Final answer:
Muscle rigidity is an early sign of malignant hyperthermia, in addition to an increased temperature.
Step-by-step explanation:
The early sign of malignant hyperthermia, in addition to an increased temperature, is muscle rigidity. Malignant hyperthermia is a rare, life-threatening condition that can be triggered by certain medications used during general anesthesia. It causes a rapid rise in body temperature, muscle rigidity, and other symptoms. It is important to recognize and treat this condition promptly to prevent complications.