Injury to a nerve may arise due to a number of causes. In most acute peripheral nerve injuries, the nerve may be crushed, stretched or severed (cut). Sometimes nerve injury arises secondary to some other pathology related to trauma like compression with swelling of a neighboring organ or structure. Once injured, the nerve may lead to a host of signs and symptoms like pain, abnormal sensations or even a loss of sensation when a sensory nerve is injured. If a motor nerve (responsible for muscle function) is affected, then it can lead to muscle weakness or even paralysis. Identifying the severity of the nerve injury and rapid action may help to restore normal function but this is also dependent on the type of injury.
Diagnosing Nerve Injury
The diagnosis of a nerve injury is based on complete history and physical examination including detailed neurological examination. The clinical evaluation of the patient should be aimed at identifying the site, type and severity of nerve injury. The strength of the muscles supplied by the injured nerve is assessed. The sensory functions of the area innervated by the nerve are examined with tests for touch, pain (pin prick), temperature (heat and cold), vibration, and position.
Nerve supply to the sweat glands is affected immediately following the nerve injury. This can be demonstrated with a ninhydrin test. This is one of the tests that may be performed to confirm the diagnosis of nerve injury.
Nerve Conduction Study
Nerve conduction studies may not be of help immediately after the injury in many patients. These studies are most useful several weeks after the injury. However, nerve conduction studies are important in patients in whom neurological examination is not possible or inconclusive. The neurological evaluation may be a problem in patients with simultaneous injuries to the bones, muscles or ligaments.
Conduction studies can differentiate complete nerve severance (neurotmesis) from blockage of nerve impulses despite an intact nerve (neuropraxia). It also helps in identifying compression injury of nerves resulting from reduced blood supply to nerves. A reduction in nerve conduction by 10% is suggestive of such compression injuries. The regeneration of nerve fibers following nerve repair can also be followed up with nerve conduction studies.
The conduction studies along with the neurological examination should be repeated every 3 to 4 weeks in closed injuries with unknown severity of the nerve injury. It will also help in distinguishing between neuropraxia and axonal injury. A surgical exploration with repair may be done after 3 months if no clinical improvement is noticed.
Damage of bone and other soft tissues sustained during the event that lead to the nerve injury also needs further evaluation. This may require radiological investigations like CT scan or MRI scan. Some of the gross nerve injuries of larger nerves can also be visualized in these radiological studies. MRI scan is also of use in identifying some patients with nerve compression.
Complications of Nerve Injury
Most common complication of nerve injuries are development of chronic neuropathic pain syndromes. It may also be associated with abnormal sensations (paresthesias).
Partial injuries of mixed (motor and sensory) nerves can result in causalgia (severe burning pain). Causalgia develops as a result of scar tissue formation in the regenerating nerve. Patients developing causalgia can have increased pain response to stress, increased sensations (hyperesthesia) and hyper-reactivity to cold or muscular activity.
Paralysis can result from injuries of motor nerves that fail to heal. There may be wasting paralyzed muscle if physical therapy is not provided to the muscles. The muscle wasting can lead to limited mobility of the joint and subsequent joint stiffness.
Prognosis (Outlook) for an Injured Nerve
The prognosis of acute nerve injuries depends on the site, type and severity of the injury. The timing of the surgery is also an important factor. Tension in the sutures of a nerve repair is an important reason for failure of nerve repair surgeries. The length recovery time from nerve injury often affects the patient motivation and compliance to medical advice. Keeping the patient well motivated is therefore also important in the long term prognosis. The recovery of full function of the affected nerve also depends on the treatment and care given to the surrounding tissue injured in the process.