Brachial Plexus Injury
Brachial plexus injuries can cause underarm pain. The brachial plexus is a network of nerves located in the neck and shoulder, which also course through the armpit. This network of nerves can be damaged by pressure, stretching or trauma. Traction of the brachial plexus nerves is one of the most common types of brachial plexus injuries, occurring when the head and neck are forced away from the affected shoulder, toward the opposite side. In severe cases, the nerves may tear away from their roots in the cervical spine or neck. Possible signs and symptoms associated with brachial plexus injuries include underarm pain, numbness and tingling in the arm and reduced motor control of the arm muscles.
Lymphadenitis -- an infection of the lymph nodes or glands -- is a common complication of certain types of bacterial infection. The lymph nodes are small structures that are responsible for filtering toxins out of the body. The lymph nodes contain a substantial amount of white blood cells that help ward off infection. Lymphadenitis manifests when the lymph nodes become enlarged due to inflammation. The inflammation is usually a reaction to invading bacteria, viruses or fungi. Swollen lymph nodes are often located near areas of underlying infection, inflammation or tumors. Lymphadenitis can occur in any lymph node, including the axillary lymph nodes, or the nodes in the armpit. Common signs and symptoms associated with lymphadenitis include swollen, tender and hard lymph nodes and red, tender skin over the affected nodes.
A shoulder dislocation can cause underarm pain. The shoulder is the body's most mobile joint, which makes it prone to dislocations. A shoulder subluxation is a partial dislocation of the shoulder in which the head of the upper arm bone partially slips out of the shoulder socket. A dislocation means that the head of the upper arm bone completely slips out of the shoulder socket. Both conditions cause significant pain and discomfort in the shoulder and underarm. The majority of shoulder dislocations involve a downward and forward slippage of the upper arm bone. Common signs and symptoms associated with shoulder dislocation include swelling, numbness, weakness and bruising in the affected shoulder and underarm.