Weakness

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: CVA, Intracerebral Hemorrhage (ICH), Multiple Sclerosis, ALS (UMN & LMN).
      2. Spinal cord disease: Infection (Epidural Abscess (Spinal)), infarction/ischemia, trauma (Spinal Cord Syndromes), inflammation (Transverse Myelitis), tumor.
      3. Peripheral nerve disease: Guillain-Barre Syndrome, toxins (Ciguatera), Tick Paralysis, DM neuropathy.
      4. NMJ disease: Myasthenia Gravis crisis, Botulism, Organophosphate Toxicity, Lambert-Eaton Myasthenic Syndrome.
      5. Muscle disease: dermatomyositis, polymyositis, alcoholic myopathy, Rhabdomyolysis.

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)

Diagnosis

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 - +/-

Emergent Threat/ED Workup

1. CORD
   1. paralysis
   2. MRI, neurologist
   3. consdier steroids in high suspicion
2. NERVE
   1. resp failure
   2. FEV1, airway mgt, ticks?, neurologist
3. MOTOR END PLATE
   1. resp failure
   2. FEV1, airway mgt, Tensilon Test?
4. MUSCLE
   1. Rhabdo
   2. urine myoglobin, serum CK, BUN/Cr
   3. serum K+

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

2/26/06 DONALDSON (adapted from Rosen, Lampe, Birnbaumer)

adapted from Hockberger