Weakness

Background

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

Clincial Features

History

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

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 - +/-

Differential Diagnosis

Weakness

• Neuromuscular weakness
  • Upper motor neuron:
    • CVA
    • Hemorrhagic stroke
    • Multiple sclerosis
    • Amyotrophic Lateral Sclerosis (ALS) (upper and lower motor neuron)
  • Lower motor neuron:
    • Spinal and bulbar muscular atrophy (Kennedy's syndrome)
  • Spinal cord disease:
    • Infection (Epidural abscess)
    • Infarction/ischemia
    • Trauma (Spinal Cord Syndromes)
    • Inflammation (Transverse Myelitis)
      • Acute flaccid myelitis
    • Degenerative (Spinal muscular atrophy)
    • Tumor
  • Peripheral nerve disease:
    • Guillain-Barre syndrome
    • Toxins (Ciguatera)
    • Tick paralysis
    • Diabetic peripheral neuropathy
  • Neuromuscular junction disease:
    • Myasthenia gravis crisis
    • Botulism
    • Organophosphate toxicity
    • Lambert-Eaton myasthenic syndrome
  • Muscle disease:
    • Rhabdomyolysis
    • Dermatomyositis
    • Polymyositis
    • Alcoholic myopathy
• Non-neuromuscular weakness
  • Can't miss diagnoses:
    • ACS
    • Arrhythmia/Syncope
    • Severe infection/Sepsis
    • Hypoglycemia
    • Periodic paralysis (electrolyte disturbance, K, Mg, Ca)
      • Hypokalemic periodic paralysis
      • Thyrotoxic periodic paralysis
    • Respiratory failure
  • Emergent Diagnoses:
    • Symptomatic Anemia
    • Severe dehydration
    • Hypothyroidism
    • Polypharmacy
    • Malignancy
    • Aortic disease - occlusion, stenosis, dissection
  • Other causes of weakness and paralysis
    • Acute intermittent porphyria (ascending weakness)

Diagnosis

Workup

On all pts:

• CBC (anemia)
• Chem 10 (electrolyte disturbance,hypoglycemia, uremia)
• ECG (Ischemia,hypo/hyperkalemia)

Consider:

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

Treatment

Intubation Indications

• Severe fatigue
• Inability protect airway
• Rapidly increasing PaCO2
• Hypoxemia despite O2
• FVC <12 mL/kg
• Neg Insp Force <20 cm H2O