Synopsis
Distinguish presynaptic Lambert-Eaton weakness from myasthenia gravis and neuropathy, search systematically for small-cell lung cancer, and use symptomatic and immune treatment with appropriate cardiac and seizure precautions.
- Lambert-Eaton myasthenic syndrome is a presynaptic autoimmune junction disorder, usually involving antibodies to P/Q-type voltage-gated calcium channels and reduced acetylcholine release.
- Proximal leg weakness is typical: patients struggle to rise from a low chair, climb stairs or walk uphill before upper limbs become significantly affected.
- Tendon reflexes are reduced or absent but may briefly return after several seconds of maximal muscle contraction, an examination feature called post-exercise facilitation.
Key red flags
Weak swallow, aspiration, falling cough strength or ventilatory symptoms need urgent admission even though severe crisis is relatively unusual.
Investigation priorities
Demonstrate a presynaptic neuromuscular-junction transmission pattern.
Management branches
An adult develops progressive proximal weakness with reduced reflexes.
- Ask about transient exercise improvement, dry mouth, constipation, erectile function, ptosis, dysphagia, smoking and cancer symptoms, then map power and sensation.
- Test reflexes before and immediately after brief maximal contraction, while distinguishing true facilitation from inconsistent technique or patient effort.
Key medicines
AmifampridineThe licensed adult start is 15 mg daily in 3–4 divided doses, increased by 5 mg every 4–5 days to a maximum 60 mg daily; no single dose should exceed 20 mg. In mild renal or hepatic impairment start 5 mg twice daily, and in moderate-to-severe impairment start 5 mg once daily, increasing by 5 mg no more often than every 7 days under the SmPC.
PyridostigmineUse a low oral dose titrated under the BNF and neuromuscular team, usually as adjunct rather than relying on it as the only effective treatment.