The possible causes of pain in the left arm and leg include poor posture, trauma, cervical and lumbar diseases, and cerebral infarction. 1. Poor posture: it may be due to poor sitting or sleeping posture, causing the left arm and left leg to be pressurized, and the symptoms of pain and numbness appear. 2. Trauma: when the left arm and left leg are traumatized at the same time, the soft tissue injury, fracture, dislocation and other conditions caused by the left arm and left leg can also cause pain in the left arm and left leg. 3. Cervical spine disease: It may be due to cervical spondylosis or cervical disc herniation, etc., which presses the local nerve root and causes pain and numbness in the left arm. 4. Cerebral infarction: If the patient suffers from cerebral infarction, it may cause the symptoms of left arm and left leg pain at the same time. Left arm and left leg pain may also have other reasons, it is recommended to go to the regular hospital in time to improve the relevant examination, after clarifying the cause of the disease, under the guidance of the doctor to carry out targeted treatment or therapy.