What's Lambert-Eaton myasthenic syndrome?
Lambert-Eaton myasthenic syndrome (LEMS) is a rare autoimmune disorder of the neuromuscular junction in which antibodies against presynaptic voltage-gated calcium channels reduce acetylcholine release, producing proximal weakness, reduced reflexes, and autonomic symptoms. About half of cases are paraneoplastic, most often linked to small cell lung cancer. A distinctive feature is that strength and reflexes briefly improve right after exercise (post-exercise facilitation), which separates it from myasthenia gravis.
| Also indexed as | ORPHA:43393, MONDO:0018556 |
|---|---|
| Features mapped | 14 |
| Treatments mapped | 6 |
| Published sources | 9 |
| Last reviewed | 2026-08-04 |
Signs and symptoms
Small cell lung carcinoma
About half of cases are paraneoplastic, meaning they are driven by a hidden cancer, most often small cell lung cancer. Because of this, a diagnosis prompts a careful search for an underlying tumour, often repeated over time.
Anti-P/Q-type VGCC antibody positivity
Most people have antibodies against the P/Q-type voltage-gated calcium channel. These channels normally let the nerve ending release acetylcholine, so blocking them is what weakens the signal to muscle. The antibody test is a key confirming finding.
Calcium channel antibody positivity
Most people with Lambert-Eaton myasthenic syndrome have antibodies against voltage-gated calcium channels (VGCC) on nerve endings, which disrupt the release of the signal that tells muscle to contract. A blood test for these antibodies supports the diagnosis.
Bulbar signs
Bulbar signs — problems with speech and swallowing from weakness of the muscles of the mouth and throat — can occur in Lambert-Eaton myasthenic syndrome, but they tend to appear later in the course and usually in severe, advanced cases rather than at the start.
Diminished deep tendon reflex
Tendon reflexes (such as the knee-jerk) are reduced or absent. A telling feature is that these reflexes can briefly return or strengthen for a few seconds right after the muscle is exercised.
Abnormal autonomic nervous system physiology
Many people with Lambert-Eaton myasthenic syndrome have autonomic nervous system dysfunction, because the same antibodies that weaken muscle also disrupt the nerves controlling automatic body functions. This can cause dry mouth, constipation, blurred vision, reduced sweating, and lightheadedness on standing.
Impotence
Other autonomic symptoms include erectile dysfunction (impotence), changes in sweating, and a drop in blood pressure on standing.
Orthostatic hypotension due to autonomic dysfunction
A drop in blood pressure on standing (orthostatic hypotension) can cause dizziness or faintness, and is part of the autonomic dysfunction seen in Lambert-Eaton myasthenic syndrome.
Constipation
Constipation is one of the autonomic symptoms of Lambert-Eaton myasthenic syndrome, reflecting the antibodies' effect on nerve signaling beyond the muscles.
Abnormality of the orbital region
Eye-related symptoms can occur in Lambert-Eaton myasthenic syndrome, including ptosis (a drooping eyelid) and diplopia (double vision). These ocular symptoms can accompany the leg weakness and autonomic features such as a dry mouth.
Xerostomia
Autonomic nerves are affected too. The most common autonomic symptom is a dry mouth, caused by reduced acetylcholine release at those nerves.
Progressive proximal muscle weakness
The core symptom is gradually worsening weakness in the muscles closest to the trunk, especially the legs, so that walking, climbing stairs, and rising from a chair become difficult.
EMG: repetitive nerve stimulation abnormality
Nerve testing is central to diagnosis. At rest the muscle response is small, but it grows markedly right after brief exercise or with rapid (high-frequency) repetitive nerve stimulation, while slow stimulation shows a decrement. This pattern of post-exercise facilitation is the electrical signature that distinguishes the condition.
Hypohidrosis
Reduced sweating (hypohidrosis) can occur in Lambert-Eaton myasthenic syndrome as part of its autonomic involvement.
How it is diagnosed
Lambert-Eaton myasthenic syndrome
Diagnosed using: Voltage-gated calcium channel antibody testing.
“…antibodies to voltage gated calcium channels are present in the majority of…”
Lambert-Eaton myasthenic syndrome
Diagnosed using: Screening for underlying small-cell lung cancer.
“LEMS is associated with small cell lung cancer (SCLC), or rarely other tumours, in approximately 50 % of cases, for which patients should be carefully…”
Lambert-Eaton myasthenic syndrome
Diagnosed using: Repetitive nerve stimulation.
“Typical electrophysiological findings include small compound muscle action potentials at rest that augment following short exercise, decrement at low…”
Treatment and management
What the research describes, not a recommendation. Treatment decisions belong with your clinician.
This covers treatments that appear in the published research mapped here. Investigational and experimental therapies are not included, so their absence is a boundary of this map, not a sign they do not exist.
amifampridine
Amifampridine (3,4-diaminopyridine) is the first-line symptomatic treatment. It blocks potassium channels in the nerve ending, which prolongs the signal and lets more acetylcholine be released, improving strength.
Used to help with: Lambert-Eaton myasthenic syndrome.
“Amifampridine, a short-acting potassium-channel blocker, is the first-line treatment for Lambert-Eaton myasthenic syndrome.”
pyridostigmine
Pyridostigmine, which slows the breakdown of acetylcholine, can be added to help strengthen the nerve-to-muscle signal, often alongside other treatments.
Used to help with: Lambert-Eaton myasthenic syndrome.
“…combined with pyridostigmine led to marked neurological…”
intravenous immunoglobulin
When symptoms are severe or do not respond to symptomatic drugs, immune treatments such as intravenous immunoglobulin (IVIG) can reduce the harmful antibodies and improve strength. Plasma exchange and immunosuppressants are used similarly.
Used to help with: Lambert-Eaton myasthenic syndrome.
“…four doses of intravenous immunoglobulin…”
prednisone
When Lambert-Eaton myasthenic syndrome is not caused by a tumour, the corticosteroid prednisone — alone or together with other immune-suppressing medicines — is one of the treatment options. It works by calming the immune attack on the nerve ending rather than by easing symptoms directly.
Used to help with: Lambert-Eaton myasthenic syndrome.
“In non-paraneoplastic LEMS, prednisone alone or combined with immunosuppressants are treatment…”
plasma exchange
When weakness is severe, plasma exchange — a procedure that filters the harmful antibodies out of the blood — can give short-term benefit in Lambert-Eaton myasthenic syndrome. It is used much like intravenous immunoglobulin in this situation.
Used to help with: Lambert-Eaton myasthenic syndrome.
“In both MG and LEMS, where weakness is severe, plasma exchange or intravenous immunoglobulin treatment may provide short-term…”
treatment of underlying tumour
When Lambert-Eaton myasthenic syndrome is driven by a hidden cancer (paraneoplastic LEMS), treating that tumour often improves the neurological symptoms. This is why finding and treating an underlying cancer is a central part of care in these cases.
Used to help with: Lambert-Eaton myasthenic syndrome.
“In paraneoplastic LEMS, treatment of the tumor often results in neurological…”
How to read the evidence labels
Where this comes from
This guide is built from 9 published source(s). Every claim above links back to one of them. Click any source ID to read the original on PubMed.
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Printed, source-linked documents built from this condition's graph — ready to bring to an appointment or attach to a coverage request. Every claim carries its published source, the same as this guide.