Clinical Strategies for Diagnosing CA-LEMS

In this segment, the expert faculty outline a practical and collaborative approach to diagnosing cancer-associated Lambert-Eaton myasthenic syndrome (LEMS), emphasizing the limits of relying solely on serologic tests. The oncologist notes that profound proximal weakness accompanied by a new small cell lung cancer diagnosis typically prompts antibody testing, such as paraneoplastic panels or voltage-gated calcium channel assays. However, the neurologist stresses that these tests lack perfect sensitivity and specificity—up to 15% of patients with LEMS are antibody-negative, while others may have low-titer antibodies unrelated to neurologic disease. As a result, early neurologic evaluation is essential, with diagnosis frequently grounded in a detailed clinical assessment. The faculty describe characteristic features such as proximal-to-distal progression, depressed reflexes that improve with exertion, and late oculobulbar involvement. They highlight the diagnostic role of EMG, particularly post-exertion facilitation, which offers high sensitivity but requires expertise and must be specifically requested. Concurrently, neurologists may initiate cancer screening when patient risk factors signal underlying malignancy.