History and physical examination
Review of medical history is done to look for risk factors for cancer (e.g. smoking) and other autoimmune diseases.2 Other key diagnostic features are the presence of common LEMS symptoms such as muscle weakness, dry mouth and decreased reflexes.1 Because LEMS is often caused by cancer, the doctor will also check for the presence of an underlying cancer.2
Nerve tests
Nerve tests assess how well nerve signals reach the muscles. Nerve conduction studies and low-frequency repetitive nerve stimulation are usually the first tests to be carried out.2 A decreased muscle response to low-frequency nerve stimulation or increased muscle response/strength after a brief muscle exercise is typically seen in LEMS patients.1–3
Blood tests
Blood tests will be performed to check for antibodies against voltage–gated calcium channels, which are found in the majority of people with LEMS.1,2 Additional tests may be carried out to distinguish cancer-associated LEMS from non-cancer-associated LEMS.2
Scans
Computed tomography scans (also known as CT-scan) are used to look for any cancers that might be causing LEMS. As small-cell lung cancer is the most common cancer associated with LEMS, a chest CT scan will be performed. If the chest CT scan is negative, follow-up CT scans or other imaging tests may be carried out.2
Differential diagnosis
Several other conditions can cause similar symptoms to LEMS, such as muscle weakness. The most common are myasthenia gravis and myopathy; however, typical signs in LEMS include decreased or absent reflexes and impaired function of the autonomic nervous system.2 Myasthenia gravis can also be differentiated by the progression of muscle weakness, which usually starts at the head and progresses downwards, whereas in LEMS weakness usually spreads downwards from your hips and thighs to your feet, and upwards towards your head. Nerve conduction tests can also help to distinguish between these conditions.1,4
1. Titulaer MJ, Lang B, Verschuuren JJGM. Lancet Neurol 2011;10:1098–1107. 2. BMJ Best Practice. Lambert-Eaton myasthenic syndrome; diagnostic approach. Available at: http://bestpractice.bmj.com /best-practice/monograph/1052/diagnosis/step-by-step.html (accessed April 2021). 3. Sanders DB. Ann NY Acad Sci 2003;998:500–508. 4. Mareska M and Gutmann L. Semin Neurol 2004;24(2):149–153.