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Educational draft · awaiting clinical reviewUse Rapid for revision, not patient-care decisions. Check current national and local guidance and the BNF or BNFC before acting.

Lambert-Eaton myasthenic syndrome

Neurology · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

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Escalate

Severe dysphagia, aspiration, respiratory weakness or rapid generalised decline requires urgent admission, although respiratory crisis is less common than in myasthenia gravis. New haemoptysis, superior vena cava obstruction, severe hyponatraemia or other cancer complications also need expedited investigation. Amifampridine overdose or interaction can provoke seizure and cardiac rhythm disturbance.

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.
  • Autonomic symptoms such as dry mouth, constipation, erectile dysfunction, blurred vision and orthostatic light-headedness are common and diagnostically useful.
  • Strength may transiently improve with exertion before later fatigue, contrasting with the more consistent use-dependent worsening of myasthenia gravis.
  • Ocular and bulbar symptoms can occur but are often milder or later than in acetylcholine-receptor myasthenia; prominent early ptosis does not by itself exclude Lambert-Eaton disease.
  • A substantial proportion of cases are paraneoplastic, most importantly with small-cell lung cancer; age, smoking and rapid evolution increase that probability.
  • Low-frequency repetitive nerve stimulation shows a small compound muscle action potential, while high-frequency stimulation or brief exercise produces a marked increment.
  • Amifampridine is first-line symptomatic treatment where licensed and commissioned, but dose limits, seizure risk, QT assessment and interacting medicines require specialist prescribing.
  • Treating an underlying cancer may improve neurological disease; non-tumour or persistent cases may need pyridostigmine, immunoglobulin or immunosuppression through a neuromuscular team.

Key red flags

Bulbar or respiratory decline

Weak swallow, aspiration, falling cough strength or ventilatory symptoms need urgent admission even though severe crisis is relatively unusual.

Investigation priorities

01
Repetitive nerve stimulationFirst step

Demonstrate a presynaptic neuromuscular-junction transmission pattern.

Management branches

LocalisationIdentify presynaptic junction failure

An adult develops progressive proximal weakness with reduced reflexes.

  1. Ask about transient exercise improvement, dry mouth, constipation, erectile function, ptosis, dysphagia, smoking and cancer symptoms, then map power and sensation.
  2. Test reflexes before and immediately after brief maximal contraction, while distinguishing true facilitation from inconsistent technique or patient effort.
  3. Refer to a neuromuscular service for repetitive stimulation and calcium-channel antibodies, avoiding a diagnostic trial of high-risk medicine without confirmation.

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.Contraindicated with epilepsy, uncontrolled asthma and specified QT-prolonging or narrow-therapeutic-window combinations; review ECG, electrolytes, paraesthesia and abdominal effects. NHS access and funding vary, and NHS England does not routinely commission amifampridine phosphate outside its stated policy route.
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.Diarrhoea, cramp, salivation and bradycardia limit dosing; renal impairment and concurrent conduction disease require particular care.
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Sources and review status6 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • Association of British Neurologists guideline resourcesUK specialist assessment and management of neuromuscular-junction disorders.
  • FIRDAPSE summary of product characteristicsLicensed amifampridine dosing, contraindications, interactions and monitoring.
  • BNF amifampridine monographUK prescribing and safety information for symptomatic treatment.
  • NICE lung cancer assessment guidanceImaging, referral and multidisciplinary assessment when small-cell cancer is suspected.
  • NHS England specialised neurology commissioning policiesCurrent England commissioning position for amifampridine in Lambert-Eaton myasthenic syndrome.
  • NHS England immunoglobulin commissioning criteriaCurrent acute Lambert-Eaton immunoglobulin indication, initial dose and conditional second dose.

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateRapid draftClinical stateAwaiting reviewJurisdictionUnited Kingdom