Breaking Down the Diagnostic Process: How Eaton Syndrome is Identified

The Diagnostic procedure is a difficult and team-based task. It usually takes time to make a diagnosis for health issues.

An outstanding diagnostic framework that delineates the process phases and specifies the kinds of problems that can occur at each one has been released by CRICO Strategies. Our patient partners and research mentors used this approach as they examined their diagnostic breakdowns and journeys.


Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder that makes it difficult to move muscles. It happens when your immune system attacks the area where nerves and muscles connect, called the neuromuscular junction. The damage to this area disrupts how your nerve cells send signals to your muscles, causing weakness. It’s most often seen in people with cancer of the lung, especially small cell lung cancer. It can also be linked to certain cancer treatments, such as chemotherapy and radiation.

The first symptoms of LEMS usually happen in the hip and thigh muscles. These muscle problems can then spread to your arms, shoulders and neck. They can also affect the nerves that connect your face, eyes and ears to your brain (cranial nerves). Symptoms include weakness or loss of movement, tingling sensations, trouble walking and fatigue. People with this condition can have a dry mouth and difficulty swallowing. Symptoms of LEMS improve if the underlying cancer is treated or if you take medicines that suppress your immune system or help strengthen signals between nerves and muscles.

Diagnosis is a complex patient-centered process that involves information gathering and clinical reasoning to determine a person’s health problem. The committee that developed this resource adapted an existing model of diagnostic decision-making to illustrate how the process works. This figure shows that the first step in the diagnosis is collecting information about your symptoms and signs. The next step is organizing and interpreting that information. The final step is forming a working diagnosis.

Physical Examination

Your healthcare provider will look for muscle weakness and other symptoms in a physical examination. These include a weak or numb feeling in your legs, arms, hands, and feet. You may also have a tingling sensation in your fingers or toes, trouble breathing (dyspnea), and a dry mouth (xerostomia). Your healthcare provider will order blood tests to check for antibodies that attack the neuromuscular junction. Your physician will also perform repetitive nerve stimulation to see how well your muscles work. This test can help distinguish LEMS from another condition that affects the nerve-muscle connection, myasthenia gravis.

In people with Lambert Eaton myasthenia syndrome, antibodies destroy the calcium channel at the end of nerve cells. This interferes with the release of acetylcholine, a chemical that transmits messages between nerves and muscles. The antibodies can also reduce the number of signals that reach the brain from the nerve endings, causing fatigue and weakness.

LEMS can be a paraneoplastic disorder associated with cancer, usually small-cell lung cancer. But it can also occur without cancer as part of a general autoimmune state. In either case, the disorder is caused by cancer-related changes that produce abnormal antibodies. The resulting anti-P/Q-type voltage-gated calcium channel antibodies impair neuromuscular transmission by inhibiting inward calcium current and preventing the release of acetylcholine into the synaptic cleft.

Electrodiagnostic Tests

Several disorders affecting nerves or muscles can cause weakness, cramping, stiffness, pain or tingling sensations. Patients with these symptoms often undergo electro diagnostic testing to help determine the diagnosis. These tests read the electrical signals that travel from the brain through motor nerves to the muscles. Two common and valuable tests used to help diagnose Eaton Syndrome are a nerve conduction study and an electromyography needle exam (EMG).

These studies measure how fast or slow a signal is transmitted from a nerve to the muscle. They also measure how much strength the muscle has during a voluntary contraction. These measurements can indicate whether the neuromuscular junction is intact or whether there is a problem with transmission at the neuromuscular junction.

Compared to healthy subjects, patients with LEMS have low compound muscle action potential (CMAP) amplitudes at rest. They also show a decremental response to low rates of repetitive nerve stimulation and an incremental response after high-rate stimulation. These findings are consistent with the underlying defect of the neuromuscular junction described by Lambert and Eaton in 1950 and ’60, now known as Lambert-Eaton myasthenic syndrome.

MU Health Care doctors who perform electrodiagnostic testing have undergone extensive training in performing and interpreting these tests. They must pass an American Board of Medical Specialties certification examination in Neuromuscular Medicine and are certified by the American Board of Electrodiagnostic Medicine.

Genetic Testing

A genetic test can tell whether a person has a certain gene change known to cause disease. Genetic counseling is usually part of the process of getting a genetic test. It helps a person understand the test results and what they mean for their health and well-being.

There are many kinds of genetic testing. Some large-scale tests look for many gene changes simultaneously (genome or exome sequencing). These tests can detect very rare genetic conditions. They can also identify whether a person carries a gene variant that increases their risk for a disease like cancer.

The genetic test most often used to diagnose Eaton Syndrome is an electrophysiology study called repetitive nerve stimulation. It involves sending small electrical impulses to the muscles and measuring how quickly an electric current passes through them. These tests can confirm a person has LEMS and help determine its severity.

Genetic testing is only recommended for some. It can be hard to interpret the results, and people may have unneeded anxiety or false reassurance. There’s also a chance that the test will find no genetic change or a gene variation that doesn’t increase a person’s cancer risk (a variant of uncertain significance, or VUS). If this happens, people need guidance about preventive care and screening from a knowledgeable healthcare provider.

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