Transcript Neuromuscular Emergencies

Neuromuscular Emergencies
Hanni Bouma
Objectives
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Discuss the approach to neuromuscular
respiratory failure
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Signs & Symptoms
Differential diagnosis
When to intubate
Brief overview of GBS & MG
Case 1
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26 yo previously healthy F p/w tingling in feet
since 1 week ago. Two days later noticed
difficulty climbing stairs, followed by
weakness of her arms. She is areflexic.
What percentage of patients with her disease
develop resp failure?
Case 1
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A) 5%
B) 10 to 20%
C) 25 to 50%
D) 70 to 85%
Case 2
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73 yo M adm w/ 3-month history of
progressive proximal weakness
1 day after muscle biopsy, noticed on rounds
to be breathless
What are we likely to see if this patient is in
resp failure?
Case 2
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A) Significant accessory muscle use
B) Pt complaining that “I can’t breathe!”
C) Shallow breaths; weak cough; neck flexor
weakness
D) Able to count to 40 in a single breath
Case 3
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63 yo M with limb-onset ALS since 2007 p/w
choking sensation, difficulty “getting air in”
Not on home BiPAP
No prior aspiration pneumonias; no fever, no
leukocytosis
Case 3
Case 3
Case 3
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Which of the following are you LEAST likely
to find in this patient?
A) FVC 1.1 L, MIP -20, MEP 30
B) MEP 40, MIP unable to complete
C) pH 7.35, pCO2 60, bicarb 36
D) FVC 4 L, MIP -90, MEP 100
What can cause generalized weakness
leading to resp failure?
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Spinal cord lesion
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Motor neuron lesion
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GBS, CIDP, critical illness polyneuropathy, Lyme disease, tick
paralysis, toxic
NMJ disorder
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ALS
Peripheral nerve lesion
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Cervical cord compression, transverse myelitis
MG, LEMS, botulism, organophosphate poisoning
Muscle lesion
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Polymyositis, dermatomyositis, critical illness myopathy,
hyperthyroidism, congenital myopathy (muscular dystrophy),
mitochrondrial myopathy
Mechanisms of NM resp failure
1) Upper airway obstruction:
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Facial, oropharyngeal, laryngeal weakness  mechanical
obstruction in supine position
impaired swallowing/secretion clearance  aspiration
2) Inspiratory muscle weakness atelectasis  V/Q
mismatch  hypoxia
3) Expiratory muscle weakness  weak cough/poor
secretion clearance  aspiration & pneumonia
4) Acute complications  PE, pneumonia, etc.
History
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Time course?
– progressive weakness over hours to days  GBS
– fluctuating weakness (on an hourly basis) present for
weeks/months  MG
Distribution of weakness?
– Proximal > distal (MG & GBS)
– Ascending in GBS
– Initally EOM/oropharyngeal muscle weakness, then
generalizes in botulism
Sensory Sx.?
– Distal paresthesias common in GBS
– No sensory inv’t in MG
History
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Pain?
– Low backache frequently in GBS; neck pain: C-spine
lesion?
Antecedent illness?
– 60% of GBS triggered by viral URT illness or C.jejuni gastro
– 40% of myasthenic crises triggered by infection
Medications
Exposure to fertilizers & pesticides?
– Organophosphate poisoning
Recent diet
– Botulism from home-canned goods
Exam: Signs of resp failure
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Tachycardia
Rapid, shallow breathing
Stridor
Weak cough, nasal voice, pooling of saliva (signs of bulbar
dysfunction)
Orthopnea (abnormal if VC drops >10% supine)
Staccato speech = the need to pause between words
Abdominal paradox = diaphragm weakness
weakness of neck & trapezius muscles (parallels diaphragm
weakness)
Single-breath count: ask them to inhale fully & count from 1 to
50. If <25, sign of severe impairment of VC
Mehta, S. “Neuromuscular disease causing acute respiratory failure.” Respiratory Care, 2006. 51 (9): 1016-1023.
Focused exam
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HEENT:
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look for pooled secretions
Swallow test
Dysphonia (nasal voice from palatal paralysis)
Dysarthria
Lungs
Diaphragm: observe/palpate for normal, outward
abdominal movement with inspiration
Cough strength
Count test (1 to 50)
Neuro exam
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CNs
Pupils:
 Reactivity may be lost in botulism or Miller-Fisher variant of GBS
– EOM:
 weakness + ptosis characteristic of MG, but also seen in MF, botulism,
etc.
– Face, palate, tongue, & neck strength
Motor exam:
– Fasciculations? (ALS, organophosphate poisoning); tone; power
(distribution of weakness? Fatigable weakness?)
Sensory:
– Distal sensory loss in GBS
– Sensory level at C-spine level w/ quadriparesis = C-spine lesion
Coordination:
– Ataxia in MF variant of GBS
Reflexes:
– Areflexia in GBS; usually preserved reflexes in MG
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Investigations
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Bedside PFTs: “20/30/40 rule”
– Vital capacity (max exhaled volume after full inspiration).
Normal = 60 ml/kg (4 L in 70 kg person). VC < 20 ml/kg (or
1 L) means intubation
– Max inspiratory pressure. Index of ability to avoid
atelectasis. Normal = <-50 cm H2O. MIP >-30 means
intubation
– Max expiratory pressure. Index of ability to cough/clear
secretions. Normal >60 cm H2O. MEP <40 means
intubation
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PFTs may be low if inadequate mouth closure from facial palsy, and may
fluctuate in MG
Investigations
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ABG:
– Hypercarbia (PCO2 > 45 mmHg) =
hypoventilation
* PCO2 often normal or low until late in NM resp
failure
– Hypoxia (PO2 < 75 mmHg) = V/Q mismatch 
usually atelectasis or pneumonia in this
setting
Investigations
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Basic labs (CBC, SMA-10, LFTs, CK)
CXR
EKG (electrolyte D/O; GBS ass’d w/
dysautonomia  arrhythmias)
General care
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Electrolytes: low potassium, high magnesium & low
phosphate  exacerbate muscle weakness
Serial PFTs (MIP/MEP/FVC) bid to qid
Chest physio, suctioning & incentive spirometry
DVT prophylaxis
HOB elevation
NPO if bulbar weakness; NG or Dobhoff feeding
Bowel/bladder: paralysis predisposes to
constipation; GBS pts may have urinary retention
Determine:
If resp failure is imminent
– If ICU should be involved
– What is the localization?
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Predictors of need for MV
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20/30/40 rule
or a reduction in VC, MIP, MEP by >30%
PO2 <70 mmHg on RA or PCO2 >50 mmHg w/ acidosis
Dysarthria, dysphagia, impaired gag reflex
In GBS:
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Time from onset to admission < 7 days
Inability to cough
Inability to stand
Inability to lift elbows or head
LFT increases
Presence of autonomic dysfxn
Sharshar T, Chevret S, Bourdain F, Raphael JC. Early predictors of mechanical ventilation in Guillain-Barre´
syndrome. Crit Care Med 2003;31(1):278–283.
Intubation: things to think about
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Code status?
Identify imminent resp failure early to avoid
emergency intubation
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Minimizes atelectasis/pneumonia
Minimizes complications of intubation specific to GBS &
MG:
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Dysautonomia: can cause severe bradycardia, BP shifts,
profound hypotension w/ sedatives
Denervated muscle: can cause fatal hyperkalemia with use of
succinylcholine
Avoid depolarizing NM blockers
Small doses of benzos
NPPV?
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Few studies on its use in GBS & MG
Inappropriate if upper airway function
severely impaired or hypercapnic resp failure
GBS
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Most common cause of acute or subacute gen’d
paralysis
Monophasic AIDP: autoimmune attack against
surface antigens on peripheral nerves
Develops 5 days to 3 weeks after resp/GI infection in
60%
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Campylobacter jejuni (26%)
Viral URTI, influenza
EBV, CMV, VZV, HIV, hep A & B, coxsackie
Other precipitants: immunization, pregnancy,
surgery, Hodgkin’s disease
Presentation
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Sensory:
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Motor:
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Symmetric; evolves over days to 1-2 wks
Ascending: LE before UE; proximal> distal
May progress to involve trunk, intercostals, neck, bulbar, B/L FNs
Median duration from onset to max weakness 12 days
Reflexes: reduced, then absent
Autonomic instability:
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distal paresthesias/numbness (earliest Sx.)
Reduced vibration/proprioception
Sinus tachy/brady, arrhythmias, labile BP (esp hypertension),
urinary retention, anhydrosis
Other: low backache very common, myalgias
Investigations
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EMG:
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Reduced conduction velocities
Loss of F waves
Conduction block in motor nerves
Reduced motor amplitudes: 2° axonal damage  worse Px.
CSF:
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High protein (may be normal in first 2 days)
No cells or few lymphs
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10% have 10-50 lymphs
Management
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Admit for observation (potential for deterioration)
Determine if resp failure imminent
Dysautonomia: most frequently sustained HTN &
tachycardia
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Esp in older pts w/ CAD, consider Labetolol
Hypotension in 10%  fluids, pressors
PLEX (4-6 Rx. q1-2d) & IVIG (0.4g/kg/d x 5 d):
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Equally effective
PLEX useful in first 2 weeks; benefit less clear after that
Steroids no proven benefit
Course
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Progression over 1-4 weeks
Plateau: 2-4 months
Recovery: few wks to months
Mortality 3-5%
Poor prognosis:
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Resp failure requiring intubation
Advanced age
Very low distal motor amplitudes (axonal damage)
Rapidly progressive weakness over 1 week
MG
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Ab-mediated attack on nicotinic Ach rec 
defective transmission across NMJ
Bimodal: F 20-30 yo; M 50-60 yo
2 autoimmune forms
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Ach receptor Ab+: 80% with generalized MG &
50% with ocular MG
Anti-MuSK Ab+: 50% of patients who are Ach rec
Ab negative; typically female with prominent
bulbar weakness
Presentation
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Motor:
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Fluctuating, fatigable weakness involving eyes (90%),
face/neck/oropharynx (80%), limbs (60%)
Limbs rarely affected in isolation
Rest restores strength (at least partially)
Usually insidious onset
Sensory: normal
Reflexes: preserved
Thymic abnormalities:
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Malignant thymoma in 10-15% (more severe disease)
Thymic hyperplasia in 50-70%
Myasthenic Crisis
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Defined by resp failure requiring ventilatory
assistance
Occurs in 20-30%; mortality 5%
Common precipitants:
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Infection in 40% (esp respiratory)
Pregnancy
Medications
Aspiration
Surgery
Emotional upset, hot environment
Drugs that exacerbate MG
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Antibiotics:
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Cardiac:
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Phenytoin, CBZ
Antipsychotics, lithium
Thyroid hormones
Magnesium toxicity
Iodinated contrast agents
Muscle relaxants
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All beta-blockers
Calcium channel blockers
Class I anti-arrhythmics (quinidine, procainamide)
Anticonvulsants:
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Aminoglycosides (genta, tobra)
Fluroquinolones (cipro)
Macrolides (erythromycin, azithro, tetracycline, doxycycline)
Baclofen
Long-acting benzos
**Too much anticholinesterase
Investigations
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Ach receptor Abs
Anti-MuSK Abs
EMG:
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Repetitive nerve stimulation: >10% decrement in amplitude
betw 1st & 5th CMAP
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Single-fiber: “jitter” (variation in time interval betw firing of
muscle fibers in same motor unit)
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Sens/spec 90% when weak, proximal muscles stimulated;
<50% sens in pts w/o limb weakness
Sens >95% for MG but not specific
Edrophonium (Tensilon) test:
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Not recommended in suspected crisis
Management
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Determine if resp failure imminent
Stop exacerbating meds
Treat infection
Symptomatic therapy (mild-moderate weakness):
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Short-term disease suppression:
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Cholinesterase inhibitors (Mestinon)
To hasten clinical improvement in hospitalized pts w/ crisis or impending crisis; preoperatively; chronic refractory disease
PLEX: improvement w/i days, but lasts only 2-4 wks
IVIG: benefit may last up to 30 days
Comparable benefits
Long-term immunosuppression:
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When weakness is inadequately controlled by Mestinon
Prednisone
Azathioprine (if steroid failure or excessive SE)
Key points
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20/30/40 rule
Identify pts at risk for resp failure EARLY to
avoid emergency intubation
Don’t wait for pts to complain of SOB before
doing bedside PFTs