult vascular access Airway concerns d/t dentition, secretions, TMJ, ankylosis, & contractures Potential RSI Succinylcholine does not ↑K+ release Cautious NDMR admin ↓MAC 20-30% Prone to bleeding, hypothermia, & intravascular depletion Slow emergence
Multiple Sclerosis
Autoimmune disease characterized by combination demyelination, inflammation, & CNS axonal damage
Peripheral nerves not affected
MS S/S
Parethesias (face, arms, fingers, legs) Muscle weakness/fatigue Painful muscle spasms Visual problems (optic neuritis & diplopia) Autonomic instability Bulbar muscle dysfunction Cognitive dysfunction (advanced MS)
MS Treatment
↓spasticity, tremors, bladder spasms Diazepam Dantrolene Baclofen Glucocorticoids Immunosuppressants CD20 monoclonal antibody - interferon B1a of glatiramer acetate
S/S exacerbated by stress, ↑body temp, infection, hyponatremia
MS Anesthetic Considerations
AVOID SUCCINYLCHOLINE Caution w/ NDMR admin Avoid surgery during flare Avoid spinal block Epidurals safe Aspiration risk ↑risk DVT Stress-dose steroids Exaggerated hypotensive effects
Cerebrovascular Accident
Stroke characterized by sudden neurologic deficits resulting from ischemia 88% or hemorrhage 12%
CVA S/S
Anterior cerebral artery - contralateral leg weakness
Middle cerebral artery - contralateral hemiparesis & sensory deficit (face/arms > legs), aphasia, contralateral visual field defect
Posterior cerebral artery - contralateral visual field defect & hemiparesis
Penetrating arteries - contralateral hemiparesis & contralateral hemisensory deficits
Basilar artery - oculomotor deficits and/or ataxia & crossed sensory & motor deficits
Vertebral artery - lower cranial nerve deficits & ataxia w/ crossed sensory deficits
CVA Treatment
Aspirin
TXA (IV admin or VIR direct infusion)
Surgery (crani/cerebellar resection)
CVA Anesthetic Considerations
Aspiration & DVT risk
Maintain blood glucose
Blood pressure maintenance
Parkinson’s Disease
Neurodegenerative disorder
Unknown cause
Loss dopaminergic fibers in the basal ganglia
Regional dopamine concentrations are also depleted
Results in diminished neuron inhibition controlling the extrapyramidal motor system & unopposed ACh stimulation
Parkinson’s S/S
Skeletal muscle rigidity (pill-rolling) - more prominent during rest & disappears during voluntary movement
Rigidity
Akinesia - loss voluntary movement
Diaphragmatic spasms
Dementia
Depression
Facial immobility (infrequent blinking & paucity emotional expressions)
Parkinson’s Treatment
Levidopa - dopamine precursor Carbidopa - peripheral dopa decarboxylase inhibitor Amantadine Selegline & Rasgiline Rpinirole - dopamine agonist Entacapone - COMT inhibitor Donepezil & Taurine - AChEi Amatadine - antiviral
Parkinson’s Anesthetic Considerations
Continue Levidopa therapy Aspiration/airway risk Hypertension Post-extubation laryngospasm Avoid benzodiazepines Ideal volatile agent = Sevoflurane NDMB less effective Use Sugammadex Avoid indirect-acting NT releaser (Ephedrine) Hypotension & cardiac dysrrhythmias
Huntington’s Disease
DNS degenerative disease characterized by marked caudate nucleus atrophy & putamen & globus pallidus to lesser degree
Autosomal dominant
Huntington’s S/S
Progressive dementia
Chorea (involuntary jerking or writhing movement)
Tremors
Rigidity & contractures
Depression, aggressive outburst, mood swings
Difficulty w/ speech & swallowing
Huntington’s Treatment
Treat the choreiform movements
Antidepressants (Haldol)
Physical, occupational, & speech therapy
Huntington’s Anesthetic Considerations
Aspiration risk → RSI Prolonged response to Succinylcholine Sensitive to NDMR Avoid anticholinergics & Reglan Glycopyrrolate > Atropine
Lower Motor Neurons Disorders
Myasthenia gravis Lambert-Eaton Muscular dystrophy Myotonic dystrophy Mitochondrial disorders Guillain-Barre Spinal muscular atrophy
Myasthenia Gravis
Autoimmune destruction IgG antibodies against nAChR
Inactivation postsynaptic ACh receptors at NMJ
↓receptors & function degradation
complement-mediated damage to postsynaptic end plate
MG S/S
Diploplia & ptosis Fluctuating fatigue & weakness that improves after rest Mouth & throat muscle weakness Dyspnea w/ exertion Proximal muscle weakness
MG Treatment
Cholinesterase inhibitor (Pyridostigmine) Plasmapheresis Corticosteroids Immunosuppressants & immunoglobins Thymectomy
S/S exacerbated by pregnancy, infection, electrolyte imbalance, surgical & psychological stress, aminoglycoside antibiotics
MG Anesthetic Considerations
Aspiration risk Sensitive to NDMR Regional preferred (amide LAs) Avoid block > mid thoracic or interscalene or supraclavicular block d/t phrenic nerve paralysis RESISTANT to Succinylcholine 2mg/kg DOA ↑5-10min
Lambert-Eaton
Pre-synaptic defect
Antibodies attach to voltage-gated Ca2+ channels on the nerve terminal
↓ACh release at the motor end plate
Affects males > females
LEMS S/S
Proximal muscles 1° affected
Weakness generally worse in the morning & improves throughout the day
Respiratory & diaphragm muscles become weak
ANS dysfunction
- Orthostatic hypotension
- Delayed gastric motility
- Urinary retention
LEMS Treatment
3,4 DAP Guanidine hydrochloride Corticosteroids Immunosuppressants Plasmapheresis
LEMS Anesthetic Considerations
Sensitive to Succinylcholine & NDMR
Inadequate reversal w/ AChE
High risk postop respiratory failure
60% small cell carcinoma
Duchenne Muscular Dystrophy
X-linked recessive disorder Results from abnormal protein dystrophin production Affects males > females Presents between 3-5yo Rarely live past 30yrs
Duchenne MD S/S
Symmetric proximal muscle weakness manifested as gait disturbance “Gower sign”
Fatty infiltration typically causes muscle enlargement (particularly the calves)
Kyphoscoliosis
Respiratory muscle weakness
Cardiac muscle degeneration
Impaired GI hypo-motility, airway reflexes, &cardiac conduction
Cognitive impairment
Pulmonary HTN
Becker Muscular Dystrophy
X-linked recessive disorder
Partial dystrophin
Less common than Duchenne
Becker MD S/S
Present later in life (adolescence) Disease progresses more slowly Less severe Intellectual disability less common Proximal muscle weakness Prominent calf pseudohypertrophy Cardiac muscle degeneration Death r/t respiratory complications
MD Diagnosis
Genetic testing
↑CK levels
Muscle biopsy (rare)
MD Treatment
Surgery Physical therapy Steroids delay disease progression Biphosphates Mystatin inhibitors Gene modification Protease inhibitors Stem cell infusions
MD Anesthetic Considerations
Pre-anesthesia testing PFTs, echo, EEG, sleep apnea study
Avoid Succinylcholine & volatile anesthetics
Malignant hyperthermia syndrome characterized by rhabdomyolysis & hyperkalemia
Avoid preop w/ benzodiazepines & opioids
Positioning complications d/t kyphoscoliosis
Sensitive to NDMR - prolonged DOA
Local & regional anesthesia preferable
Aspiration risk
Myotonic Dystrophy
Hereditary skeletal muscle degenerative disease
Results in dysfunctional Ca2+ sequestration by SR
Na+ & Cl¯ channel dysfunction
Myotonic Dystrophy S/S
Weakness - facial, thoracic, intercostal, diaphragm, sternocleidomastoid, & distal limb
Inability to release/relax hand grip (myotonia)
Cardiomyopathy
Conduction defects 1st degree AV block
Dysphagia & slowed gastric emptying
Endocrine dysfunction
Central sleep apnea
Ptosis
Males (triad) - frontal balding, cataracts, & testicular atrophy
Myotonic Dystrophy Treatment
Procainamide Phenytoin Mexiletine Baclofen Dantrolene Carbamazepine Cardiac pacemaker
Myotonic Dystrophy Anesthetic Considerations
Avoid Succinylcholine
Aspiration risk
Volatile anesthetics may produce exaggerated myocardial depression
High volatile anesthetic concentrations potential to abolish myotonia
Questionable d/t association w/ MH
Anesthesia & surgery could aggravate cardiac conduction problems via ↑vagal tone
Neostigmine & Physostigmine aggravate myotonia
Sensitive to respiratory depressant
Maintain normothermia & avoid shivering
PFTs & EKG
Transthoracic pacing readily available
Mitochondrial Disorder
Heterogenous groups
Skeletal muscle energy metabolism disorders
Mitochondria produce energy required by skeletal muscle cells through the oxidation-reduction reactions of the electron transport chain & oxidative phosphorylation → ADP
Mitochondrial Disorder S/S
Abnormal fatigue w/ sustained exercise
Skeletal muscle pain & progressive weakness
Hearing loss & impaired vision
Balance & coordination problems
Seizures
Learning deficits
Organ problems - heart, liver, kidney, brain
Mitochondrial Disorder Treatment
Symptomatic Admin metabolites & cofactors Sodium bicarbonate Dichloroacetate Ketogenic diet
Mitochondrial Disorder Anesthetic Considerations
Prone to acidosis & dehydration Lactate level (avoid LR) Avoid continuous infusion Propofol Avoid Succinylcholine Maintain normothermia Use NDMR & LAs w/ caution Avoid Bupivacaine Avoid prolonged tourniquets
Guillain-Barre
Immunologic assault on myelin in the peripheral nerves particularly lower motor neurons
AP unable to be conducted
Motor endplate does not receive the incoming signal
Upward progression 2wks
Full recovery 4wks w/ some permanent paralysis remaining
Guillain-Barre S/S
Flaccid paralysis Begins in distal extremities & ascends bilaterally Intercostal muscle weakness Facial & pharyngeal weakness Sensory deficits Autonomic dysfunction common Cognition intact
Guillain-Barre Treatment
Plasmapheresis
IVIG
Steroids not useful
Guillain-Barre Anesthetic Considerations
Avoid Succinylcholine NDMR sensitivity ↑DVT risk Aspiration risk Exaggerated response to indirect sympathomimetics (A-line) Assess Na+ levels Slow position changes Avoid barbiturates → CV depression (autonomic dysfunction) Postop ventilation
Spinal Muscular Atrophy
Deletions or mutations in survival motor neuron gene on chromosome 5q13
SMN gene involved in RNA complex formation & trafficking out nucleus
Loss SMN function promotes apoptosis lower motor neurons - affects anterior spinal cord horn
SMA Type I
Most severe Infantile spinal muscular atrophy Autosomal recessive disorder Manifests w/in 3mos Rapidly progressive leading to death from respiratory complications usually by age 3
Difficulty sucking, swallowing, breathing, atrophy & fasciculation in tongue & limb muscles
SMA Type II
Autosomal recessive inheritance
Begins 6mos-1yo
Progressive more slowly than infantile form
Able to survive into adulthood
SMA Type III
Juvenile form
Develops after age 2
Weakness proximal limb muscles w/ relative sparing bulbar muscles (cranial nerves)
SMA Treatment
Spinraza Zolgensma 2019 Evrysdi 2020 PT Surgery Antibiotics
SMA Anesthetic Considerations
Pulmonary consultation
Difficult intubation d/t secretions, muscle weakness, contractures, & aspiration risk
Avoid Succinylcholine
Varying sensitivity to NDMR (longer DOA)
Regional controversial - neuraxial difficult/unreliable
Cautious w/ opioids
Postop respiratory support
Amyotrophic Lateral Sclerosis
Mixed motor neuron disease - upper & lower motor
Rapidly progressive motor neuron degeneration in corticospinal tract (1° descending upper motor neurons) & lower motor neurons in anterior spinal cord gray matter
Astrocytic gliosis replaces the affected motor neurons
ALS S/S
Spasticity Hyperreflexia & loss coordination Muscle weakness Fasciculations Atrophy often begins in hands Orthostatic hypotension Resting tachycardia Sensation remains intact Cognition WNL Bladder & bowel function not typically affected
ALS Treatment
Riluzole (NDMA receptor antagonist) - Only drug that reduces mortality Edaravone ↓ADLs decline Spasmolytics Analgesics
ALS Anesthetic Considerations
Avoid Succinylcholine Hyperkalemia risk ↑NDMR sensitivity Aspiration risk Consider postop mechanical ventilation ↑sensitivity to respiratory depressants Autonomic dysfunction w/ hemodynamic instability risk (A-line) Avoid spinal anesthesia d/t demyelination Induction → PEA
