Weakness

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Approach

Determine if pt has actual neuromuscular weakness (suggesting CNS dysfuction) or non-neuromuscular weakness.

DDX

  1. Neuromuscular weakness involves derangement of CNS (UMN), PNS (LMN), the motor endplate, or the muscle:
    1. Can't miss dx:
      1. UMN:
        1. CVA
        2. Intracerebral Hemorrhage (ICH)
        3. Multiple Sclerosis
        4. ALS (UMN & LMN)
      2. Spinal cord disease:
        1. Infection (Epidural Abscess (Spinal))
        2. Infarction/ischemia
        3. Trauma (Spinal Cord Syndromes)
        4. Inflammation (Transverse Myelitis)
        5. Tumor
      3. Peripheral nerve disease:
        1. Guillain-Barre Syndrome
        2. Toxins (Ciguatera)
        3. Tick Paralysis
        4. DM neuropathy (non-emergent)
      4. NMJ disease:
        1. Myasthenia Gravis crisis
        2. Botulism
        3. Organophosphate Toxicity
        4. Lambert-Eaton Myasthenic Syndrome
      5. Muscle disease:
        1. Rhabdomyolysis
        2. Dermatomyositis
        3. Polymyositis
        4. Alcoholic myopathy
  1. Non-neuromuscular weakness can be infectious, cardiovascular, metabolic, toxicologic:
    1. Can't miss dx:
      1. ACS/MI
      2. Arrhythmia/Syncope
      3. severe infection/Sepsis
      4. Hypoglycemia
      5. Periodic paralysis (electrolyte disturbance, K, Mg, Ca)
      6. Respiratory failure
    2. Emergent Dx:
      1. Symptomatic Anemia
      2. Severe dehydration
      3. Hypothyroidism
      4. Polypharmacy
      5. Malignancy

Workup

On all pts:

  1. CBC (anemia)
  2. Chem 10 (electrolyte disturbance,hypoglycemia, uremia)
  3. ECG (Ischemia,hypo/hyperkalemia)

Consider:

  1. CK (mypoathies)
  2. ESR
  3. CXR and UA (pt w/infectious sx and elderly)
  4. FVC (if e/o resp compromise, i.e. Myasthenia, GBS)
  5. CT head (if focal findings, AMS, h/o cancer, h/o any trauma in pt on anticoagulation)
  6. LP (CNS infection, GBS)

HPI

  1. True motor weakness (neuromuscular weakness)? Bilateral or unilateral (distribution of weakness)?
    1. Bilateral weakness:
      1. W/symmetric ascending paralysis? GBS
      2. W/weakness involving both CN + PNS? Inflammatory/Autoimmune or toxic/metabolic
      3. W/discrete sensory level and/or bladder dysfxn? Spinal cord lesion
      4. W/involvement of proximal > distal musculature? Myopathy
    2. Unilateral weakness: CVA, TIA
  2. If non-neuromuscular weakness then BROAD Ddx obtain:
    1. ECG, CBC, Chem10, LFTs, blood cx, UA/UCx, drug levels, CXR, Consider Head CT (focal deficit, AMS, h/o CA, anticoagulation w/minor trauma)
  3. Onset of weakness sudden or gradual?
    1. Sudden suggests vaso-occlusive etiology CVA/TIA
    2. Gradual onset likely non-vascular
  4. Significant event surrounding onset of weakness?
    1. SZ prior to weakness? Todd’s paralysis
    2. Migraine HA? Complicated migraine
    3. Sudden onset of severe HA? SAH
    4. Trauma? Epidural or SDH
    5. Severe migratory neck or chest pain? Arterial dissection syndromes
  5. Temporal pattern to weakness? Fluctuating or fixed weakness?
    1. Weakness w/repetitive motions? NMJ pathology like MG
  6. Associated Sx?
    1. HA: SAH, epidural/SDH, complicated migraines (young females), not usually stroke/TIA (unless high ICP)
    2. Vision changes: Posterior circulation stroke, MG
    3. SOB: CV etiology
    4. CP or neck pain: Acute arterial dissection, AMI
    5. Abdominal or back pain:
      1. w/alteration of bowel habits? Botulism, organophosphate poisoning, toxins, GBS, electrolyte imbalance.
      2. w/LE weakness? AAA with spinal cord infarction
      3. Back pain with unilateral weakness? Herniated disk w/nerve impingement
      4. BLE weakness w/sensory level s/p trauma? SCI, cauda equina syndrome
    6. N/V: sign of ↑ ICP, can lead to electrolyte imbalances
    7. Rash: Dermatomyositis

Physical Exam

Focus on clarifying if pt has true loss of strength and determining distribution of deficits. Check for trauma, carotid bruits, thyroid enlargement, irregular rhythm, unequal pulses, rashes or ticks.

Neuro Exam Findings

Upper Motor Neuron

  • BRAIN
    • Weakness - variable
    • Bowel/Bladder - 
    • Reflexes - increased
    • Sens - diminished
    • Pain - no
    • Asymmetric/unilateral
  • BRAINSTEM
    •  "crossed" findings - ipsilateral cranial nerve weakness and contralateral hemiparesis 
  • CORD
    • Weakness - fixed level
    • Bowel/Bladder - YES
    • Reflexes - increased
    • Sens - diminished
    • Pain - +/-

Lower Motor Neuron

  • NERVE
    • Weakness - distal > proximal and ascends
    • Bowel/Bladder - NO
    • Reflexes - diminished
    • Sens - nl/paresthesias
    • Pain - no

End-Plate/Muscle

  • MOTOR END PLATE
    • Weakness - occular,bulbar and descends, fatigable
    • Bowel/Bladder - NO
    • Reflexes - nl/diminished
    • Sens - nl
    • Pain - no
  • MUSCLE
    • Weakness - proximal > distal
    • Bowel/Bladder - NO
    • Reflexes - nl/diminished
    • Sens - nl
    • Pain - +/-

Intubation Indications

  1. Severe fatigue
  2. Inability protect airway
  3. Rapidly increasing PaCO2
  4. Hypoxemia despite O2
  5. FVC <12 mL/kg
  6. Neg Insp Force <20 cm H2O

Source

8/15/13 adapted from Rosen, Tintinalli, Intro to Clincal EM, Lampe, Birnbaumer, Donaldson