Neuromuscular Disorders
Dwayne McClerklin, MD
Assistant Professor
Department of Anesthesiology and Perioperative Medicine
MUSC
Myasthenia Gravis
Path: Autoimmune destruction of the
postsynaptic Ach receptor
S/Sx: muscle weakness, easy fatiguability ;
symptoms worsen with exercise and
improve with rest. With bulbar
involvement, laryngeal and pharyngeal
muscle weakness results in dysarthria,
difficulty chewing/ swallowing, problems
clearing secretions, or pulmonary
aspiration.
Myasthenia Gravis
Type I
ocular muscle weakness
Type II
mild nonocular weakness
Type III
Moderate nonocular muscle
weakness
Severe nonocular muscle
weakness
Tracheal intubation and
mechanical ventilation
Type IV
Type V
Myasthenia Gravis
Rx: Acetylcholinesterase Inhibitors (AchEI)
increase the amount of acetylcholine at the
neuromuscular junction through inhibition of
end-plate acetylcholinesterase
Cholinergic crisis results from excessive AchEI
dosing and is characterized by increased
weakness and excessive muscarinic effects
Edrophonium test- differentiates cholinergic from
muscarinic crisis. Sx of muscarinic crisis worsen
with edrophonium administration
Myasthenia Gravis
Anesthetic Considerations
Preoperative continuation of AchEI
controversial (pros- potential decreased
postop weaknes; cons- altered action of
NMBAs, bowel hyperactivity)
Pts may be at increased risk of aspiration,
respiratory depression (go easy with
premedications)
Myasthenia Gravis
Deep anesthesia with a volatile agent may
produce favorable conditions for tracheal
intubation
Pts demonstrate resistance to depolarizing
NMBAs, proneness to Phase II blockade
Pts sensitive to nondepolarizing NMBAs
Myasthenia Gravis
Patients who have myasthenia gravis are at
great risk for postoperative respiratory failure
Disease duration of more than 6 years,
concomitant pulmonary disease, a
peakinspiratory pressure of < –25 cm H2O (ie,
–20 cm H2O), a vital capacity < 4 mL/kg, and a
pyridostigmine dose > 750 mg/d are predictive
of the need for postoperative ventilation
Eaton Lambert Syndrome
Path: Caused by failure of presynaptic Ca2+
entry (which normally stimulates release of
Ach); associated with small cell cancer of the
lung
S/Sx: muscle weakness that improves with
exercise; minimal improvement with AchEI
Rx: Aminopyridines (presynaptic K+ channel
blockers which prolong the AP, increasing
Ca2+ influx and Ach release)
Eaton Lambert Syndrome
Anesthetic Considerations
Pts with ELS are sensitive to both
depolarizing and nondepolarizing NMBAs
Deep anesthesia with volatile agents is
usually sufficient for intubation
Muscular Dystrophies
Duchenne’s Muscular Dystrophy
An X-linked recessive disorder,
Duchenne's muscular dystrophy affects
males almost exclusively
Affected individuals produce abnormal
dystrophin, a protein found on the
sarcolemma of muscle fibers.
Muscular Dystrophies
Duchenne’s Muscular Dystrophy
S/Sx: Progressive proximal muscle
weakness (gait disturbance) and fatty
infiltration of calf muscles; respiratory
muscle weakness (atelectasis, restrictive
lung disease, impaired cough);
cardiomyopathy, papillary muscle
dysfunction leading to MR
Muscular Dystrophies
Duchenne’s Muscular Dystrophy
Dx: Elevated serum creatine kinase (10100x normal), elevated serum myoglobin
levels; Muscle biopsy is definitive
Rx: Supportive care; corticosteroids;
spinal rodding and fusion to improve
mobility and comfort
Muscular Dystrophies
Duchenne’s Muscular Dystrophy
Anesthetic considerations: assess degree
of weakness, multisystem involvement; pts
may be an aspiration risk; avoid Sux (risk
of hyperkalemic arrest, MH); sensitivity to
nondepolarizing NMBAs may be increased
Muscular Dystrophies
Myotonic Dystrophy
Myotonia-slowing of relaxation after
muscle contraction in response to
electrical or percussive stimuli.
Myotonic Dystrophy (MD) is the most
common cause of myotonia
Muscular Dystrophies
Myotonic Dystrophy
S/Sx:Myotonia is the principal
manifestation early in the disease, but as
the disease progresses, muscle weakness
and atrophy become more prominent.
Other manifestations include
cardiomyopathy, gastric hypomotility, and
alveolar hypoventilation
Muscular Dystrophies
Myotonic Dystrophy
Anesthetic Considerations- Pts are
aspiration risks; avoid premedication due
to proneness to hypoventilation; avoid
Sux; Cis is a good choice; Neostigmine
can exacerbate myotonia; avoid
postoperative shivering
Myotonias
Myotonia Congenita
Path:caused by mutations of a gene on
chromosome 7q35 encoding a chloride
channel of the skeletal muscle fiber
surface membrane.
S/Sx:. The disease is confined to skeletal
muscle and produces no, minimal, or
nonprogressive weakness. There is no
cardiac involvement
Myotonias
Paramyotonia Congenita
S/Sx:Symptoms of paramyotonia congenita
include transient stiffness (myotonia) and,
occasionally, weakness after exposure to
cold temperatures;The stiffness worsens
with activity, in contrast to true myotonia,
thus the term "paramyotonia."
Myotonias
Anesthetic Considerations
Pts may demonstrate anabnormal response to
Sux and troublesome intraoperative myotonic
contractions (not associated with MH)
Avoid hypothermia.
NMBAs may paradoxically cause generalized
muscle spasms, including trismus, leading to
difficulty with intubation and ventilation
Periodic Paralysis
Hypokalemic Periodic Paralysis
Path: abnormalities in membrane transport
of Na+ and K+, making muscle excitation
difficult
S/Sx: autosomal dominant disorder
manifesting as acute bouts of weakness/
paralysis of the extremities and trunk
muscles (spares diaphragm) lasting about 3
hours
Periodic Paralysis
Hypokalemic Periodic Paralysis
Episodes are most common in the early
morning and can be precipitated by
strenuous exertion, cold weather, high
carbohydrate meals, or glc and insulin
administration. Mild exertion can actually
prevent or delay paralysis.
Periodic Paralysis
Hyperkalemic Periodic Paralysis
Path:paralysis is triggered by abnormal
inactivation of Na+ channels by a mild increase
in K+. Na+ and water flow into the cells with
prolonged depolarization; more frequent
attacks than hypokalemic variant
S/Sx: weakness triggered by fasting, cold
weather, rest following exercise K+ intake;
bradycardia
Periodic Paralysis
Anesthetic Considerations
Anesthetic management is directed toward
preventing attacks
Check K+ often
Glucose-containing intravenous fluids should
not be used in patients with hypokalemic
paralysis, whereas such solutions may benefit
patients with hyperkalemic and normokalemic
paralysis
Periodic Paralysis
Anesthetic Considerations
In patients with periodic paralysis, the
response to NMBAs is unpredictable
Pts with hypokalemic variant are sensitive to
nondepolarizing NMBAs
Sux is contraindicated in the hyperkalemic
variant
Maintain normothermia