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Neuromuscular Emergencies Hanni Bouma Objectives Discuss the approach to neuromuscular respiratory failure – – – Signs & Symptoms Differential diagnosis When to intubate Brief overview of GBS & MG Case 1 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 A) 5% B) 10 to 20% C) 25 to 50% D) 70 to 85% Case 2 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 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 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 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? Spinal cord lesion – Motor neuron lesion – GBS, CIDP, critical illness polyneuropathy, Lyme disease, tick paralysis, toxic NMJ disorder – ALS Peripheral nerve lesion – Cervical cord compression, transverse myelitis MG, LEMS, botulism, organophosphate poisoning Muscle lesion – Polymyositis, dermatomyositis, critical illness myopathy, hyperthyroidism, congenital myopathy (muscular dystrophy), mitochrondrial myopathy Mechanisms of NM resp failure 1) Upper airway obstruction: – – 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 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 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 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 HEENT: – – – – 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 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 – Investigations 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 – PFTs may be low if inadequate mouth closure from facial palsy, and may fluctuate in MG Investigations 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 Basic labs (CBC, SMA-10, LFTs, CK) CXR EKG (electrolyte D/O; GBS ass’d w/ dysautonomia arrhythmias) General care 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? – Predictors of need for MV 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: – – – – – – 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 Code status? Identify imminent resp failure early to avoid emergency intubation – – Minimizes atelectasis/pneumonia Minimizes complications of intubation specific to GBS & MG: 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? Few studies on its use in GBS & MG Inappropriate if upper airway function severely impaired or hypercapnic resp failure GBS 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% – – – Campylobacter jejuni (26%) Viral URTI, influenza EBV, CMV, VZV, HIV, hep A & B, coxsackie Other precipitants: immunization, pregnancy, surgery, Hodgkin’s disease Presentation Sensory: – – Motor: – – – – 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: – 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 EMG: – – – – Reduced conduction velocities Loss of F waves Conduction block in motor nerves Reduced motor amplitudes: 2° axonal damage worse Px. CSF: – – High protein (may be normal in first 2 days) No cells or few lymphs 10% have 10-50 lymphs Management Admit for observation (potential for deterioration) Determine if resp failure imminent Dysautonomia: most frequently sustained HTN & tachycardia – – 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): – – – Equally effective PLEX useful in first 2 weeks; benefit less clear after that Steroids no proven benefit Course Progression over 1-4 weeks Plateau: 2-4 months Recovery: few wks to months Mortality 3-5% Poor prognosis: – – – – Resp failure requiring intubation Advanced age Very low distal motor amplitudes (axonal damage) Rapidly progressive weakness over 1 week MG Ab-mediated attack on nicotinic Ach rec defective transmission across NMJ Bimodal: F 20-30 yo; M 50-60 yo 2 autoimmune forms – – 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 Motor: – – – – 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: – – Malignant thymoma in 10-15% (more severe disease) Thymic hyperplasia in 50-70% Myasthenic Crisis Defined by resp failure requiring ventilatory assistance Occurs in 20-30%; mortality 5% Common precipitants: – – – – – – Infection in 40% (esp respiratory) Pregnancy Medications Aspiration Surgery Emotional upset, hot environment Drugs that exacerbate MG Antibiotics: – – – Cardiac: – – – Phenytoin, CBZ Antipsychotics, lithium Thyroid hormones Magnesium toxicity Iodinated contrast agents Muscle relaxants – – All beta-blockers Calcium channel blockers Class I anti-arrhythmics (quinidine, procainamide) Anticonvulsants: – Aminoglycosides (genta, tobra) Fluroquinolones (cipro) Macrolides (erythromycin, azithro, tetracycline, doxycycline) Baclofen Long-acting benzos **Too much anticholinesterase Investigations Ach receptor Abs Anti-MuSK Abs EMG: – Repetitive nerve stimulation: >10% decrement in amplitude betw 1st & 5th CMAP – Single-fiber: “jitter” (variation in time interval betw firing of muscle fibers in same motor unit) 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: – Not recommended in suspected crisis Management Determine if resp failure imminent Stop exacerbating meds Treat infection Symptomatic therapy (mild-moderate weakness): – Short-term disease suppression: – – – – 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: – – – When weakness is inadequately controlled by Mestinon Prednisone Azathioprine (if steroid failure or excessive SE) Key points 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