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Lambert-Eaton Myasthenic Syndrome (LEMS): The Weakness That Can Be the First Sign of Cancer
A rare autoimmune neuromuscular junction disorder causing proximal leg weakness, reduced reflexes, and autonomic symptoms — paraneoplastic in around half of cases, most often with small cell lung cancer. Anti-VGCC antibody testing, repetitive nerve stimulation, and a structured cancer search at KIMS Neuroscience, Hyderabad.
G73.1
>85%
~50–60%
Small Cell Lung Cancer
Lambert-Eaton myasthenic syndrome (LEMS) is a rare autoimmune disorder of the neuromuscular junction in which antibodies against voltage-gated calcium channels (VGCC) on the motor nerve terminal reduce the release of acetylcholine. Unlike myasthenia gravis, where the problem is at the muscle's receptors, the problem in LEMS is on the nerve side of the junction. It produces proximal leg weakness, reduced or absent reflexes that may temporarily improve after brief exercise (post-exercise facilitation — the reverse of MG), and autonomic features such as dry mouth, constipation, and erectile dysfunction. Approximately 50–60% of LEMS cases are paraneoplastic, most commonly associated with small cell lung cancer (SCLC), so every patient requires malignancy screening. The anti-VGCC antibody is positive in more than 85% of cases.
- What it is
- An autoimmune neuromuscular junction disorder in which anti-VGCC antibodies reduce acetylcholine release from the nerve terminal.
- Typical symptoms
- Proximal leg weakness (difficulty rising from a chair or climbing stairs) · Reduced or absent reflexes · Dry mouth · Constipation · Erectile dysfunction · Milder eye and bulbar involvement than in MG.
- The cancer link
- Approximately 50–60% of cases are paraneoplastic — most commonly small cell lung cancer. LEMS can appear before the tumour is detectable, so screening is mandatory and repeated.
- Diagnosis at KIMS
- Anti-VGCC antibody (positive in >85%) · Repetitive nerve stimulation showing an incremental response at high-frequency stimulation · CT chest and structured malignancy screening.
- Treatment
- 3,4-diaminopyridine for symptom management · Immunosuppression for autoimmune LEMS · Treatment of the underlying tumour in paraneoplastic LEMS.
- Contact KIMS
- Outpatient: 040-44885000 · Emergency: 040-46324365 · No referral required.
| Fact | Details |
|---|---|
| Condition | Lambert-Eaton Myasthenic Syndrome (LEMS) |
| ICD-10 | G73.1 |
| Mechanism | Antibodies against presynaptic voltage-gated calcium channels reduce acetylcholine release |
| Key antibody | Anti-VGCC — positive in more than 85% of cases |
| Paraneoplastic association | Approximately 50–60% of cases · Most commonly small cell lung cancer · Malignancy screening including CT chest is mandatory for every patient |
| Distinguishing sign | Post-exercise facilitation — reflexes and strength may briefly improve after exercise, the reverse of myasthenia gravis |
| Electrodiagnosis | Repetitive nerve stimulation shows an incremental response at high-frequency stimulation (MG shows a decrement) |
| Treatment | 3,4-diaminopyridine (symptomatic) · Immunosuppression for autoimmune LEMS · Tumour treatment for paraneoplastic LEMS |
About This Condition
A Junction Disorder With a Different Address
Lambert-Eaton myasthenic syndrome and myasthenia gravis both disrupt the neuromuscular junction, but at opposite sides of it. In MG, antibodies attack the acetylcholine receptors on the muscle. In LEMS, antibodies attack the voltage-gated calcium channels on the nerve terminal — so each nerve impulse releases too little acetylcholine to trigger a full muscle contraction.
That difference produces a characteristic sign. With brief, sustained effort, calcium accumulates in the nerve terminal and acetylcholine release temporarily increases — so strength and reflexes can briefly improve after exercise. This post-exercise facilitation is the reverse of the fatigable pattern of MG, and the same principle underlies the incremental response on high-frequency repetitive nerve stimulation.
The most important fact about LEMS is its association with cancer. Around half of patients have an underlying tumour, most often small cell lung cancer, and the neurological syndrome can appear before the cancer is detectable on imaging. At KIMS, every patient with LEMS undergoes a structured malignancy search, repeated over time when the first screen is negative.
Book a Consultation
Speak directly with our neuromuscular team — anti-VGCC antibody testing, repetitive nerve stimulation, CT chest and structured cancer screening, 3,4-diaminopyridine, and immunosuppression, coordinated with oncology where a tumour is found. No referral required. Monday to Saturday.
040-44885000Emergency line: 040-46324365How Lambert-Eaton Syndrome Presents
Proximal leg weakness
The most common presenting symptom — difficulty rising from a chair, climbing stairs, or walking any distance. Weakness typically starts in the legs and may later involve the arms. Eye and bulbar symptoms occur but are usually milder than in myasthenia gravis.
Reduced or absent reflexes
Deep tendon reflexes are reduced or absent. After a brief period of maximal muscle contraction, reflexes may temporarily return or strengthen — post-exercise facilitation.
Autonomic symptoms
Dry mouth is especially common. Constipation, erectile dysfunction, and reduced sweating reflect the same calcium channel dysfunction in autonomic nerve terminals.
Paraneoplastic LEMS
Approximately 50–60% of cases are associated with cancer, most commonly small cell lung cancer. Risk is higher in smokers and older patients, and in those whose symptoms progress rapidly.
Autoimmune LEMS
In patients without an underlying tumour, LEMS is a primary autoimmune condition, often with a younger age of onset and a slower course, and sometimes with other autoimmune diseases.
The difference from MG
LEMS favours the legs over the eyes, reduces reflexes, causes autonomic symptoms, and improves briefly with exercise. MG favours the eyes and throat, preserves reflexes, and worsens with exercise.
Diagnosis at KIMS
Diagnosis at KIMS
Clinical assessment
Pattern of proximal weakness, reflex testing before and after brief sustained contraction, autonomic symptom review, and smoking and weight-loss history.
Anti-VGCC antibody
The specific marker for LEMS, positive in more than 85% of cases. Tested alongside AChR and MuSK antibodies to separate LEMS from myasthenia gravis.
Repetitive nerve stimulation
A low compound muscle action potential at rest that increases markedly after brief exercise or with high-frequency stimulation — the incremental response that is the electrodiagnostic signature of LEMS.
Malignancy screening
CT chest for every patient, with further imaging such as PET-CT where indicated. When the first screen is negative in a high-risk patient, screening is repeated at intervals, because the tumour may become detectable only later.
Treatment
Treatment of Lambert-Eaton Syndrome
3,4-Diaminopyridine
Prolongs depolarisation of the nerve terminal, increasing calcium entry and acetylcholine release, and improves strength in most patients.
It is the mainstay of symptomatic treatment in both paraneoplastic and autoimmune LEMS.
Treating the Underlying Cancer
In paraneoplastic LEMS, treatment of the tumour — most often small cell lung cancer — is the most important step and can improve the neurological syndrome.
Care is coordinated with the oncology team.
Immunosuppression for Autoimmune LEMS
Corticosteroids and steroid-sparing agents such as azathioprine are used when symptomatic treatment alone is insufficient.
IVIG or plasmapheresis is used for severe weakness or rapid deterioration.
Ongoing Surveillance
Repeated malignancy screening in patients without a tumour at diagnosis.
Regular neuromuscular review to adjust treatment and monitor for respiratory or bulbar involvement.
Related Conditions
Lambert-Eaton syndrome is one of the neuromuscular junction disorders evaluated and managed at KIMS Neuroscience:
FAQs
Frequently Asked Questions
Legs that tire on the stairs. Reflexes that are hard to find. A dry mouth that will not go away. Lambert-Eaton syndrome is rare, treatable — and a reason to look carefully for an underlying cancer.
At KIMS Neuroscience, Secunderabad, Hyderabad, Lambert-Eaton myasthenic syndrome is diagnosed with anti-VGCC antibody testing and repetitive nerve stimulation, followed by CT chest and structured malignancy screening — then treated with 3,4-diaminopyridine, immunosuppression for autoimmune LEMS, and coordinated oncology care for paraneoplastic LEMS. Call 040-44885000. No referral required.
International enquiries: info@kimsneurosciences.com