False-negative transcranial motor evoked potentials and transient supplementary motor area syndrome during falx meningioma surgery: a case report

Transcranial electrical stimulation motor evoked potentials (TES-MEPs) are widely used to predict postoperative motor deficits during brain tumor surgery but may not reflect dysfunction in higher-order motor networks. We describe a 65-year-old woman with a right falx meningioma who developed transient supplementary motor area (SMA) syndrome despite preserved TES-MEP signals. Gross total resection was performed with TES-MEP and somatosensory evoked potential monitoring. Throughout resection, TES-MEP amplitudes remained stable without significant reduction. However, immediately after surgery the patient showed left lower-limb weakness, while postoperative MRI showed no infarction or hematoma. The neurological deficit resolved within 24 hours, and such a short recovery course may also fall within the clinical spectrum of supplementary motor area syndrome. This case demonstrates that transient motor deficits consistent with supplementary motor area syndrome may occur after falx-adjacent meningioma surgery despite preserved TES-MEP signals. It highlights the need to interpret TES-MEP findings in the context of tumor location.