Integrating Discordant Results in CA LEMS Workup: Who Reconciles the Data and Why the Oncologist Must Stay in the Loop

Dr. Sen explains how to manage discordant serologic and electrodiagnostic results without allowing disagreement between tests to paralyze decision-making. If VGCC antibodies are positive but the nerve study is inconclusive, the first step is verifying whether the electrodiagnostic protocol included the post-exercise facilitation and high-frequency repetitive stimulation components required for LEMS detection. Standard neuropathy protocols will not include these, and the referral must explicitly specify LEMS evaluation. A positive VGCC result in the right clinical context may alone be sufficient to proceed with treatment even if electrodiagnostic testing is non-confirmatory. If the antibody is negative but the electrodiagnostic picture is classic for LEMS, the clinical and electrophysiologic picture takes precedence; serologic testing should be broadened with SOX1 and CASPR2, and VGCC testing repeated.

A critical systemic issue is who is responsible for reconciling these results. The oncologist must be looped in from the start. A borderline or positive VGCC result should be treated as a critical lab value requiring proactive outreach from the laboratory, not passive posting in the electronic health record. Assuming someone else is watching results is a common failure point that delays care.

Dr. Primdahl endorses the multidisciplinary approach, emphasizing that close oncology-neurology communication is especially essential when immune checkpoint inhibitor continuation is being evaluated alongside CA LEMS, where monitoring must be concurrent and real-time. She adds single-fiber EMG as an additional confirmatory layer in equivocal cases, given its high sensitivity for neuromuscular junction dysfunction.