Equis ISSN 2398-2977

Median - ulnar nerve: paralysis

Contributor(s): Frank Andrews, Caroline Hahn, Graham Munroe, Vetstream Ltd

Introduction

  • Cause: singular or combined paralysis is uncommon. Brachial plexus injuries and spinal cord lesions involving the brachial intumescence may affect these nerves along with other nerves. External trauma directly or indirectly (via upper forelimb fractures) to these nerves individually or together is a very uncommon cause.
  • Signs: goose-stepping gait, hyperextension of the carpus, the fetlock and the pastern, dragging of the toe.
  • Diagnosis: clinical signs, neurological examination and electrodiagnostics.
  • Treatment: DMSO, corticosteroids, physiotherapy, rest.
  • Prognosis: fair to good depending which nerve(s) are affected.
  • Resulting syndromes are not well documented.

Pathogenesis

Etiology

  • An isolated paralysis of the median ulnar and/or ulnar nerves is a rare condition and it is slightly more common alongside other nerve dysfunction, including the musculocutaneous.
  • Brachial plexus injuries and spinal cord lesions involving the gray matter of the brachial intumescence may affect these nerves.
  • External trauma directly or indirectly (via upper forelimb fractures, especially of the elbow) to these nerves individually or collectively does occur, but is not common.

Pathophysiology

  • The nerves are well protected under the shoulder girdle and not often involved in long-bone fractures, though elbow fractures may affect the ulnar and median nerves.
  • Paralysis of these nerves rarely occurs individually and usually they are affected together. Paralysis of these nerves can be associated with dysfunction of other peripheral nerves such as the musculocutaneous.
  • The median and ulnar nerves supply the muscles flexing the carpus and digits. Section of the proximal part of the median nerve experimentally resulted in decreased carpal and fetlock flexion and subsequent toe-dragging. Partial sensory loss occurred in the skin over the medial pastern region. Transection of the ulnar nerve proximally lead to similar gait changes as in the median nerve, but to a slightly more obvious degree. There was decreased sensation in the lateral aspect of the cannon and caudal forearm.

Timecourse

  • Experimental studies showed that the gait deficits may disappear within 2 or 3 months due to compensation and adaptation, although if the ulnar nerve is involved, they may continue for longer with persistent stumbling on the leg and decreased fetlock flexion.

Diagnosis

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Treatment

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references fromPubMedandVetMedResource.
  • Hahn C (2008)Common peripheral nerve disorders in the horse.In Pract30(6), 322-326VetMedResource.
  • Alexander K & Dobson H (2003)Ultrasonography of peripheral nerves in the normal adult horse.Vet Radiol Ultrasound44(4), 456-464PubMed.
  • Blythe L L & Kitchell R L (1982)Electrophysiologic studies of the thoracic limb of the horse.Am J Vet Res43(9), 1511-1524PubMed.

Other sources of information

  • Mayhew I G (2009)Large Animal Neurology.2nd ed. Wiley-Blackwell, Oxford, UK. pp 309.
  • Blythe L L (1997)Peripheral neuropathy.In:Current Therapy in Equine Medicine. 4th edn. Ed: Robinson N E. Saunders, Philadelphia, USA. pp 314-318. 


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