Hands on Nerve Conduction Studies

Transcription

1 Hands on Nerve Conduction Studies N. CUTANEUS ANTEBRACHII LATERALIS Type of measurement: Antidromic. Position of limb: Subject supine, elbow extended, and forearm supinated. Type of recording electrodes: Surface electrodes on a fixed bar. Placement of recording electrodes: Active electrode over the anterior-radial side of the forearm between the distal and middle third of the forearm, 140 mm distal to the tendon of m.biceps brachii. Reference electrode placed distally. Type of stimulating electrodes: Surface electrodes on a fixed bar. Stimulation point: Elbow, lateral to the tendon of the biceps muscle. Hands on nerve conduction studies Page 1 (9)

2 N. CUTANEUS ANTEBRACHII MEDIALIS Type of measurement: Antidromic. Position of limb: Subject supine, elbow extended, and forearm supinated. Type of recording electrodes: Surface electrodes on a fixed bar. Placement of recording electrodes: Active electrode over the anterior-ulnar side of the forearm at between the distal and middle third of the forearm (140 mm). Reference electrode placed distally. Type of stimulating electrodes: Surface electrodes on a fixed bar. Stimulation site: Over the volar side of the forearm, mm in anterior and lateral to the medial epicondyle. Hands on nerve conduction studies Page 2 (9)

3 Hands on nerve conduction studies Page 3 (9)

4 N. SAPHENUS Type of measurement: Antidromic. Position of limb: Subject supine, knee extended. Type of recording electrodes: Surface electrodes on a fixed bar. Placement of recording electrodes: Over the anterior-medial surface of the distal part of the tibia, 150 mm above the medial malleolus. Reference electrode placed distally. Type of stimulating electrodes: Surface electrodes on a fixed bar. Stimulation sites: Over the medial side of the tibia 140 mm proximal to the recording electrode. (On the medial side of the knee just below the medial epicondyle.) Hands on nerve conduction studies Page 4 (9)

5 N. ulnaris (inching) Position of limb: Patient supine, sitting or reclining. Elbow slightly flexed (15 30 ). The forearm is rotated outwards, the palm faces upwards. The fingers are relaxed in a neutral position, slightly flexed. Type of recording electrodes: Surface plate electrodes. Position of recording electrode: At the midpoint of a line between the fifth metacarpo-phalangeal joint and the priform bone. Position of reference electrode: On the middle phalanx of digit V. Type of stimulating electrodes: Surface electrodes on a fixed bar. Stimulation site: Wrist, 80 mm proximal to the recording electrode. Middle of forearm. Around elbow as described: a line joining the tip of medial epicondyle and the proximal tip of olecranon is drawn and used as reference line. Consecutive stimulation points are marked along the course of the nerve from - 30 mm below epicondyle to +40mm above epicondyle with 10 mm increments. 23 mm - 30 mm + 40 mm Hands on nerve conduction studies Page 5 (9)

6 Inching showing a jump in latency just above epicondylus When you superimpose the signals you can see a slight conduction block as well. Hands on nerve conduction studies Page 6 (9)

7 CMAP from APB with stimulation of median nerve proximal and distal to the carpal tunnel ligament. It is useful to be able to perform a motor stimulation of the median nerve distal to the carpal tunnel ligament (using a stimulation point inside the palm). In this way you can compare the CMAP from wrist stimulation (proximal to carpal tunnel ligament) with palm stimulation (distal to carpal tunnel ligament) and look for conduction block to differentiate whether a low motor amplitude is due to conduction block or axonal degeneration. Hands on nerve conduction studies Page 7 (9)

8 Carpal tunnel diagnosis: motor latency to lumbrical muscles / interosseus muscles. M Lumbricales II Medianus) M Interossu volaris Ulnaris) I M Abductor digiti minimi (n Ulnaris) M Abductor pollicis n Medianus) CMAP from APB }Amplitude CMAP from ADM CMAP from Lumbricalis II CMAP from Interosseus I Latency Due to the anatomy of the intrinsic muscles in the hand you can with one electrode record both from M Lumbricalis II (innervated by median nerve) and M Interosses volaris I (innervated by the ulnar nerve). You can use the same location for the recorded electrode and use the same distance when stimulating the median and ulnar nerves respectively. Thus you can compare the two latencies Hands on nerve conduction studies Page 8 (9)

9 Carpal tunnel tester Method: Measure and mark recording and stimulation points (14 7). Let the hand rest in a relaxed position when you measure on wrist / palm / finger 3. Recording electrodes: surface electrodes Active (black) in palm Reference (red) at wrist (cabel in amplifier 1). Stimulation electrode on finger 3. Cathode on the marked stimulation point and anode distally. Open CT-program in Keypoint Check that you are investigating the correct side. The program will indicate automatically if the patient is not relaxed or if the elctrode impedance is to high. You have to correct that before you can start to stimulate. When "START"-button is green it can be activated by the mouse and the stimulation will start. Stimulation and cursor setting for latencies as well as calculating the index will be automatic. Hands on nerve conduction studies Page 9 (9)