High resolution of ultrasound is used as an additional diagnostic tool to detect morphological alterations of the peripheral nerves such as increased cross-sectional area. In this immune neuropathy is like chronic inflammatory demyelinating polyneuropathy. The main advantage of nerve ultrasound is that it can be performed quickly, easily and without relevant risks directly by the neurologist.
Nerve ultrasound can help to diagnose inflammatory neuropathies, but may also help in prognosis and follow-up of disease course. For examination of the arm nerves, let the patient sit in a neutral position with the arm resting supinated on a surface such as a leg. Then apply ultrasound gel over the transducer probe wrist, forearm, elbow and upper arm.
To examine the median nerve perform a transverse scan at the wrist level. The median nerve can be easily identified in the carpal tunnel below the transverse carpal ligament next to the tendons of flexor digitorum superficialis and profundus. Then measure the cross-sectional area or CSA of the median nerve at the entrance to the carpal tunnel.
Move the transducer proximally to follow the anatomical course of the median nerve to the forearm and measure the CSA at the forearm. Then follow the anatomical course to the elbow. Move the transducer proximally following the median nerve from the forearm to the elbow and measure the CSA at the elbow.
Then follow the course to the upper arm. Move the transducer proximally following the median nerve from the elbow to the upper arm, and measure the CSA at the upper arm next to the brachial artery. Next, to examine the ulnar nerve, perform a transverse scan at the wrist level.
The ulnar nerve can be identified at the wrist ulnar of the carpal tunnel directly next to the ulnar artery and pisiform bone where it enters Guyon's canal. Measure the CSA of the ulnar nerve at the entrance to Guyon's canal. Move the transducer proximally following the ulnar nerve from the forearm to the sulcus ulnaris at the elbow and then to the upper arm.
After moving the transducer proximally from the wrist to the forearm, measure the CSA at the forearm. Follow the course of the ulnar nerve to the sulcus and measure the CSA at the sulcus ulnaris at the level of the elbow. Follow the anatomical course to the upper arm and measure the CSA.
Next, to examine the radial nerve in the spiral groove, let the patient hold the arm in front of the stomach bent at the elbow. Then scan the radial nerve directly next to the humerus, using the color doppler mode to avoid confusion with the accompanying artery and vein. Color doppler mode shows blood flow in arteria profunda brachii and low flow in the corresponding vein while no flow occurs in the radial nerve.
Additionally, the vein and artery can be compressed by exerting external pressure. Measure the CSA of the radial nerve in the spiral groove. Next to examine the vagal nerve, cervical nerve roots and brachial plexus, apply the ultrasound gel in the middle of the patient's neck.
For the vagal nerve, perform a transverse scan at the middle of the neck and find the carotid artery and jugular vein. The vagal nerve can be found directly next to the carotid artery and jugular vein. Then measure the CSA of the vagal nerve at the carotid sheath at the level of the carotid bifurcation.
Next, to examine the cervical nerve roots, C5, C6, and C7, move the probe dorsal and slide it slightly up and down. The cervical nerve roots appear between the anterior and posterior tubercle of the transverse process. C7 can be recognized by the absence of the anterior tubercle from its transverse process while both anterior and posterior tubercle are found with C5 and C6.Measure the CSA of the nerve roots in the intrascalene space proximal to the formation of the trunk eye in a cross-sectional view.
Next, move the transducer distally following the trunks and plexus to the supraclavicular space. To examine the brachial plexus, follow the anatomical course of the cervical nerve roots distally and then find the trunks and cords of the plexus. Measure the CSA of the plexus at the supraclavicular space.
Alternatively, for evaluation of the nerve roots perform a longitudinal scan to display nerve roots. Measure the diameter of the cervical nerve roots at the most proximal location where the nerve root exits over the transverse process in a longitudinal view. To continue examining the leg nerves let the patient lie down on one side with the leg slightly bent.
Then place some ultrasound gel over the transducer probe, the popliteal fossa, the fibula and the lower leg. To examine the fibular nerve, feel the fibular head and place the transducer directly behind it. Identify the fibular nerve next to the fibular head.
Measure the CSA of the fibular nerve next to the fibular head. Next, move the transducer proximally following the fibular nerve from the fibular head to the fossa poplitea. Then measure the CSA of the fibular nerve in the popliteal fossa.
To examine the tibial nerve in the popliteal fossa find the fibular nerve again and the popliteal artery in the popliteal fossa. In most cases, the tibial nerve can be found just above the popliteal artery. Measure the CSA of the tibial nerve at the popliteal fossa.
To avoid many changes in the patient's position, continue to examine the sural nerve in the same position before continuing with the tibial nerve on the medial malleolus. To examine the sural nerve place the probe at the lateral ankle. In most cases, the sural nerve can be found next to a superficial vein.
Measure the CSA of the sural nerve between the lateral and medial head of the gastric anemia muscle. Finally, to examine the tibial nerve at the ankle let the patient sit or lie on their back with the knees slightly bent. Then place the ultrasound gel at the ankle and the probe directly behind the medial malleolus.
The tibial nerve can be found just next to the posterior tibial artery. Measure the CSA of the tibial nerve at the level of the medial ankle. After performing all measurements on both sides save the results and end the examination.
Reference CSA values for patients studied under this protocol are shown here. Representative images of the six nerve sites used in the adjusted Bochum ultrasound score in a healthy person are shown here. These sites are the median nerve at the forearm and upper arm, the radial nerve at the upper arm, the ulnar nerve at the forearm and at the upper arm and the sural nerve at the calf.
Similar images of a patient with chronic inflammatory demyelinating polyneuropathy are shown here. Each of these six sites is scored with one point if the nerve shows pathological CSA enlargement on one or both sides of the body Immune neurography is another method to detect morphological alterations of the peripheral nerves especially for proximal leg nerves and lumbosacral plexus where nerve ultrasound is difficult to apply. Further research on neuromuscular ultrasound is interesting as the morphological alterations may give insights into pathophysiological aspects like inflammation.
