Dogs and cats commonly present for brachial plexus injury, usually after a trauma, but what about sciatic nerve injury? The sciatic nerve is composed of the peroneal and tibial nerves and makes up a lot of the L6-S3 nerve roots. It's a big one! So, how easy is it to damage all or part of this workhorse? Damage can take on 3 forms. First, and most severe, is neurotmesis which means transection of axion and myelin and perineural tissues. Second, is axonotmesis, which suggests damage to the axon with preservation of the myelin and perineural structures. Finally, and least concerning, is neurapraxia, which results in functional damage but minimal to no structural damage. Neurapraxia could be like a "stretch" or loss of minimal myelin. A recent study, published by Dell'Apa, et al from Italy, outlined the signs, etiology and prognosis for 38 dogs and 10 cats diagnosed with a sciatic nerve injury.
What are common clinical signs of sciatic nerve injury?
According to their study, Dell'Apa et al found that the majority of dogs (~80%) had either a loss of hock flexion, or a lack of hock extension. Along with this, about 75% of dogs had a loss of proprioception in the affected limb. There was variable sensory loss (deep pain) and about 13% of dogs had evidence of a root signature. All cats demonstrated a loss of hock extension (i.e. showed dropped hock) and 90% showed a loss of hock flexion. No cat showed signs of a root signature and only 5 cats (50%) showed changes in sensory. Remember, these cases are MONOparesis or plegia! No paraplegia/paresis would be expected for this disease.
Which nerve was commonly affected?
Tibial nerve: dogs - 16%; cats 20%
Peroneal nerve: dogs - 37%, cats - 60%
Sciatic nerve (common trunk): dogs - 47%, cats - 20%
What are the most common etiology?
The most common cause of sciatic nerve injury in dogs was bite wounds (24%) followed by surgery (TPLO, TPO, DPO, Modified retinacular imbrication, or removal of an intramedullary pin; 18%), and then trauma. I must add here that the bite wounds were caused by wild board. Wild boar! It's Italy, remember? The most common cause of sciatic nerve injury in cats was pelvic trauma (50%), followed in equal amounts by surgery for a femoral fracture (20%), and an IM injection (20%). Only 1 cat sustained a bite, and it was from a dog. Apparently, cat's aren't tasty to wild boar. Or they're faster. (Or not used for hunting wild boar??)
What was the outcome?
A poor prognosis was deemed one that resulted in euthanasia, arthrodesis of the joint or amputation of the limb due to poor function. A good prognosis did not necessarily mean a return to normal, but instead indicated limb function had improved. Animals that were able to flex and extend their tarsus had a significantly better long-term prognosis than those that couldn't. Furthermore, loss of deep pain was NOT a prognostic indicator in this study. This is different than spinal cord studies in which the loss of deep pain is a strong prognostic indicator. Peripheral nerves can regenerate and therefore this loss wasn't useful for predicting recovery. Overall, 9 of 32 dogs (28%) and 1 of 9 cats had a negative outcome. This suggests a favorable long-term outcome for this population of animals.
Thanks for reading! A quick reminder that I am away until Thursday (May 9) so you may experience a delayed response to emails, texts or phone calls. Happy Mother's Day to all who celebrate!