The myth of the supplementary motor area syndrome: the etiology of motor deficits after dorsomedial frontal resections.

Objective

Resections of the supplementary motor area (SMA) in the dorsomedial frontal cortex (DMFC) have traditionally been thought to result in predictable postoperative motor deficits termed the "SMA syndrome." However, the true incidence, etiology, and duration of these deficits seem overstated in the modern era. Herein, the authors aimed to critically evaluate and reassess the SMA syndrome in the context of surgical navigation, retractorless surgery, and contemporary motor mapping and monitoring techniques.

Methods

The authors retrospectively reviewed the electronic medical records of all patients who underwent DMFC resections for tumors or epilepsy between 2004 and 2025 at a single institution. Patients with insufficient data were excluded from the study. Compiled data included demographics, presenting symptoms, surgical characteristics, intraoperative mapping, postoperative motor function, postoperative complications, and follow-up visits up to 12 weeks.

Results

Eighty patients were eligible for study inclusion. New postoperative motor deficits occurred in 33.8% of patients (27/80); however, when cases with concomitant involvement of the primary motor cortex or cingulate gyrus were excluded, the incidence of SMA-specific deficits was only 10.0% (8/80). Moreover, 81.5% of new deficits (22/27) resolved by a median of 13 days, and 51.9% (14/27) recovered very rapidly. Patients with new deficits were more likely to have right hemisphere resections (p = 0.033). Motor strip involvement (p = 0.019) and postoperative complications (p = 0.042) were also associated with new deficits. No association was found with the use of intraoperative mapping, percentage of resected SMA, or other clinical characteristics. As expected, patients with new deficits experienced a longer postoperative hospital course (p = 0.023) and were more often discharged to inpatient rehabilitation (p = 0.012). Permanent deficits occurred in 6.3% of patients (5/80) and were more often associated with preoperative weakness (p = 0.047) and a major postoperative complication (p = 0.013).

Conclusions

These findings challenge the classic perspectives on SMA syndrome. When resections are confined to the SMA, postoperative deficits are uncommon, mild, and resolved rapidly. Persistent deficits reflect injury to adjacent eloquent regions rather than injury from the SMA resection itself. With gravity-based retraction, modern navigation, and functional mapping, DMFC lesions can be resected more safely than in the past. Study findings support redefining SMA syndrome and expanding the role of mapping-guided resections in this region.