Numerous conditions can cause underarm or armpit pain. According to MedlinePlus, the armpit, also known as the axilla, is a common location for lymph node enlargement. Other structures in or around the armpit--such as nerves, muscles, bones and blood vessels--can cause underarm pain or discomfort. Underarm pain may be caused by traumatic injury, nervous system disorders or certain medical conditions. Some types of underarm pain require medical intervention to help resolve the underlying cause of the symptoms.
Brachial Plexus Injury
Brachial plexus injuries can cause underarm pain. According to the American Association for Surgery of the Hand, the brachial plexus is a network of nerves located in the neck and shoulder region. These nerves course through the axilla, or armpit, on their way toward the upper extremity. Brachial plexus injuries occur when this network of nerves is damaged by pressure, stretching or cutting. 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 shoulder. 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
MedlinePlus states that lymphadenitis is an infection of the lymph nodes or glands. Lymphadenitis is a common complication of certain types of bacterial infection. The lymph nodes are small structures that are responsible for filtering lymphatic fluid. 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. According to MedlinePlus, common signs and symptoms associated with lymphadenitis include swollen, tender and hard lymph nodes and red, tender skin over the affected nodes.
Shoulder Dislocation
A shoulder dislocation can cause underarm pain. According to the American Academy of Orthopaedic Surgeons, or AAOS, the shoulder or glenohumeral joint is one of the body's most mobile joints, which makes the shoulder prone to dislocations. Shoulder subluxations and dislocations are separate conditions. A shoulder subluxation is a partial dislocation of the shoulder in which the head of the humerus, or arm bone, partially slips out of the glenoid labrum, or shoulder socket. A dislocation means that the head of the humerus 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 head of the humerus. Common signs and symptoms associated with shoulder dislocation include swelling, numbness, weakness and bruising in the affected shoulder and underarm. The AAOS notes that some shoulder dislocations also involve ligament, tendon and nerve damage.
