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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