Lambert-Eaton myasthenic syndrome

Also called LEMS

Weakness that improves briefly with use, the opposite of myasthenia gravis. In half of cases it is the first sign of a lung cancer.

What it is

A rare autoimmune condition in which antibodies block calcium channels at the nerve-muscle junction, reducing the release of the signal that makes muscles contract.

It is distinguished from myasthenia gravis by a characteristic and counter-intuitive feature: **strength briefly improves with repeated effort**, whereas myasthenia gravis gets worse with use. A weak handshake that strengthens after a few seconds of squeezing is the classic bedside sign.

It also differs in distribution: it affects the legs and hips first, causing difficulty rising from a chair and climbing stairs, whereas myasthenia gravis usually starts with the eyes.

**In around half of cases it is a paraneoplastic condition, most often associated with small cell lung cancer**, and the neurological symptoms typically appear months to years before the cancer is detectable. That makes a new diagnosis a reason for CT screening and repeated surveillance, usually for at least two years, which is a critical part of management and is sometimes not arranged.

Autonomic symptoms are common: dry mouth, constipation, erectile difficulty and light-headedness.

Treatment is treating any underlying cancer, plus symptomatic drugs such as amifampridine and immunosuppression.

Signs you might notice

Weakness of the hips and thighs: difficulty rising from a chair, climbing stairs, or walking distances.

Weakness that briefly improves with sustained effort.

Aching in the muscles.

Dry mouth, which is very common and often the first symptom.

Constipation, erectile difficulty, light-headedness on standing.

Drooping eyelids and double vision, usually milder than in myasthenia gravis.

Reduced or absent reflexes that reappear briefly after exercise.

Urgent: difficulty swallowing or breathing, which requires immediate assessment.

Any new diagnosis should prompt urgent CT chest screening for lung cancer, and repeated screening over the following two years even if the first scan is clear.

How it can affect day-to-day life

Delay to diagnosis is typical, often a year or more, and people are frequently told the weakness is deconditioning, fibromyalgia or depression.

The dry mouth is a genuinely useful clue and is dismissed as unrelated.

Because it can precede a cancer by years, the surveillance schedule is one of the most important things to get right, and it is a common gap when care moves between teams.

Certain medicines worsen the transmission problem and should be avoided or used cautiously, including aminoglycoside antibiotics, magnesium and some anaesthetic agents. Anaesthetists must be told before any operation.

Energy management matters; the pattern of temporary improvement with effort can mislead people into overdoing it.

Where a cancer is found, treating it often improves the neurological symptoms substantially.

Supporting someone well

Ask about the pattern: weakness that briefly improves with effort, legs first, plus a dry mouth. That combination points here.

Ask for antibody testing and neurophysiology.

Insist on CT chest screening at diagnosis and repeated surveillance for at least two years.

Tell any anaesthetist before surgery, and check any new medicine against the list to avoid.

Ask about amifampridine, which is the specific symptomatic treatment.

Stop smoking, given the cancer association.

Ask for physiotherapy and energy management rather than being told to exercise more.

Get swallowing or breathing difficulty assessed urgently.

Where to get help

A GP practice for urgent neurology referral; a specialist neuromuscular service for management.

Respiratory or oncology services for cancer screening and treatment.

Myaware support people with Lambert-Eaton as well as myasthenia gravis.

Roy Castle Lung Cancer Foundation where a lung cancer is found.