Transient Upper Limb Weakness Following Ultrasound-Guided PECS II Block: A Case Suggestive of Long Thoracic Nerve Involvement

The pectoral nerve (PECS) II block is widely used for perioperative analgesia in breast surgery. We describe a case of transient upper limb weakness following a PECS II block performed in the infraclavicular area without accompanying sensory deficits. A 61-year-old woman underwent left reduction mammoplasty under general anesthesia. A left-sided ultrasound-guided PECS II block using 30 mL of 0.25% ropivacaine was performed. Postoperatively, she reported difficulty elevating her left arm above shoulder level, while elbow flexion, hand grip strength, and sensory function remained intact. The symptoms resolved spontaneously by the following day without intervention. This presentation suggests selective motor involvement, most likely affecting the long thoracic nerve. A two-site approach combining PECS I block and serratus anterior plane block may be considered as a potential alternative to reduce unintended motor effects, although further investigation is required.