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Information in this website is provided to support your understanding of LEMS but is always secondary to the advice of your doctor. Please consult your doctor for diagnosis or treatment of any medical condition.

History and physical examination

A medical history is taken 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 response to low-frequency nerve stimulation that increases dramatically after exercise or high-frequency stimulation is typically seen in people with LEMS.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

CT scans 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, people with these diseases typically do not show symptoms associated with automatic body functions or decreased reflexes that are common in LEMS. Myasthenia gravis can also be differentiated by the progression of muscle weakness, which usually starts at the head and progresses downwards, whereas the opposite occurs in LEMS. Nerve conduction tests can also help to distinguish between these conditions.1,4

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References:
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 June 2017). 3. Sanders DB. Ann NY Acad Sci 2003;998:500–508. 4. Mareska M and Gutmann L. Semin Neurol 2004;24(2):149–153.