Lambert-Eaton myasthenic syndrome

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Lambert-Eaton myasthenic syndrome (LEMS) is usually paraneoplastic (P-LEMS) and classically presents as a generalised muscle weakness with diplopia, ptosis, and hyporeflexia. It is due to autoantibodies directed against the presynaptic P/Q-type voltage-gated calcium channels (VGCC), and there is good evidence that different antibodies tend to be involved in the non neoplastic (NP-LEMS) and the paraneoplastic variants[1] . In small cell carcinoma often this is due to anti-glial nuclear antibody against SOX-1[2]. It has also been reported after varenicline and botulinum toxin use.

Contents

Clinical features

  • Proximal muscle weakness
    • Legs more than arms
    • Augmentation of strength during initial voluntary activation
  • Depressed deep tendon reflexes
    • Post-tetanic potentiation
  • Autonomic dysfunction
  • Rarely bulbar or respiratory involvement
  • In 60% underlying malignancy
    • P-LEMS in particular can be associated with cerebellar degeneration

Investigations

  • EMG - small compound muscle action potentials and facilitation with exercise or 20-Hz repetitive stimulation is characteristic compared to the picture in myasthenia gravis.

Treatment

References

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