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: Strokes, ICH, MS
      2. Spinal cord disease: Infection (epidural abscess), ischemia, trauma (transection or impingement/compression syndromes), inflammation (transverse myelitis), tumor.
      3. Peripheral nerve disease: GBS, toxins (ciguatera), tick paralysis, DM neuropathy.
      4. NMJ disease: MG crisis, botulism, organophosphate poisoning, Lambert-Eaton.
      5. Muscle disease: dermatomyositis, polymyositis, alcoholic myopathy, rhabdo.

1. UPPER
   1. Multiple Sclerosis
   2. Poliomyelitis
   3. ALS (upper & lower motor)
2. CORD
   1. Painful
      1. Cord compression
   2. Painless
      1. Transverse Myelitis
      2. Spinal cord infarct
      3. Intramedullary tumor
3. NERVE
   1. Guillian-Barre
   2. Toxic neuropthy (Ciguatera)
   3. Tick paralysis
   4. Diabetic neuropathy
   5. Porphyria
4. MOTOR END PLATE
   1. Myasthenia Gravis
   2. Botulism (descending)
   3. Organophosphate Poisoning
   4. Lambert-Eaton
5. MUSCLE
   1. Painful
      1. Rhabdo
      2. Alcoholic
      3. Myopathy
      4. Polymyositis
      5. Dermatomyositis
      6. Toxins
      7. Hypophos
      8. Hypokalemia - post prandial/ family hx/ thyroid
      9. Polymyalgia rheum
   2. Painless
      1. Familial periodic paralysis
      2. Endocrine
6. MIXED
   1. Upper & Lower Motor Neuron
      1. ALS
   2. Sensory & Motor
      1. Peripheral neuropathy
7. NON-NEUROMUSCULAR
   1. MI
   2. Resp failure
   3. Sepsis
   4. Dehydration
   5. Anxiety
   6. Fibromyalgia/chronic fatigue
   7. 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