Entrapment neuropathy is a rather common type of nerve injury in which mechanical factors lead to compression of the nerve and subsequent appearance of pain, paresthesias, and associated muscle abnormalities. Virtually any peripheral nerve can be affected, and the diagnosis should be suspected in all patients who report typical symptoms that suggest a neuronal origin. Imaging studies, in addition to clinical criteria, are used to make the diagnosis.
Entrapment neuropathy is a term describing a type of neuropathy that is rather commonly encountered in clinical practice (carpal tunnel syndrome is one of the examples) and results from either compression, traction or structural impairment of the nerve   . As the nerve becomes compressed or "entrapped" in tissues after trauma or some other form of injury, the blood supply to the nerve is diminished, eventually causing edema, ischemia, necrosis and death of neuronal tissue if the structural deformity is not repaired promptly  . During this process, typical symptoms of neuronal injury arise, such as pain, paresthesia, and numbness . Depending on the affected nerve, both sensory and motor deficits can be observed. For example, deltoid weakness indicates axillary nerve entrapment; restriction of wrist flexion is present in the setting of median nerve compression, whereas loss of sensation in the dorsal proximal areas of the index finger, middle finger and the thumb suggests radial nerve entrapment  . It must be noted that several nerves could be entrapped at more than one anatomical location, which is why recognizing associated signs and symptoms is pivotal for identifying the affected nerve   . The appearance of symptoms can be abrupt or slowly progressive .
A delayed diagnosis of entrapment neuropathy and nerve compression may lead to irreversible neuronal injury and cause a significant impairment in daily life, thus early recognition of this clinical entity is of absolute necessity  . One of the first steps toward the diagnosis is a detailed patient history that will determine the duration of symptoms and their severity, followed by a thorough physical examination, perhaps the pivotal part of the diagnostic workup  . Depending on the cause and location of symptoms, a complete motor evaluation of muscle groups and the sensorium in the areas where the patient reports pain, paresthesias, or numbness, is the mainstay in revealing which nerve is injured  . A presumptive diagnosis might be made solely on clinical findings, but imaging and electrophysiologic studies are highly useful in confirming entrapment neuropathy. Plain radiography, although important in delineating skeletal injuries as potential causes, is of no use in assessing nervous tissues . For this reason, ultrasonography (US) and magnetic resonance imaging (MRI) are recommended but are not equally effective for all anatomical sites    . A hypoechogenic appearance of the nerve, as well as edema, thickening, and fatty atrophy of the muscles supplied by the injured nerve, are frequent findings on US, whereas swelling and hyperintensity are seen on MRI studies   . Conversely, electromyography (EMG) and nerve conduction studies are often used in the setting of peripheral nerve injury and provide important clues in discerning between peripheral and central nerve injuries  .