Antidromic vs orthodromic sensory median nerve conduction studies

Abstract

Objective: Median sensory nerve conduction studies are arguably the most often performed electrodiagnostic tests worldwide. Routine tests in clinical practice are done using either antidromic or orthodromic techniques type of stimulation, with no universal agreement on the use of one or the other technique.

Methods: We review the advantages and drawbacks of antidromic and orthodromic as well as their particularities for clinical application and research.

Results: The two techniques differ on how physical and physiological changes affect the action potential. Near-nerve recording is better suited for the orthodromic than for the antidromic technique, while studies of nerve excitability are better suited for the antidromic than for the orthodromic technique.

Conclusion: Both techniques are equally suitable for routine tests but research studies may specifically demand one or the other.

Keywords: Antidromic nerve conduction test; Carpal tunnel syndrome; Orthodromic nerve conduction test; Sensory nerve action potential.

Fig. 1

Recordings of antidromic (A and B) and orthodromic (C and D) sensory nerve action potentials of the 3rd finger, at progressively increasing stimulus intensity. Antidromic testing with stimulation at the wrist over the median nerve and recording with ring electrodes on the 3rd finger. Orthodromic testing with stimulation at the finger with ring electrodes and recording at the wrist. Distance between stimulating cathode and active recording electrodes: 14 cm. Inter-electrode distance for stimulation and recording with both techniques: 3 cm. At each graph, the top traces are recorded at threshold intensity for eliciting a recognizable action potential and the bottom traces are those corresponding to a supramaximal stimulus intensity.

Fig. 2

Traces reproduced from the articles published by Bannister and Sears (1962) and Murai and Sanderson (1975) showing antidromic action potentials. See the absence of the approaching phase.

Fig. 3

Orthodromic (top) and antidromic (bottom) action potentials obtained in the segment wrist to 3rd finger in a patient with severe chemotherapy-related sensory neuropathy. Observe the absence of any recognizable action potential in the top trace (orthodromic) and the preservation of a low amplitude long latency response in the bottom trace (antidromic).

Fig. 4

Differences between double peak potentials of different origin. The traces of the left show the anAP and caAP recorded at the wrist with orthodromic stimulation of the thumb in a healthy subject. The traces in the right show the double peak potential recorded at the wrist to orthodromic simultaneous stimulation of the superficial radial nerve and the median nerve at the thumb in a patient with carpal tunnel syndrome. Note the difference in behavior of the second action potential with increasing the stimulus intensity, disappearing when it is the expression of an anAP and maintaining the amplitude when it is the expression of a delayed median nerve.