Page 293 - Canine Lameness

16.3 ­Neurorogico giNciNi AANicgio ctNe trucigi gim 265

In general, the prognosis for brachial plexus injury is fair to be guarded. Nociception is the most
important prognostic factor and, if absent, is associated with poor prognosis for recovery. The suc-
cess of nerve regeneration is largely determined by the degree of disruption of the neuronal ele-
ments. Nerve injury can be classified into three broad categories, from least to most severe:
neuropraxia, axonotmesis, and neurotmesis (Welch 1996). Neuropraxia is a transient nerve dys-
function (physiologic conduction block) with little to no structural damage. It may be due to tran-
sient ischemia or mild demyelination but typically resolves over one to two months. Sensation is
often persevered because large diameter sensory axons are often spared. Axonotmesis is disruption
of axons but the nerve sheath remains intact. Both motor and sensory deficits are common along
with typical LMN signs. Spontaneous recovery occurs, although not as rapidly as neuropraxia.
Lastly, neurotmesis is complete disruption and/or separation of the nerve (i.e. avulsion). Complete
paralysis of the denervated muscle and absent nociception is expected. Spontaneous recovery only
occurs rarely.
Treatment for brachial plexus injury most commonly consists of conservative treatment with a
focus on rigorous physical therapy and general supportive care to prevent complications such as
self-mutilation due to abnormal sensation, excoriation of the digits, neurotrophic ulcers, and mus-
cle contracture.

16.3.2.2.2 Radial Nerve Injury Traumatic injury to the radial nerve is usually associated with
first rib fractures causing proximal nerve injury or humeral fractures affecting the distal
portion. Clinically, the elbow is dropped and the animal walks with the carpus and digits
knuckled. If the nerve branches supplying the triceps muscle are not involved, elbow extensor
function may be preserved. Clinical history (of trauma) usually aids in establishing the
diagnosis. Appropriate therapy of the orthopedic injuries is essential. Treatment of the
neurological injury is typically conservative as described for brachial plexus injury. Similarly,
the prognosis varies depending on the severity of neuronal injury. Neuropraxia is more
common in cases of radial nerve injury; thus, most animals recover in one to two months.
Cutaneous sensation, including nociception, is the most significantly guiding factor where
loss of sensation carries a poor prognosis.

16.3.2.3 Neuritis
Brachial plexus neuritis is a rare multiple mononeuropathy, meaning multiple nerves within the
same limb are affected. This distinguishes this relatively focal disease from more generalized dys-
function of multiple nerves on different limbs and/or cranial nerves called polyneuropathies (e.g.
idiopathic polyradiculoneuritis). The disease can be unilateral or bilateral but if it is bilateral,
signs are usually asymmetric; less severe forms have been reported with a shifting leg lameness.
The pathogenesis is unknown but, given the similarities to a disease described in humans called
serum neuritis, a hypersensitivity reaction to an immunogen (e.g. rabies vaccine and feeding
horse meat) leading to axon and myelin loss has been proposed (Dewey and Talarico 2016). A
tentative diagnosis can be made based on history, especially if there is exposure to a possible
immunogen, and clinical findings of acute unilateral or bilateral LMN paresis or plegia.
Neuroimaging such as CT or MRI may show nerve pathology (e.g. enlargement, increased signal
intensity, and contrast enhancement). Electrodiagnostic testing and muscle and/or nerve biopsies
would support, and possibly confirm, the diagnosis further. With only a few reported cases, little
is known about the prognosis, but recovery appears to be very protracted (Steinberg 1988;
Summers et al. 1995). There is no specific treatment for this disorder, although glucocorticoid
therapy has been used.