Brachial Plexus Injury and Recovery
Nerve injury can take 3 different forms, from least to most severe:
1) Neurapraxia: transient function loss (ex: conduction block) with no loss of nerve anatomy.
2) Axonotmesis: disruption of axons with some (mild) degree of myelin loss. Importantly the surrounding perineurium and epineurium are intact.
3) Neurotmesis: complete rupture of the nerve (axon, myelin and all surrounding structures).This injury does not lend itself well to recovery.
**Important, but trivial sounding, note: Nerve root avulsion is irreversible.
A recent study evaluated traumatic nerve injury and outlined their findings. The most clinically applicable key points are listed below:
226 animals were included (175 dogs, 51 cats)
46% were injured before age 2
Horner's syndrome was seen in 68 animals (42%of dogs and 38% of cats) with miosis ipsilateral to the affected thoracic limb. Note: It should always be ipsilateral unless there is spinal cord damage.
Cutaneous trunci reflex (which has it's motor origin between C8-T2) was lost in 81% of dogs, again ipsilateral to the affected limb. This reflex doesn't count in cats. :)
Prognostic factors in this study were largely related to electrodiagnostic studies, which are not clinically useful markers in practice. (Unless you have access to electrodiagnostic testing...which I don't, anymore!) That said, we know that animals with neurotmesis do not recover and prior studies have identified that animals with axonotmesis can recover but it may take awhile. Nerves may regrow 1 inch per month for a total of 8 inches. Therefore distal injuries resulting in axonotmesis may result in some functional recovery of the limb.
In the study referenced below, the only important clinical prognostic indicator from this study was the absence of cutaneous trunci reflex. When, absent, it was linked to a lesser chance of recovery, but no statistical analysis was performed to assess this trend. This study also reinforced the finding that electrodiagnostic testing is a valuable testing tool for providing a prognosis for dogs and cats following brachial plexus injury.
Do you have a patient with a traumatic limb injury with possible neurologic involvement? A neurologic examination may be able to better identify chances of recovery and direct treatment towards appropriate physical therapy, acupuncture and other management during the recovery phase. Reach out if I can help!
Have a great week and stay warm in this chilly turn towards fall!
Referenced article: https://doi.org/10.1111/jvim.16254