Sudden bulging of arm veins may be caused by certain diseases, such as upper extremity deep vein thrombosis, superior vena cava syndrome, varicose veins, etc., which should be promptly consulted to find out the cause. 1. Upper extremity deep vein thrombosis: due to the change of body position or strong activity of the upper extremity, resulting in vascular compression, or venous cannulation, venography, etc. may lead to the formation of deep vein thrombosis of the upper extremity. Symptoms such as bulging of superficial veins in the arm, accompanied by swelling of the upper extremity, pain, skin bruising, etc. may occur. 2. Superior vena cava syndrome: It refers to complete or incomplete obstruction of the reflux of the main branches of the superior vena cava, elevated venous pressure, or with the formation of collateral circulation caused by various reasons, which is generally manifested by the formation of thrombus in the vein and filling and expansion of the veins to the subcutaneous veins, and the symptom of sudden bulging of the veins of the arm may appear. 3. Varicose veins: the veins appear to be bulging, dilated, tortuous and other manifestations, mostly due to congenital structural defects of the venous wall, venous return obstacles and other factors. Varicose veins of the upper limbs can be characterized by local hyperpigmentation, edema and bulging veins. Sudden bulging of the arm veins should be promptly consulted to identify the cause of the disease, and appropriate treatment should be carried out if necessary.