The brachial plexus is an anatomical network composed of five spinal nerves. Four of these exit the spinal cord through the cervical spine, which is the area below the skull and above the shoulders, while one exits through the thoracic spine, which supports the upper torso. The nerves of the brachial plexus supply nerve impulses to the shoulder, arm, hand and diaphragm. Injury to the nerves, also called neuropathy, of the brachial plexus can affect any of the structures that this nerve group supplies.
The National Institutes of Health states that brachial plexopathy, or brachial plexus dysfunction, can cause numbness to occur in the shoulder, arm or hand. This can be due to direct injury to the brachial nerves of these areas, stretching injuries, tumors causing pressure on the nerves or damage from radiation therapy.
In severe cases, complete loss of sensation can occur. This condition can result in complications such as recurrent injury to the affected area that goes unnoticed due to diminished pain detection.
Abnormal sensations such as tingling or burning along the areas that are supplied by the nerves of the brachial plexus, primarily the arm and hand, could indicate neuropathy, according to the National Institutes of Health. Paresthesia is a medical term used to denote these sensations, which are sometimes commonly described as a "pins and needles" feeling.
Inadequate nerve supply to the muscles of the arm and hand can result in muscle weakness. The University of Maryland Medical Center lists ways in which brachial plexus neuropathy can manifest as muscle weakness, such as the decreased ability to lift the wrist or extend it backward.
Weakness in the hands is also indicative of brachial plexus neuropathy, though MayoClinic.com notes that, in some cases, the individual may be able to use the fingers but not the arm muscles. In severe or prolonged cases, partial or complete arm paralysis may occur.
The University of Maryland Medical Center lists Horner syndrome among the possible symptoms that can manifest in cases of brachial plexus neuropathy. Horner syndrome is rare. It results from an interruption of the sympathetic nerve signals to the face, and can be caused by injury to the nerves of the brachial plexus. Horner syndrome manifests in symptoms such as constriction of the pupil of the eye, eyelid drooping and lack of sweat on the side of the face that is affected.