**2. Etiology**

There are many different situations that may be a direct cause of nerve compression. Ana‐ tomically, nerves can be compressed when traversing fibro-osseous tunnels, passing between muscle layers, through traction as they cross joints or buckling during certain movements of the wrist and elbow. Other causes include trauma, direct pressure and space-occupying lesions at any level in the upper extremity.

There are other situations that are not a direct cause of nerve compression, but may increase the risk and may predispose the nerve to be compressed specially when the soft tissues are swollen like synovitis, pregnancy, hypothyroidism, diabetes or alcoholism [1].

Physicians in touch with patients who suffer from upper extremity compression neuropa‐ thies must apply all of their skills to correctly distinguish symptomatic nerve entrapment form other neurologic entities such as myelopathy, braquial plexopathy, radiculopathy, and other central nervous system disorders, that can mimic peripheral nerve entrapment.

Besides these pathologies, the differential diagnosis must include painful rheumatologic and orthopedic disorders; and other psychological entities, such as somatoform and factitious disorders.

present, accompanying symptoms, and if they have improved with time or with a particular

Compression Neuropathies http://dx.doi.org/10.5772/55316 105

Besides a complete history of our patient, a thorough nerve exam needs to be addressed based on the knowledge of the upper extremity nerves anatomy in order to determine the possible site of compression. Our physical exam must include a sensitive and a motor evaluation of the complete upper extremity, beginning with the evaluation of specific movements of the shoulder, arm, forearm, elbow, wrist and digits to determine which muscles are affected and the range of motion of each of these muscles. Next, the sensitivity must be tested, light touch, pain, pressure, vibration and two-point discrimination among the specific distribution of the main nerve involved. There are some complementary tests we may apply in order to guide our exam according to the nerve we think is involved. These specific tests will be discussed

Electrophysiologic testing is part of the evaluation, but it never substitutes a complete history and a thorough physical examination. These tests can detect physiologic abnormalities in the course of motor and sensory axons. There are two main electrophysiologic tests: needle electromyography and nerve conduction, which permit differentiating between a focal mononeuropathy, a radiculopathy, and a plexopathy, or the discovery of a more diffuse

The electromyography detects the voluntary or spontaneous generated electrical activity. The registry of this activity is made through the needle insertion, at rest and during muscular activity to assess duration, amplitude, configuration and recruitment after injury. Recruitment will be affected if demyelination occurs, but will not result in abnormal spontaneous activity. Meanwhile, axonal injury will result in both recruitment and abnormal spontaneous activity, which will not be seen on needle electromyography until

Nerve conduction assesses for both sensory and motor nerves. This study consists in applying a voltage simulator to the skin over different points of the nerve in order to record the muscular action potential, analyzing the amplitude, duration, area, latency and conduction velocity. The amplitude indicates the number of available nerve fibers. Some authors consider diminished amplitude below 50% to be suggestive of compression. In such cases, we will find a normal response to distal stimulation but no response proximal to the site of entrapment. If the compression progresses, our results will be compatible with axonal degeneration with diminished amplitude of the response with relative preservation of the conduction velocity

process, such as a systemic peripheral neuropathy or motor neuron disorder.

and distal latency until the remaining axons are completely damaged [5].

action taken by the patient.

further in the chapter [3].

**5. Electrophysiology**

2 weeks after the initial insult [4].

**4.2. Physical exam**
