Amyotrophic lateral sclerosis

Background

• Progressive muscle atrophy/weakness due to degeneration of upper and lower motor neurons
• Patients will rarely present to the ED undiagnosed
• Likely related to mutated superoxide dismutase (SOD1) gene
• Involvement of the anterior horn cells

Clinical Features

A man with ALS using a head-mounted laser pointer to comunicate. Note asymetic motor weakness.

• Acute respiratory failure
  • Predicted by forced VC <25 mL/kg or 50% decrease from normal
• Aspiration pneumonia
• Trauma related to extremity weakness
• Asymmetric weakness without sensory findings with mixed upper and lower motor nerve findings

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)

Evaluation

MRI (axial FLAIR) demonstrates increased T2 signal within the posterior part of the internal capsule, consistent with the diagnosis of ALS.

Evaluate for complications of ALS or other treatable causes of progressive weakness

Labs

• CBC
  • Evaluate for anemia/infection
• CPK
  • Elevation associated with myopathy
• BMP
  • Electrolyte abnormalities (hypercalcemia, hypokalemia, etc.) can cause weakness
• UA
  • Evaluate for source of infection
• ABG
  • Helps identify respiratory failure

Imaging

• CXR
  • May identify aspiration, pneumonia, or other comorbid conditions

Other

• FVC
  • Sensitive indicator of respiratory muscle weakness
  • FVC <50% typically requires ventilatory support

Management

• Nebulized medications
• Steroids
• Antibiotics for infectious complications
• Assisted ventilation / intubation if in respiratory failure and aligned with goals of care

See Also

• Weakness
• Intubation

References

• Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 7e (2010), Chapter 167. Chronic Neurologic Disorders