Patients with numbness in the left arm and left leg may suffer from stroke, cervical spine and lumbar spine diseases, as follows: 1. Stroke: patients with numbness in the left arm and left leg may be caused by stroke, when there is a stroke in the right cerebral hemisphere, it can cause sensory impairment or decreased muscle strength in the left limb. 2. Cervical spine and lumbar spine diseases: patients with numbness in the left arm and left leg may suffer from cervical spondylosis and lumbar spondylosis with lumbar disc herniation at the same time. Cervical spondylosis can cause numbness and radioactive pain in the left arm, and lumbar disc herniation can cause radioactive pain in the left leg, accompanied by numbness in the leg and foot. For specific differentiation, patients should undergo cranial MRI and CT examination, and cervical MRI and lumbar MRI should be performed to determine the disease through a combination of imaging, physical examination, and questioning of medical history.