Dr Shah on Current Guidelines for Diagnosing Cancer-Associated LEMS

"The biggest things [to keep in mind when diagnosing LEMS] are recognizing the proximal weakness and the autonomic dysfunction from a diagnostic perspective.”

Shailee S. Shah, MD, a clinical assistant professor of neurology (MS/neuroimmunology) at Northwestern University Feinberg School of Medicine, expands on the most important factors to consider when diagnosing cancer-associated Lambert-Eaton myasthenic syndrome (LEMS), as per the updated National Comprehensive Cancer Network (NCCN) Clinical Practice Guidelines in Small Cell Lung Cancer (SCLC).

In August 2025, the NCCN updated its guidelines for the treatment of patients with SCLC to include new information on how to diagnose LEMS and a revision of symptom specificity. LEMS is specifically defined by the presence of proximal muscle weakness and autonomic dysfunction. Shah emphasized that recognizing these two key symptoms is one of the biggest initial steps in the diagnostic process.

The updated guidelines recommend that diagnosis should involve a neurological evaluation, ideally in consultation with a neurologist. Diagnostic testing may include specific auto-antibody testing for LEMS, particularly the PQ-type calcium channel antibodies. Although N-type voltage-gated calcium channel antibodies may also be tested, Shah noted that they may be less specific. The presence of specific antibodies can therefore be an indicator of LEMS, but careful interpretation is necessary when relying on those tests in isolation, Shah emphasized.

Finally, the guidelines also recommend the use of amifampridine as a potential treatment option in consultation with a neurologist. Engaging a neurologist is also recommended if there is high suspicion of LEMS, and electrodiagnostic studies, such as a nerve conduction study, should be considered, Shah advised.