Total lesion of the radial nerve in the arm with preservation of the superficial radial nerve sensory action potential

Lesão total do nervo radial no braço com preservação do potencial sensitivo do nervo radial superficial

LETTERS

Total lesion of the radial nerve in the arm with preservation of the superficial radial nerve sensory action potential

Lesão total do nervo radial no braço com preservação do potencial sensitivo do nervo radial superficial

Eduardo Rodrigues Davidovich; Marcelo Ribeiro Caetano; Osvaldo J. M. Nascimento

Neurology and Neuroscience Clinical Research Sub-Unit (Neuro-UPC), Hospital Universitário Antonio Pedro, Universidade Federal Fluminense (UFF), Rio de Janeiro RJ, Brazil

^{Correspondence}

The electrodiagnostic test (EDX) interpretation of focal peripheral nerve lesions is based on detailed knowledge of nerve and muscle anatomies.

The occurrence of anatomical variations can result in the misinterpretation of EDX analysis leading to diagnostic error. The aim of this report was to call attention for an anatomical variation in which the lateral antebrachial cutaneous nerve (LACN) innervates the radial border of the dorsum of the hand, in addition to or replacing the superficial radial nerve (SRN). From an anatomic point of view, this anatomic variation is well-described. On the other hand, there is no neurophysiological technique able to confirm or deny its occurrence.

CASE REPORT

A 54-year-old woman was referred to the Neurology Department - Antonio Pedro University Hospital for an EDX evaluation of a possible left radial nerve lesion. She underwent elective surgery to remove a lipoma in her left arm, 30 days before the consultation. She had no complaints regarding the peripheral nervous system prior to surgery. At the immediate postoperative period, she was unable to extend her wrist and left hand fingers, which is compatible with radial nerve injury. Numbness was not present in the dorsum of left hand. This clinical picture remained unchanged until the neurophysiological consultation. Physical examination revealed extension paralysis of the left wrist and fingers. Left arm extension strength was normal.

EDX showed a normal sensorial nerve conduction in the SRN (first finger and in the dorsum of the hand), median, and ulnar nerves of both hands. The motor nerve conduction was not present in the left radial nerve and was normal in the right, median, and ulnar nerves (Table). The needle electromyography showed positive sharp waves, fibrillations, and absence of functioning motor units in muscles innervated by the left radial nerve, with the exception of the triceps.

DISCUSSION

Appleton¹, in 1911, reported the first description of this anatomical variation based on a forearm dissection. He found only the posterior radial nerve interosseous branch with absent SRN, below the elbow. On the dorsum of the hand, the LACN extended out beyond its usual distribution to supply the SRN territory (Figure). The dorsal branch of the ulnar nerve had greater ramifications than those usually observed by completing the innervation of the dorsal hand. Other authors^2-5 have studied the distribution of LACN and SRN in the dorsum of the hand and confirmed the existence of this anatomical variation.

In our assessment, the occurrence of an anatomical variation involving LACN and SRN, in which the cutaneous territory of the SRN is wholly or partially supplied by the LACN, can explain the data obtained in the presence of total lesion of the radial nerve in the arm. In cases of proximal radial nerve injury, the occurrence of this variation may lead to diagnostic errors in the EDX study, in which a total axonal damage may erroneously be considered as partial lesion with a conduction block component.

Conflict of interest:

There is no conflict of interest to declare.

Received 27 March 2012

Received in final form 19 June 2012

Accepted 26 June 2012

• 1. Appleton AB. A case of abnormal distribution of the n. musculocutaneous, with complete absence of the ramus cutaneous n. radialis. J Anat Physiol 1911;46:89-94.
• 2. Stopford JSB. The variation in distribution of the cutaneous nerves of the hand and digits. J Anat 1918;53:14-25.
• 3. Mackinnon SE, Dellon AL. The overlap pattern of the lateral antebrachial cutaneous nerve and the superficial branch of the radial nerve. J Hand Surg 1985;10:522-526.
• 4. Huanmanop T, Agthong S, Luengchawapong K, et al. Anatomic characteristics and surgical implications of the superficial radial nerve. J Med Assoc Thai 2007;90:1423-1429.
• 5. Yogesh A, Marathe R, Pandit S. Musculocutaneous nerve substituting for the distal part of radial nerve: a case report and its embryological basis. J Neurosci Rural Pract 2011;2:74-76.

Publication Dates

• Publication in this collection
  16 Jan 2013
• Date of issue
  Jan 2013