Traumatic traction of spinal nerve roots at their origin inside the dura mater.
Predisposing factors General
Lack of leash laws and/or irresponsible pet ownership.
Intact dog.
Bitch in heat.
Environmental
Dog lives on busy road or in city.
Management
Dog allowed to exercise unsupervised.
Old or faulty extending lead.
Dog exercised off the lead.
Pathophysiology
Traumatic.
Limb forcibly abducted or rotated at its attachment to the body traumatic traction on the spinal nerve roots at their origin inside the dura mater disruption of the neural elements interruption of spinal reflexes. Ventral roots are especially susceptible.
Skin desensitization decrease in muscle tone onset of neurogenic muscle atrophy.
Some shrinkage of the areas of skin desensitization as nerves grow in from neighboring innervated areas.
Timecourse (incubation, duration)
Neurological deficits apparent immediately after injury.
Neurogenic muscle atrophy from 7-10 days after injury.
Characteristic 'dropped elbow' with carpal flexion.
Affected limb looks longer than normal limb.
No tricipital, bicipital or pedal reflexes.
Panniculus reflex absent on same side as affected limb.
Consensual panniculus reflex present on the opposite side to the affected limb when the affected side is stimulated.
Muscle atrophy from 10 days after accident, especially in the triceps.
Muscle atrophy eventually involves the whole limb.
Dorsal surface of the paw dragged along the ground severe skin excoriation.
Complete absence of sensation in the distal limb.
55% cases partial Horner's syndrome :
Myosis (small pupil) on same side as affected limb.
Pupil remains reactive to light, dilating in shade and constricting in light.
Slight ptosis (drooping upper eyelid) on the same side as affected limb - lateral and ventrodorsal chest.
Diagnostic investigation Radiography
Lateral and dorsoventral views of humerus and chest - lateral and craniocaudal or caudocranial humerus.
Concurrent orthopedic injuries.
Thoracic radiographs may demonstrate hemothorax, pneumothorax, rib fractures, or pulmonary contusions.
MRI :
To demonstrate nerve root avulsion and/or hematoma.
CT/myelography :
To demonstrate a contrast-outlined diverticulum at the level of the cervicothoracic junction.
Electromyography (EMG) :
To evaluate the degree distribution and severity of neurological damage.
Confirmation of diagnosis Discriminatory diagnostic features
History.
Clinical signs.
Definitive diagnostic features
Neurological examination including assessment of dermatomes of forelimb.
Gross autopsy findings
Avulsion is usually intradural and the lesion in dogs is diffuse rather than circumscribed.
Various branches of the nerve plexus may be swollen and/or hemorrhagic.
Gross displacement/diversion of nerve trunks is sometimes observed.
May see spinal cord hemorrhage.
Histopathology findings
Degenerative changes in dorsal/ventral nerve roots and ventral branches of spinal nerves are characterized by axonal degeneration, myelin fragmentation and loss of myelinated fibers.
Many fibers are damaged where they penetrate the leptomeniges resulting in neuroma formation.
Chromatotolysis cell swelling and neuronal depletion may be seen in ventral nerve cells (seen as 'retrograde' changes).
Differential diagnosis Causes of paralysis of the forelimb
Brachial plexus tumor .
Damage to nerves after they leave brachial plexus.
Hyperextension exercises 4 times a day for 10 min to prevent flexion contracture.
Fluid therapy if animal in shock.
Antibiotic therapy for treatment of any skin wounds.
Non-steroidal anti-inflammatory drugs if pain is present.
Prevention of self-mutilation, eg Elizabethan collar. Note that a properly fitted collar must extend well past the tip of the muzzle when the collar is resting against the shoulders to prevent a dog from reaching the distal limb.
Standard treatment
Amputation of limb if the foot is damaged through dragging on the ground or self-mutilation.
Consider amputation if there is analgesia below the elbow, self-mutilation and no sign of improvement within 4 weeks.
Supportive treatment of local wounds and abrasions.
Prevention of self-mutilation.
Prevention of contractures.
Muscle-tendon transpositions have been successful in some dogs with partial avulsion.
Carpal fusion may be useful in animals with adequate triceps muscle function that have a tendency to knuckle over on their paws.
Monitoring
Neurological examination .
Decrease in size of area of insensate skin.
Improvement in reflexes.
Increase in muscle tone.
Electromyography to monitor improvements in nerve function, and increases in muscle innervation.
Subsequent management
Treatment
Continue physiotherapy to prevent contractures.
Monitoring
Subsequent history and neurological findings.
Neurological re-examination : decreasing area of skin desensitization, improving reflexes, increasing muscle tone.
Very poor; the roots of the radial nerve are commonly injured in brachial plexus avulsion.
An electrodiagnostic evaluation of the radial nerve may provide early prognostic information - prognosis being poor in animals with initial decreased radial nerve conduction velocity. Electrodiagnostic changes will not be reliably present until about 2 weeks after the injury.
If this condition remains unchanged after 4 weeks, there is virtually no chance of spontaneous recovery.
Expected response to treatment
Improvement in muscle tone, reflexes and skin sensitivity can occur over 4-6 months but is uncommon.
Reasons for treatment failure
Lesion too severe.
Client non-compliance with management.
Client refusing to treat on economic or esthetic grounds where amputation is indicated.
Forterre F et al(1998) Myelography by computer tomography for the diagnosis of brachial plexus avulsion in small animals.Tierarzt Praxis26 (5), 322-329 PubMed.
Steinberg H S (1988) Brachial plexus injuries and dysfunctions.Vet Clin North Am18 , 565-580 PubMed.
Wheeler S J et al(1986) The diagnosis of brachial plexus disorders in dogs - a review of twenty-two cases.JSAP27 (3), 147-157.
Bailey C S (1984) Patterns of cutaneous anesthesia associated with brachial plexus avulsions in the dog.JAVMA185 (8), 889-899 PubMed.
Vetstream contributor(s)
Dr Kyle G Braund BVSc MVSc PhD FRCVS DipACVIM , Veterinary Neurological Consulting Services, 1476 Lakeview Ridge, Dadeville, AL 36853, USA.
Mark Rochat DVM MS , Professor and Chief, Small Animal Surgery, Department of Veterinary Clinical Sciences, Center for Veterinary Health Sciences, Oklahoma State University, 01 Farm Road, Stillwater, OK 74078, USA.
traumatic traction on the spinal nerve roots at their origin inside the dura mater 