Lambert-Eaton syndrome

Lambert-Eaton syndrome is an autoimmune disorder characterised by:
  • Muscle weakness which improves on exercise 
  • Hyporeflexia or areflexia 
  • Autonomic dysfunction 

The commonest presenting symptom is leg weakness. Proximal muscles tend to be more affected than distal ones.

It is caused by IgG blocking voltage-gated calcium channels, preventing acetylcholine release.

For around 60% of patients with Lambert-Eaton it is a paraneoplastic syndrome and they have underlying small cell carcinoma of the lung (SCLC). However, the incidence of Lambert-Eaton in those with SCLC is around 3%. Other cancers rarely associated with Lambert-Eaton include breast, colon, bladder, kidney and prostate. It may also be an autoimmune condition with no underlying cancer.

Treatment is with 3,4-diaminopyridine which works by blocking voltage-gated potassium channels.

Since Lambert-Eaton Syndrome can precede presentation of SCLC regular CXR should be undertaken. The risk of developing SCLC becomes negligible 4 years after diagnosis of Lambert-Eaton.

Key points to differentiate between Myasthenia Gravis (MG) and Lambert-Eaton are:
  • Weakness gets worse on exercise with MG but improves with Lambert-Eaton
  • Reflexes are normal in MG but decreased/absent in Lambert-Eaton
  • There are not autonomic features in MG whilst there are in Lambert-Eaton

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