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Neuromuscular Emergencies. July 28, 2010 Sandra Derghazarian. Outline. Approach to rapidly progressing LMN weakness Myasthenic crisis GBS. Intro. Three major tasks: Assess stability, signs of imminent resp failure Generate differential diagnosis Knowledge of localisation

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neuromuscular emergencies

Neuromuscular Emergencies

July 28, 2010

Sandra Derghazarian

outline
Outline
  • Approach to rapidly progressing LMN weakness
  • Myasthenic crisis
  • GBS
intro
Intro
  • Three major tasks:
    • Assess stability, signs of imminent resp failure
    • Generate differential diagnosis
      • Knowledge of localisation
      • Knowledge of major disorders
    • Determine management
brief review of anatomy
Brief Review of Anatomy
  • Motor unit anatomy
    • Anterior horn cell
    • Its motor axon
    • The synaptic cleft
    • The muscle fibers it innervates
  • Remember sensory and autonomic systems
    • Many disorder with rapidly progressing peripheral neuropathic weakness will have sensory loss and dysautonomia
classification
Classification
  • Motor neuron
    • Loss of anterior horn cells
  • Motor axon
    • Disruption of myelin sheath
    • Axonal degeneration
  • Neuromuscular junction
    • Pre-synaptic (e.g. Release of Ach)
    • Post-synaptic (e.g. Abnormalities of Ach receptor)
  • Muscle
    • Membrane, contractile elements
    • Genetic or acquired secondary (infex, inflamm, vasc.)
approach to determining cause of weakness
Approach to Determining Cause of Weakness
  • Knowledge of some of the possible disorders
  • Focused history
  • Physical exam
  • Lab studies
history key elements
History – Key Elements
  • Pre-existing NM disorder?
    • MG – exacerbation 2ary systemic illness, medication
    • ALS – accelerated phase, decompensation 2ary pneumonia
  • Pre-existing systemic disorder?
    • Malignancy, CTD, sepsis
  • What drugs is pt taking?
  • Any recent illness?
  • Diet in last 48 hours?
    • Shellfish (saxitoxin, brevetoxin)
    • Home-canned goods (botulinum toxin)
  • Any possible exposure to tick bite, snake bite?
  • Any sensory or autonomic symptoms?
drugs
Drugs
  • Diuretics
    • Hypokalemia
  • Corticosteroids, statins, colchicine, cyclosporine, cocaine, chloroquine, L-tryptophan, penicillamine, zidovudine
    • Myotoxic effect
  • Amiodarone, cytarabine, streptokinase
    • Demyelinating neuropathy
  • Magnesium-containing antacids with pre-existing renal insufficiency
    • Hypermagnesemia
physical exam
Physical Exam
  • Vital signs
    • Unstable?
    • Dysautonomia?
  • Respiratory status
signs of impending nm resp failure
Signs of impending NM resp failure
  • Tachypnea, sinus tachycardia
  • Staccato speech
  • Inability to count to 20
  • Profound weakness of neck flexion
  • Use of accessory muscles (visible, palpable)
  • Orthopnea
  • Paradoxical breathing pattern
  • Signs of bulbar dysfunction (nasal voice, accumulation of saliva, weak cough)
    •  think about aspiration!
physical exam2
Physical Exam
  • Vital signs
      • Note any dysautonomia
  • Presence and pattern muscle weakness
      • Proximal (myopathy), distal (peripheral neuropathy)
      • Symmetric, asymmetric
      • Involvement of cranial muscles
  • Reflexes
  • Sensory changes
  • Dysautonomia
localisation of the disorders
Localisation of the Disorders
  • Clinical picture varies depending on which part of motor unit is involved
regroup
Regroup
  • Is respiratory failure imminent?
  • Should ICU be involved?
  • Where can I localise motor findings?
  • Does it fit with sensory findings?
  • Does it fit with autonomic findings?
  • Does it fit with the history?
  • Can the history help me narrow things down?
laboratory studies
Laboratory Studies
  • CBC
      • Anemia or leukocytosis - systemic disease
      • Eosinophilia - possibly elevated in vasculitic neuropathy, porphyria
  • Lytes, Cr, BUN, Ca, Mg, PO4,
  • Liver enzymes (consider EtOHmyotoxicity)
  • CK (myopathy if very elevated)
  • ESR (infectious or inflammatory disorders)
  • CXR (pneumonia, atelectasis, elevated hemidiaphragm)
  • EKG
    • Changes associated with electrolyte imbalances
    • Arrythmias 2ary to dysautonomia in GBS
    • Axis deviation – may be suggestive of cardiomyopathy
assess respiratory status
Assess Respiratory Status
  • Tests in ER
    • MIP
    • MEP
    • FVC
    • ABG
  • 20/30/40 rule
    • VC: 20 ml/kg
    • MIP: -30cmH20
    • MEP: +40cm H20
myasthenia gravis
Myasthenia Gravis
  • Disorder of transmission across NM junction
  • Auto-immune and congenital form
  • Epidemiology (auto-immune form):
    • 200-400 cases per million population
    • Women > men (3:2)
    • Bimodal incidence
      • F: 20s, 30s; M: 50s, 60s
    • 5-10% co-association with other auto-immune disorders
classification1
Classification
  • Auto-immune – two forms
    • Acquired anti-AChR Abs (85%)
    • Acquired anti-MuSK Abs, a muscle-specific TK
      • 40-50% of anti-AChR seronegative pts
  • Congenital
    • Heterogeneous group (pre or post-synaptic)
    • Of note: do not affect respiratory muscles therefore do not present with myasthenic crisis
clinical features
Clinical Features
  • Painless, fatigable weakness of voluntary muscles
    • Repeated activity  progressive paresis
    • Rest  restoration of strength (at least partial)
  • Usually insidious onset
    • May occur more rapidly after precipitant (stress, infection)
  • Association with thymic abnormalities
    • 10-15% thymoma
    • 50-70% thymic lymphoid hyperplasia
clinical features1
Clinical Features
  • Presenting symptoms:
  • MuSK-MG
    • Younger women
    • Predominantly facial, bulbar and respiratory weakness
    • Relatively mild limb weakness
myasthenic crisis1
Myasthenic Crisis
  • Myasthenic weakness leading to respiratory failure and need for ventilatory assistance
  • Severe weakness of respiratory muscles

and/or

  • Severe weakness of upper airway muscles (bulbar myasthenia)
prevalence and characteristics
Prevalence and Characteristics
  • Life-time prevalence: 20-30%
    • Early onset  younger pt, median onset w/in 8 mos, fast recovery
    • Late onset  older pts, later in dz course, slower recovery
  • White pts respond more poorly than black pts
  • Pregnancy aggravates MG in 30% of women
    • High potential mortality of crisis
precipitants
Precipitants
  • Elements to look for in history/chart:
    • Poor control of generalised disease
    • Medical treatment for bulbar myasthenia
      • Steroids and anti-cholinesterases
    • Use of certain drugs (next slide)
    • Systemic infection, esp. of respiratory tract
    • Aspiration
    • Surgery
    • Others (in refractory myasthenia):
      • Emotional stress
      • Hot environment
      • Hyperthyroidism
drugs1
Drugs
  • Anticholinesterases can also lead to myasthenic crisis
  • Signs of excessive cholinergic activity
    • Miosis, diarrhea, salivation, abdominal cramps, sweating, weakness
investigations
Investigations
  • CBC, extended lytes, BUN, Cr, liver enzymes
  • CXR, U/A +/- blood cultures
  • Obtain VC, MIP, MEP – 20/30/40 rule
investigations1
Investigations
  • Repetitive motor nerve stimulation
    • Stimulate motor nerve at 2-3 Hz and measure CMAP of stimulated muscle
    • Positive if >er 10% decrement in amplitude of CMAP from the 1st to the 5th potential
    • Positive in about 75% of patients withgeneralized MG, if
        • Proximal & clinicallyinvolved muscles are tested
        • Muscle is warm
        • More than one muscle istested
  • Single fibre EMG
  • Tensilon test not recommended in pt suspected of being in crisis
    • False postive, false negative
    • Risk of worsening muscle weakness in pts with anticholinesterase overdose
    • Worsening of bulbar and respiratory symptoms in MuSK-MG
management
Management
  • Monitoring of respiratory status
    • Recognition of impending resp failure
      • Tachypnea, inability to count to 20, saliva pooling, nasal voice, NF weakness, paradoxical breathing
    • Deciding when to intubate
      • (Code status)
      • 20/30/40 rule
      • If in doubt, intubate
      • ?BiPAP
        • Limited experience. May reduce prolonged intubatn and trach
management1
Management
  • General
    • Stop any meds that may be contributing
    • Treat any infection
  • Specific
    • PLEX and IVIG comparable efficacy
      • Based on clinical evidence, few RTCs
      • Earlier response seen with PLEX
        • More likely to extubate at 14 days, better 1-month functional outcome (Qureshi, et al. Neurology, 1999).
management2
Management
  • PLEX
    • Removal of anti AChR and antiMuSK Abs
    • 1 session/day x 5
      • No superiority of PLEX qd x 5 vs qod x 5
    • Rapid onset of action (3-10 days)
    • Need central line with associated complications
      • PTX, hemorrhage, line sepsis
    • Caution in pts with sepsis, hypotension; may lead to increased bleeding and cardiac arrhythmias
management3
Management
  • IVIG
    • 0.4gm/kg/day x 5 days
    • Easilyadministered and widelyavailable
    • Long duration of action
      • May last as long as 30 days
    • Side effects
      • Anaphylaxis in IgA deficiency
      • Renal failure, pulmonary edema
      • Aseptic meningitis
      • Thrombotic complications and stroke
mg overall treatment summary
MG – Overall Treatment Summary
  • 1. Mildweakness: cholinesteraseinhibitors
  • 2. Moderate-markedlocalized or generalizedweakness
    • Cholinesteraseinhibitors, and
    • Thymectomy for patients underage 50-60 yrs
  • 3. Symptomsuncontrolled on cholinesteraseinhibitors
    • Prednisone if severe or urgent
    • Azathioprine
      • Prednisonefailure
      • Excessive prednisoneside-effects
  • 4. Plasma exchange or IV Ig
    • Impendingcrisis; crisis
    • Pre-operativeboost
    • Chronicdiseaserefractory to drugtherapy
  • 5. If abovefails
    • Search for residual thymus tissue
    • Cyclosporine or mycophenylatemofetil

(Sem. Neurol., 2001;21:425-440)

slide39
GBS
  • Most common cause of acute and subacute generalised paralysis
  • Incidence of 0.4 to 1.7/100 000 per yr
  • Worldwide, all ages, both sexes
  • Preceding mild resp or GI infection in 60% (1-3 wks)
    • Campylobacter jejuni (26%),
    • CMV, EBV, VZV
    • Influenza, cocksackie, hepatitis A and B, HIV
  • May also be preceded by:
    • Surgery
    • Immunisations
typical symptoms signs
Typical Symptoms & Signs
  • Sensory
    • Paresthesias and slight numbness distally earliest Sx
    • Reduced proprioception and vibration sense (1 wk)
  • Motor
    • Weakness
      • Evolves symmetrically over days to 1-2 weeks
      • Usually LE before UE, proximal + distal
      • +/- trunk, intercostal, neck, cranial muscles
    • Progresses to total motor paralysis and respiratory failure in 5% of cases
typical symptoms signs1
Typical Symptoms & Signs
  • Reflexes
    • Reduced and then absent
  • Autonomic dysregulation
    • Sinus tachycardia/bradycardia, facial flushing, labile BP, excess or loss of sweating, urinary retention
    • Usually do not persist for >er 1 wk
  • Other
    • Myalgias (50%) in hips, thighs, back
variants
Variants
  • Fisher syndrome
    • Ophthalmoplegia, ataxia, areflexia
    • +/- bilateral facial nerve paresis
    • Associated with anti-GQ1b Ab
  • Acute motor sensory axonal neuropathy (5% of GBS cases)
    • Severe and diffuse axonal damage
    • Abrupt and explosive onset
    • Severe paralysis, minor sensory features
    • Slow and poor recovery
  • Pandysautonomia
    • Severe orthostatic hypotension, anhidrosis, dry eyes and mouth, fixed pupils, arrhythmia, bowel/bladder dysfunction
    • Areflexia without somatic motor/sensory involvement
  • Other variants:
    • Initial cervico-brachial-pharyngeal muscle involvement
    • Generalised ataxia without dysarthria or nystagmus
    • Facial and abducens weakness, distal paresthesias, proximal leg weakness
laboratory findings
Laboratory Findings
  • Most important: CSF, EMG
  • CSF
    • Normal pressure
    • Protein
      • Early (1st 2 days): Usually normal (>85%)
      • Later: High (66% in 1st week, 82% in 2nd week)
      • Amount not correlated with clinical course or prognosis
    • Acellular or few lymphocytes
      • 10% : 10-50 lymphocytes, decreases over 2-3 days; if not: other Dx
    • Oligoclonal bands (10-30%)
laboratory findings1
Laboratory Findings
  • EMG
    • Abnormalities seen within first week of sx
    • Reduction in motor amplitude
    • Slowed conduction velocities
    • Conduction block in motor nerves
    • Prolonged distal latencies (distal conduction block)
    • Prolonged/absent F-responses (involvement of proximal parts of nerves and roots)
laboratory findings2
Laboratory Findings
  • Hematology
    • Abnormal only with infection or other disorder
  • Biochemistry
    • Mild-severe SIADH in 7-26%
  • Liver enzymes
    • Elevated <10% reflecting CMV or EBV infection
  • ESR: Normal unless co-existing process
diagnostic criteria
Diagnostic Criteria
  • National Institute of Neurological Disorders and Stroke (NINDS) criteria are based on expert consensus.
  • Required features include:
    • Progressive weakness of more than one limb, ranging from minimal weakness of the legs to total paralysis of all four limbs, the trunk, bulbar and facial muscles, and external ophthalmoplegia
    • Areflexia. While universal areflexia is typical, distal areflexia with hyporeflexia at the knees and biceps will suffice if other features are consistent.
  • Supportive features include:
    • Progression of symptoms over days to four weeks
    • Relative symmetry
    • Mild sensory symptoms or signs
    • Cranial nerve involvement, especially bilateral facial nerve weakness
    • Recovery starting two to four weeks after progression halts
    • Autonomic dysfunction
    • No fever at the onset
    • Elevated protein in CSF with a cell count <10 mm3
    • Electrodiagnostic abnormalities consistent with GBS
differential diagnosis
Differential Diagnosis
  • Features suggesting another diagnosis:
    • Sensory level, severe bladder or bowel dysfunction  Spinal cord syndrome
    • Marked asymmetry Mononeuritis multiplex/vasculitis
    • CSF pleocytosis Infectious disorders: viral, HIV, lyme, poliomyelitis
    • Very slow nerve conduction velocities, multiple relapses or chronic course -> CIDP
    • Persistent abdominal pain and psychiatric signs  Acute intermittent porphyria
management4
Management
  • General:
    • Recommend admission for observation
      • Can deteriorate rapidly in first days of presentation
      • M&M: Respiratory failure, dysautonomia
      • 25% will require mechanical ventilation
  • Respiratory
    • Measure MIP/MEP/FVC
      • Decision to intubate should be based on downward trend
    • Other measures of respiratory status same
      • Counting to 20, strength of NF
management5
Management
  • Dysautonomia
    • 10% develop hypotension
      • Volume, +/- pressors
    • Hypertension
      • IV labetolol
  • Other complications
    • Adynamicileus
    • PE
    • Aspiration
management6
Management
  • PLEX and IVIG
    • No difference in efficacy between the two
    • Indications for prompt initiation
      • Respiratory failure
      • Bulbar involvement
      • Inability to walk without assistance
      • Usually see these signs day 5-10
      • May occur anywhere from day 1 – week 3
  • Steroids
    • No proven benefit
slide51
PLEX
  • Regimen: 4-6 treatments on alternate days
  • Established usefulness in evolving phase
  • If treated within 2 wks onset
    • Decrease in LOS, ventilation, time to independent ambulation by approx. half
  • Value less clear if started later than 2 wks after initial symptoms
  • Predictors of response
    • Age
    • Preservation of motor CMAP amplitudes pre-PLEX
slide52
IVIG
  • Dose: 0.4 gm/kg/day x 5 consecutive days
  • Cheaper, easier to administer
  • Rare complications
    • Renal failure, proteinuria, pulmonary edema
    • Asceptic meningitis
    • Anaphylaxis in IgA deficiency
course and prognosis
Course and Prognosis
  • Progressive symptoms : 1-4 weeks
  • Plateau: 2-4 weeks
  • Recovery: A few weeks to months
  • Recurrence: 5-10%
  • Mortality
    • 3-5%
    • Cardiac arrest, ARDS, PTX, HemoTX, PE
  • Pronounced disability: 10%
    • Clinical prognostic indicators
      • Greater age
      • Rapid evolution; early and prolonged ventilatory assistance, rapid course
      • Lack of treatment with IVIG or plasma exchange
    • Laboratory
      • EMG: severely reduced CMAP and widespread denervation
pathogenesis
Pathogenesis
  • Most evidence points to cell-mediated immunologic reaction directed at peripheral nerve
    • May be precipitated by antecedent infection
  • Antibodies against myelin components with complement-mediated damage
  • T cells and macrophages become involved in process and lead to destruction of myelin/axon