The course of the disease
A phlebitis of the arm is usually not dangerous. Especially an inflammation of the superficial veins is usually a spatially limited inflammatory reaction that can be treated quickly. Once the symptoms have subsided, no further complications are to be expected.
In the case of a vein thrombosis of the arm, however, there is a risk of pulmonary embolism. The thrombus (blood clot) can be transported by the bloodstream from the arm vein to the heart and from there to the lungs. There the thrombus can block the blood vessels, which can lead to a life-threatening situation.
The thrombosis
Basically, there is a risk of thrombosis in the case of an inflammation of the arm veins. However, this is very rare compared to leg vein thrombosis. One speaks of a thrombosis when a blood clot blocks a blood vessel.
A thrombus can occur for a number of reasons. These causes can be, for example, a coagulation disorder, a slowed blood flow or bacterial inflammation. If the thrombus blocks a blood vessel, a local reaction such as swelling and pressure pain occurs.
A particular danger of thrombosis is that the thrombus can become loose and be transported further with the blood flow. If it enters a pulmonary vessel and blocks it, a pulmonary embolism may occur. Pulmonary embolism is a life-threatening situation and must be treated as soon as possible, otherwise the lung tissue can die.