Lambert-Eaton myasthenic syndrome

Background
  • Disease of the neuromuscular junction leading to primary presentation of weakness
  • Caused by auto-antibodies against the voltage-gated calcium channels at the NMJ

Epidemiology
  • Predominantly a disease associated with older men with history of cigarette smoking and lung cancer
    • 50% of patients have concurrent small-cell lung cancer
  • Syndrome can precede detection of malignancy by several years
  • Paraneoplastic syndrome in 60-70% of cases

Clinical Features
  • Often presents with alteration in gait or difficulty rising from a chair
  • Fluctuating symmetric weakness and fatigue, especially of proximal leg muscles
  • Improvement in strength with sustained or repeated exercise (in contrast to MG)
    • Lambert sign: handshake strength increases over several seconds
  • Myalgias
  • Muscle stiffness (especially in hip and shoulders)
  • Paresthesias
  • Metallic taste
  • Eye movements are unaffected
  • Sensory examination normal
  • Autonomic dysfunction (dry mouth, erectile dysfunction)
  • Compared with myasthenia gravis, LEMS begins with lower extremities weakness and rarely begins with extraocular muscle weakness
  • Respiratory failure can occur in late stages of the disease
  • Paraneoplastic and autoimmune form of LEMS have similar signs and symptoms

Differential Diagnosis

Weakness

Evaluation
  • Diagnosis is generally a clinical diagnosis
  • Confirmation testing for VGCC antibodies
  • Neurophysiologic testing

Management

Disposition
  • Admission required when infectious complications occur or when severe disability requires inpatient immunotherapy
  • Referral to rheumatology
  • Any patients with risk factors for small cell lung cancer will need to be referred for evaluation of underlying malignancy

See Also

References
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