What is the most common cause of primary upper extremity DVT?

The most common cause of primary upper extremity deep vein thrombosis (DVT) is associated with congenital conditions, specifically a congenital cervical rib. This anatomical variation can lead to an abnormality in the thoracic outlet, which can compress the veins and thereby facilitate thrombosis. The presence of a cervical rib can reduce the space available for venous outflow, particularly when combined with certain arm positions or repetitive motions, making it a significant risk factor for developing upper extremity DVT.

In contrast, while trauma, prolonged sitting, and lymphatic obstruction may contribute to DVTs in general, they are not the primary causes of upper extremity DVT. Trauma usually pertains to acute injuries that may lead to secondary DVT rather than being a primary cause. Prolonged sitting is commonly associated with lower extremity DVTs, especially in those undergoing long flights or sedentary occupations. Lymphatic obstruction, while it can complicate conditions related to venous circulation, does not typically play a central role in the development of primary upper extremity DVT.