The authors report a case of man-in-the-barrel (MIB) syndrome occurring after an extensive revision involving thoracoilium instrumentation and fusion for iatrogenic and degenerative scoliosis, progressive kyphosis, and sagittal imbalance. Isolated brachial diplegia is a rare neurological finding often attributed to cerebral ischemia. It has not been previously reported in patients undergoing complex spine surgery. This 70-year-old woman, who had previously undergone T11-S1 fusion for lumbar stenosis and scoliosis, presented with increased difficulty walking and with back pain. She had junctional kyphosis and L5-S1 pseudarthrosis and required revision fusion extending from T-3 to the ilium. In the early postoperative period, she experienced a 30-minute episode of substantial hypotension. She developed delirium and isolated brachial diplegia, consistent with MIB syndrome. Multiple studies were performed to assess the origin of this brachial diplegia. There was no definitive radiological evidence of any causative lesion. After a few days, her cognitive function returned to normal and she regained the ability to move her arms. After several weeks of rehabilitation, she recovered completely. Man-in-the-barrel syndrome is a rare neurological entity. It can result from various mechanisms but most commonly seems to be related to ischemia and is potentially reversible.