• Lambert–Eaton myasthenic syndrome (LEMS) is an autoimmune presynaptic neuromuscular junction (NMJ) disorder. It results from antibodies against voltage-gated calcium channels which are involved with acetylcholine (ACh) release.
• The clinical picture is characterized by:
  • Weak proximal limb muscles
  • Depressed tendon reflexes
  • Respiratory failure
  • Abnormal autonomic function such as dry mouth, gastrointestinal slowing, postural hypotension
  • Oropharyngeal and ocular muscles are usually spared.
  • Weakness that improves with sustained contraction
• Approximately one-half of LEMS cases are associated with a malignancy, mainly small-cell lung cancer.

• Cancers: Small-cell lung cancer, as well as non-SCLC, lymphosarcoma, malignant thymoma, cancer of the breast, stomach, colon, or prostate.
• Drugs that may worsen the muscular weakness include aminoglycosides, fluoroquinolones, macrolides, beta blockers, diuretics, procainamide, magnesium salts, calcium channel blockers, intravenous iodinated contrast.

• LEMS is an autoimmune disorder that reduces ACh release from the presynaptic nerve terminals. Antibodies directed against the voltage-gated calcium channel interfere with the release of Ach, resulting in muscle weakness. ACh binding and its effect on the postsynaptic membrane are not impaired, neither is the ACh receptor.
• In patients with cancer, antigens that mimic voltage-gated calcium channels are believed to induce antibodies. In patients without cancer, antibodies to voltage-gated calcium channels are believed to result from an autoimmune state.
• Consequently, muscle weakness improves with use as more Ach becomes available in the NMJ. This phenomenon is referred to as postexercise or postactivation facilitation.

• Assess severity of disease and evaluate pulmonary function.
• Patients show extreme sensitivity to both depolarizing and nondepolarizing blocking drugs and these should be avoided if possible.
• Other non-anesthetic medications may worsen the muscular weakness by inhibiting neuromuscular transmission (see risk factors).
• Postural hypotension may be exacerbated by anesthetic induction agents and mechanical ventilation (MV).
• Whenever possible, the use of ultra-short acting anesthetics should be administered to avoid postoperative respiratory depression and hypoventilation.

Weakness that improves with activity

• 3,4-diamimopyridine increases ACh release
• Guanidine hydrochloride increases ACh release
• Pyridostigmine decreases ACh metabolism and resultantly increases the amount of ACh that is available.
• Immune suppressors (steroids, azathioprine, cyclosporine)
• Plasmapheresis and intravenous immune globulin

• Cancer; see risk factor section
• Other autoimmune disorders:
  • Systemic lupus erythematosus
  • Rheumatoid arthritis
  • Pernicious anemia
  • Thyrotoxicosis

If the patient is poorly controlled, a course of plasmapheresis may be of benefit in the pre-operative period. There should be a 24-hour delay between the last plasmapheresis and surgery in order to restore clotting factors.

• Post-operative care should be done in the ICU with monitoring of respiratory function as well as chest physiotherapy.
• Avoid drugs that may exacerbate motor weakness (see risk factors).

• Aspiration, pneumonia, inadequate cough, atelectasis
• In addition to postoperative pulmonary complications, laryngeal and respiratory muscle weakness may warrant ventilatory assistance in the post-operative period.

• Pulmonary Function Tests
• Functional Residual Capacity
• Myasthenia Gravis

• 358.1 Myasthenic syndromes in diseases classified elsewhere
• 358.30 Lambert-Eaton syndrome, unspecified

• G70.80 Lambert-Eaton syndrome, unspecified
• G73.3 Myasthenic syndromes in other diseases classified elsewhere

Fabrizio Racca , MD

Elena C. Capello , MD

Federica Manfroi , MD

V. Marco Ranieri , MD