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Neuromuscular Disorders
Saad Al Juma
R3
In MNL : Poliomyelitis is the protypical disease In Poliomyelitis weakness can be
asymmetrical or more often symmetrical The cerebrospinal fluid analysis resembles
that of aseptic meningitis. Patients initially have a clinical picture similar
to that of viral meningitis
In MNL : Amyotrophic lateral sclerosis is the
prototypical disease In Poliomyelitis weakness can be symmetrical
or more often asymmetrical The cerebrospinal fluid analysis resembles
that of viral meningitis. Patients initially have a clinical picture similar
to that of viral meningitis…..
In Amyotrophic lateral sclerosis It affects the anterior horn cells and results in
lower motor neuron disease without sensory involvement
Results from a degeneration of the motor neuron with sensory involvement.
complain of dysarthria or ptosis findings include hyporreflexia, muscle
wasting, and fasciculation Pain is not a component of the clinical
picture….
In Amyotrophic lateral sclerosis Poliomyelitis affects the anterior horn cells
and results in lower motor neuron disease without sensory involvement
Results from a degeneration of the motor neuron without sensory involvement.
complain of dysarthria or dysphagia findings include hyperreflexia, muscle
wasting, and fasciculation Pain is not a component of the clinical
picture….
In MNL all are true except : lesions at the level of the brainstem or above
produce bilateral weakness bilateral weakness caused by lesions above
the spinal cord is associated with a change in mental status or cranial nerve involvement
Lesions of the central nervous system result in spasticity, hyperreflexia, and extensor plantar reflexes
bilateral upper motor neuron signs with normal mental status, neuroimaging should focus on looking for a lesion in the spinal cord
In MNL : lesions at the level of the brainstem or above
produce unilateral weakness bilateral weakness caused by lesions above the
spinal cord is generally associated with a change in mental status or cranial nerve involvement
Lesions of the central nervous system result in spasticity, hyperreflexia, and extensor plantar reflexes
when bilateral upper motor neuron signs are found in conjunction with normal mental status, diagnostic testing including neuroimaging should focus on looking for a lesion in the spinal cord
In Neuropathies , all are true EXCEPT : a grip strength or foot-drop may be noted first patients usually note a slowly progressive
course of symptoms. A disorder of transmission often leads to
increased production of ACh receptors. Patients usually have intact sensation
sensation.
In Neuropathies : a grip strength or foot-drop may be noted first patients usually note a slowly progressive
course of symptoms. A disorder of transmission often leads to
increased production of ACh receptors. Patients exhibit varying degrees of altered
sensation
In Myopathies , all are true EXCEPT: Myopathies produce generalized, symmetrical
weakness muscle tone is usually diminished, but
sensation is preserved. Generally cause muscle pain and tenderness Reflexes are present but diminished
In Myopathies Myopathies produce generalized, symmetrical
weakness muscle tone is usually diminished, but
sensation is preserved. Metabolic disorders affecting muscle strength
are painless in nature Reflexes are present but diminished
DISEASE HISTORY STRENGTHDEEP
TENDON REFLEX
SENSATION WASTING
MyelopathyTrauma,
infection, cancer
Normal to decreased
IncreasedNormal to decreased
No
Motor neuron disease (ALS)
Progressive difficulty
swallowing, speaking, walking
Decreased Increased Normal Yes
Neuropathy
Recent infection
Ascending weakness
Normal or decreasedDistal > proximal
Decreased
Decreased
Yes
Neuromuscular junction disease
Food (canned goods)
Tick exposureEasy
fatigability
Normal to fatigue
Normal
Normal
No
Myopathy
Thyroid diseasePrevious similar
episodes
DecreasedProximal >
distal
Normal
Normal
Yes
In MG all the following are true except: Normally, vital capacity values range from 60
to 70 mL/kg. the forced vital capacity reaches 15 mL/kg,
intubation is necessary Arterial blood gas is helpful as most of the
patients have sufficient protective reserve and hypercapnia develps early
presence of swallowing and a strong cough suggests that the patient has sufficient protective and ventilatory reserve
In MG : Normally, vital capacity values range from 60
to 70 mL/kg. the forced vital capacity reaches 15 mL/kg,
intubation is necessary Arterial blood gas is not necessarily helpful
because functional reserve can be severely diminished by the time a patient develops either hypercarbia or hypoxia
presence of swallowing and a strong cough suggests that the patient has sufficient protective and ventilatory reserve
In Diseases of the Neuromuscular Junction Repeated stimulation leads to diminishing motor strength, which is caused by :
the blockage of the receptors as in organophosphate poisoning
a decrease in the amount of ACh released as in botulism
inactivating Ach by irreversibly binding with it as in MG
Down regulation of the Ach receptors as in Atropinized patients
In Diseases of the Neuromuscular Junction Repeated stimulation leads to diminishing motor strength, which is caused by :
the blockage of the receptors as in MG a decrease in the amount of ACh released as
in botulism inactivating Ach by irreversibly binding with it
as in organophosphate poisoning Down regulation of the Ach receptors as in
Atropinized patients
decrease in the release of ACh may produce except decreased visual acuity low-grade fever dry, flushed skin Bradycardia urinary retention
decrease in the release of ACh may produce: decreased visual acuity low-grade fever dry, flushed skin Tachycardia urinary retention
All are true about Myopathies , except: generalized, symmetrical weakness Reflexes are present muscle tone is usually diminished sensation is lost Are always painful
All are true about Myopathies : generalized, symmetrical weakness Reflexes are present muscle tone is usually diminished sensation is preserved Are always painful
Lambert-Eaton myasthenic syndromeall are false except : 50% of cases are associated with non small
cell carcinoma of the lung Clinically includes weakness that improves
with use of muscles….. autonomic dysfunction, most commonly seen
as flushed skin. Management with IVIG has been reported to
be sufficient.
Lambert-Eaton myasthenic syndrome: 50% of cases are associated with small cell
carcinoma of the lung Clinically includes weakness that improves
with use of muscles autonomic dysfunction, most commonly seen
as dry mouth. Management primarily focuses on treating the
underlying neoplastic disorder
Regarding MG , all are true except: Age of onset is bimodal MG results from autoantibodies directed
against the nicotinic acetylcholine receptor (AChR) at the neuromuscular junction
Ocular symptoms are often the first manifestation of MG
Bulbar muscles are spared
Regarding MG : Age of onset is bimodal MG results from autoantibodies directed
against the nicotinic acetylcholine receptor (AChR) at the neuromuscular junction
Ocular symptoms are often the first manifestation of MG
Bulbar muscles may be involved
What is Edrophonium test ?
What is Edrophonium test ?Edrophonium (Tensilon) test:
measure distance from upper to the lower eyelid before and after IV edrophonium (AChE blocking agent)
give test dose first 1-2mg IV , if no ADR/no improvement 3mg, if no response 5mg (max 10mg) watch for bradycardia (only perform when pt on monitor with
Atropine at bedside DUE TO BRADY AND SECRETIONS ISSUES.)
contraindicated in COPD/asthma pts because of risk of secretions.
reports of FP with botulism
What is Ice pack test ?
What is Ice pack test ? it is applied to the affected eye for
approximately 2 minutes the distance between the lids is measured
again prospective evaluation of the ice bag
approach found the test result to be positive (an improvement in distance of at least 2 mm) in 80% of patients with MG and in no patients without MG.[7]
defined as respiratory failure leading to mechanical ventilation
Occurs in 15 to 20% of patients with MG within the first 2 years of disease onset precipitant may not be found in 3 % of cases
In Myasthenic Crisis all are true Except:
In Myasthenic Crisis : defined as respiratory failure leading to
mechanical ventilation Occurs in 15 to 20% of patients with MG within the first 2 years of disease onset precipitant may not be found in 30% of cases
BONUS QUESTION
Medications precipitate MG crisis
Medications precipitate MG crisisCVS ABX Others
Beta-blockers Aminoglycosides Phenytoin
Calcium channel blockers Tetracyclines Neuromuscular blockers
Quinidine Clindamycin Corticosteroids
Lidocaine Lincomycin
Thyroid replacementProcainamide
Polymyxin B
Colistin
Regarding MG Management all are true EXCEPT: in the setting of acute exacerbation of MG ,
The use of intravenous pyridostigmine is recommended
the initiation of corticosteroids in patients with moderate to severe weakness may improve the outcome
Thymectomy is recommended for patients younger than 60
IVIG is preferred over PE due to the side effects of the later.
Regarding MG Management: in the setting of acute exacerbation of MG ,
The use of intravenous pyridostigmine is NOT recommended
the initiation of corticosteroids in patients with moderate to severe weakness may improve the outcome
Thymectomy is recommended for patients younger than 60
IVIG is preferred over PE due to the side effects of the later.
Regarding P.E in M.G : The fall in AChR levels is not associated with
improvement in symptoms of MG. complications include hypotension or
anticoagulation. It is safe in children. many case series showed long-term benefit in
myasthenic crisis.
Regarding P.E in M.G : The fall in AChR levels is associated with
improvement in symptoms of MG. There is a risk of complications from
hypotension or anticoagulation. Because of safety concerns, clinical trials have
not been done in children. Although there are no randomized controlled
studies, a review yielded many case series with short-term benefit, especially in myasthenic crisis.
Regarding Botulism , all are true except: Most common type is infant Botulism Clostridium botulinum is an anaerobic, spore-
forming bacterium types A, B, and C toxins cause human
disease…. botulinum toxin works by binding irreversibly
to the presynaptic membrane of peripheral and cranial nerves, inhibiting the release of ACh at the peripheral nerve synapse
Regarding Botulism : Most common type is infant Botulism Clostridium botulinum is an anaerobic, spore-
forming bacterium types A, B, and E toxins cause human
disease…. botulinum toxin works by binding irreversibly
to the presynaptic membrane of peripheral and cranial nerves, inhibiting the release of ACh at the peripheral nerve synapse
In Botulism , all are true except : There is no pain The onset of symptoms is 6 to 48 hours after
the ingestion of tainted food descending, symmetrical, flaccid paralysis diplopia, dysarthria, and dysphagia are the
first signs Pupils are often fixed and reactive to light…
In Botulism : There is no pain The onset of symptoms is 6 to 48 hours after
the ingestion of tainted food descending, symmetrical, flaccid paralysis diplopia, dysarthria, and dysphagia are the
first signs Pupils are often dilated and not reactive to
light…
Regarding Botulisim antitoxin there is a risk of anaphylaxis and serum
sickness It is known to decrease ventilator dependence the antitoxin should be administered once the
toxin can be identified in serum and stool the antitoxin should be administered as soon
as possible An intravenous human botulism immune
globulin (BIG-IV) has been developed for treatment of wound related botulism
Regarding Botulisim antitoxin there is a risk of anaphylaxis and serum
sickness although it is not clear that the antitoxin
decreases ventilator dependence the antitoxin should be administered as soon
as possible (clinical findings and exclusion of other processes)
An intravenous human botulism immune globulin (BIG-IV) has been developed for treatment of infantile botulism
In Tick Paralysis, all are true except an acute, ascending, flaccid motor paralysis Usually starts after 6-12 days from female tick
has attached and begun to feed fixed and dilated pupils associated with the
disease. Intubation may be necessary after tick
removal
In Tick Paralysis an acute, ascending, flaccid motor paralysis Usually starts after 1-2 days from female tick
has attached and begun to feed fixed and dilated pupils associated with the
disease. Intubation may be necessary after tick
removal
In Thyrotoxic Periodic Paralysis , all are true EXCEPT: It is due to decreased sodium-potassium
adenosine triphosphatase activity Treatment of the hyperthyroid symptoms
helps the treatment of the paralysis There is probably a genetic feature underlying
this disorder all patients have thyroid function testing done
after a first episode of hypokalemic paralysis
In Thyrotoxic Periodic Paralysis It is due to increased sodium-potassium
adenosine triphosphatase activity Treatment of the hyperthyroid symptoms
helps the treatment of the paralysis There is probably a genetic feature underlying
this disorder all patients have thyroid function testing done
after a first episode of hypokalemic paralysis
In Familial Periodic Paralysis all are true EXCEPT: autosomal-dominant disorders of ion channels intermittent attacks of flaccid extremity
weakness associated with either hyperkalemia or hypokalemia
bulbar and respiratory muscles may be affected. The onset of symptoms often follows a high
carbohydrate intake and a period of rest. An electrocardiogram, which should be done
immediately
In Familial Periodic Paralysis:
autosomal-dominant disorders of ion channels intermittent attacks of flaccid extremity
weakness associated with either hyperkalemia or hypokalemia
bulbar and respiratory muscles not affected. The onset of symptoms often follows a high
carbohydrate intake and a period of rest. An electrocardiogram, which should be done
immediately
Which of the following statements is true?
a. Herpes zoster is often associated with motor dysfunction with or without a rash.
b. Acute rabies infection typically begins as a Ramsay-Hunt syndrome before progressing to severe throat spasm and to cardiac and renal failure.
c. Weakness or diplopia when fatigued may be the only complaint with multiple sclerosis.
d. Treatment for polymyositis is early administration of systemic steroids.
e. Serum calcium should be measured in patients with recurrent generalized weakness that follows periods of heavy exertion or that is present upon awakening.
The answer is c. Ramsay-Hunt syndrome refers to herpes zoster involving the
tympanic membrane, ear canal, and other areas in the distribution of the sensory branches of the facial nerve.
Herpetic zoster may result in motor abnormalities in up to 25% of cases.
Weakness or diplopia only on exertion is a common complaint in early cases of multiple sclerosis. Another early presenting sign is retrobulbar neuritis; in fact, 50–75% of cases occur in patients who develop multiple sclerosis.
Steroids may transiently exacerbate weakness in patients with polymyositis and should not be started on patients who will be discharged from the ED.
Acute periodic paralysis appears to involve abnormalities in cellular function, possibly related to potassium transport. The disease is most common in young men. No specific physical findings may be found and it is often misdiagnosed as hysterical in origin
2. A 34-year-old woman with known myasthenia gravis presents in respiratory distress. She is unable to move without assistance. Her vital signs are: temperature 36◦C (96.8◦F), heart rate 50/min, blood pressure 100/60 mm Hg, respiratory rate 35/min and shallow. She is drooling and has upper airway rhonchi and bilateral wheezing. Her respiratory rate appears to be decreasing. You immediately:
a. Administer 2–4 mg of intravenous edrophonium.b. Perform endotracheal intubation.c. Administer 1 mg of atropine; if there is an
improvement in her wheezing, administer pralidoxime.
d. Start an intravenous atropine drip.e. Arrange emergent hyperbaric therapy.
The answer is b
You should be able to differentiate a myasthenic crisis from a cholinergic crisis.
Both can present with progressive muscle weakness and respiratory depression, dysphagia, and other physical signs. Bradycardia, wheezing, and salivation suggest cholinergic crisis.
A common error is to mistake a cholinergic as a myasthenic crisis and administer additional acetylcholinesterase inhibitor.
The immediate treatment for either type is ABCs and intubation at the first clinical signs of respiratory failure.
In a cholinergic crisis, atropine can be used for the muscarinic symptoms, but it is not a substitute for airway management and ventilatory assistance.
A 13-year-old girl presents with a 3-day history of malaise, low-grade fever, and double vision with unilateral ptosis. The potential diagnosis of botulism is best supported by finding:
a. Acute renal failure.b. Cardiac failure.c. Bilateral numbness of hands and feet.d. Acute urinary retention.e. Pseudomembranous pharyngitis.
The answer is d Both botulism and diphtheria may present with
acute bulbar nerve palsies, weakness of any or all extremities, and cholinergic manifestations, such as urinary retention and colicky pain.
In both diseases, the most common early neurologic findings are ptosis, double vision, and difficulty in accommodation.
Diphtheria is an acute febrile illness. A primary symptom is a severe pseudomembranous pharyngitis presenting with severe throat pain and excessive saliva production.
In diphtheria, cardiotoxic and renal abnormalities are direct results of the elaborated bacterial toxin.
A 34-year-old woman with myasthenia gravis presents with flank pain and fever of 103.4◦F. She is allergic to penicillin, and despite boluses of intravenous fluid and antibiotic therapy, she becomes hypotensive. A medicine that you can safely use in her management is:
a. Gentamicin.b. Vecuronium.c. Lidocaine.d. Procainamide.e. Succinylcholine.
The answer is c Aminoglycoside antibiotics have some curare-
type effects on the motor endplate; if they are used in the myasthenic patient, the physician should be prepared to treat paralysis and respiratory arrest. Obviously, these patients are more susceptible to muscle-paralyzing agents as well. Phenytoin, quinidine, procainamide, and lithium can also adversely affect patients with myasthenia gravis.
Curare (Chondodendron tomentosum),
•a South American vine native to the Amazon Basin. •The undersides of the leaves are white-tomentose. •An extract from the bark and stems is the source of a potent isoquinoline alkaloid used in the deadly poison curare. Amazonian Indians use the gummy extract to coat the poison darts of their blowguns. The alkaloid D-tubocurarine blocks acetylcholine receptor sites at neuromuscular junctions, causing relaxation and paralysis of muscles, including respiratory organs and the heart.• In fact, D-tubocurarine has been used to relax the heart muscle during open heart surgery. •It has also been used to treat the spastic paralysis of tetanus toxin from the bacterium Clostridium botulinum. Tetanus toxin causes uncontrollable muscle contraction throughout the body.
Neuropathy is differentiated from myopathy in that:
a. Neuropathies progress proximally.b. Myopathies affect distal and proximal muscle
groups equally.c. Myopathies and neuropathies both have
prominent sensory findings.d. Myopathies often have striking weakness of
the small muscles of the hands.e. Myopathies have relatively preserved deep
tendon reflexes.
The answer is a Neuropathies tend to have the following
characteristics: proximal progression of symptoms sensory deficits often in a stocking glove
distribution early loss of DTRs.
Myopathies characteristically present with proximal motor weakness myalgias delayed loss of DTRs CPK enzymes may be elevated.
There are exceptions to these generalizations.
Lambert-Eaton Myasthenic Syndrome results from an autoimmune attack directed against the voltage-
gated calcium channels (VGCCs) on the presynaptic motor nerve terminal.
This results in a loss of functional VGCCs at the motor nerve terminals. The number of quanta released by a nerve impulse is diminished.
However, because presynaptic stores of ACh and the postsynaptic response to ACh remain intact, rapid repetitive stimulation or voluntary activation that aids in the release of quanta will raise the endplate potential above threshold and permit generation of muscle action potential.
As neuromuscular transmission is completed at additional neuromuscular junctions, a transient increase will occur in the strength of the muscle.
Parasympathetic, sympathetic, and enteric neurons are all affected. Clinically, this phenomenon is noted by the appearance of previously
absent tendon reflexes following a short period of strong muscle contraction by the patient.
Myasthenia Gravis Autoantibodies (immunoglobulin G [IgG]) develop against ACh nicotinic
postsynaptic receptors for unknown reasons, although certain genotypes are more susceptible.2
Cholinergic nerve conduction to striated muscle is impaired by a mechanical blockage of the binding site by antibodies and, ultimately, by destruction of the postsynaptic receptor.
Patients become symptomatic once the number of ACh receptors is reduced to approximately 30% of normal. The cholinergic receptors of smooth and cardiac muscle have a different antigenicity than skeletal muscle and are not affected by the disease.
The role of the thymus in the pathogenesis of myasthenia gravis is not entirely clear, but 75% of patients with myasthenia gravis have some degree of thymus abnormality (eg, hyperplasia in 85% of cases, thymoma in 15% of cases). Given the immunologic function of the thymus and the improvement in the clinical condition of patients following thymectomy, the thymus is suspected to be the site of autoantibody formation. However, the stimulus that initiates the autoimmune process has not been identified