Limping - Orthopedic or Neurologic?

Limping is often orthopedic in origin however in some situations limping can be of neurologic origin. Nerve root signature (NRS) sign is observed clinically as a non-weightbearing flexion of one limb, during standing, which may also appear like limping when gaiting. The suspected causes for NRS include vascular compression, inflammation or compression of a nerve root. This is most commonly noted in the thoracic limbs but has been reported in the pelvic limbs also.
In a recent study, a group from NCSU evaluated dogs with cervical disc herniations to see what criteria were present when they had signs of a NRS. This study included 47 dogs. Not surprisingly, all 47 had signs of cervical hyperesthesia with signs like ataxia (n=14), intermittent lameness (n=7), tetraparesis (n=2) and tetraplegia (n=1) being observed less frequently. I personally am not sure how you can identify a dog with a root signature sign if they’re plegic…but apparently, they did! Interestingly (to me) the site of disc herniation was C2-C5 in 20 dogs (43%) and C5-T1 in the other 27 dogs (57%). The nerve roots are supposed to arise from the C6-T2 region which is why it would make the most sense that a NRS sign should involve those nerve roots. Why did the C2-C5 region have NRS signs? Perhaps there was tethering of the nerve roots from "tugging" secondary to a cranially located disc. Perhaps anatomically they had a neve root arise more cranial than typical.
Spinal cord compression was mild in the majority of cases but remember it takes a TON of disc material in the cervical spinal cord to result in compression. Mild spinal cord compression is often surgical because the canal is much more voluminous around the smaller spinal cord (which is different from the thoracolumbar spine). Therefore the canal can contain loads of disc material yet the spinal cord has room to scootch over away from the disc, thus resulting in mild compression. Disc material was almost 3x more likely to be located laterally, within the spinal canal, than medially. Additionally, dogs were 2x more likely to have disc material compressing a nerve root compared to dogs without NRS. The last interesting finding is that 75% of the dogs in this study were over 7 years old. Typical chondrodystrophic disc degeneration with resulting herniation occurs in ages 3-7 year old. Is there a relationship between age, site of disc herniation and NRS or was this coincidental? I’m not sure but felt it was worth of comment.
 
Take away message:
Thoracic limb limping is often orthopedic in origin, however NRS should be considered for cases in which orthopedic disease is not identified. Nerve root signature sign secondary to a cervical disc herniation is more likely to be lateralized and therefore referral for surgical correction is strongly recommended to alleviate the compression to the nerve root.
 
Thanks for reading! Are we through deep winter? I’m not sure but I sure hope you’re staying warm! Please reach out with any questions about root signature sign or other neurologic cases. Have a great week!

Canine Distemper Causing Lameness?

An interesting case report came across my desk awhile ago so I thought I might share some key points with you this week. (Green L, Cook L, et al. Distemper encephalomyelitis Presenting with Lower Motor Neuron Signs in a Young Dog. JAAH 2020)

Signalment: 4 month old spayed female dog

History: The puppy was presented to the neurology service with a several day history of right thoracic limb monoparesis. Key findings in the neurologic examination included axial pain on palpation, thoracic limb lameness, weak withdrawal of the affected limb and a paw replacement deficit in that limb. Absent cutaneous trunci reflex was also noted on the right side. Other than the neurologic findings, the only other interesting finding on physical examination was a mildly febrile state of 102.7F) and crusting of the foot pads.

She was initially managed conservatively however signs progressed to inappropriate mentation which was suspected to be due to the fentanyl patch. This was removed and signs improved however the clients elected to proceed with additional testing at that time.

Neuroanatomic lesion localization? You tell me!! (see below when ready)

Differential diagnoses listed at this time included non-infectious inflammatory conditions (MUE), infectious meningomyelitis, and hemorrhage or trauma.

Diagnostic testing

• Spinal MRI: Abnormalities in the central spinal cord

• Brain MRI: Unremarkable

• CSF: Mild pleocytosis cell count 10/ul: reference < 5/ul) with normal protein and RBC.

• Infectious disease testing: Neospora IFA was negative however the Toxoplasma IgG was markedly elevated with a borderline IgM. Parvovirus testing and cryptococcus antigen testing was negative. PCR on CSF for distemper (CDV) was positive. A whole lot of other infectious diseases were tested for, and negative.
  

Treatment with clindamycin, sucralfate, gabapentin, tramadol, famotidine, metronidazole and a single dose of dexamethasone was started.

Progression: She was discharged 4 days later, but returned due to progressive mentation changes and worsening ambulation. During evaluation she had a focal seizure. (Now we have multifocal neuroanatomic lesion localization!). She was humanely euthanized and submitted for necropsy.

Necropsy: Findings consistent with CDV were found and in addition, immunohistochemistry of the C5 and lumbar spinal cord and strong nuclear and cytoplasmic brown staining for CDV and no staining for Toxoplasma.

What is so noteworthy about this case?

• She was partially vaccinated. Did you know that 40% of dogs with confirmed distemper infection, in one study, were vaccinated? (Tipold A: 1995).

• She had hyperesthesia associated with her neurologic signs. Pain is a very unusual finding for a distemper case and the authors suggest this is the first case report of confirmed CDV in a dog with limb pain.

• The progression from limb to brain is unusual but not unreported.

Take Home Message
A young dog, with multifocal neurologic findings, or findings of spinal pain in conjunction with neurologic findings, may have CDV. I suggest adding this disease to your ever-growing-list of infectious diseases that can cause spinal pain in dogs.

Neuroanatomic lesion localization answer: C6-T2 radiculopathy or neuropathy. There is no evidence of spinal cord involvement initially so a myelopathy is less likely.

As always, thanks for reading! I hope you have a NON-PAINFUL week, that isn't LAME! (Sorry...I just couldn't help myself.)

Root Signature Sign: Neurologic Lameness

It's Wednesday morning and your first consult is a limping dog. You nod...you've got this. Upon examination you cannot find any evidence of joint pain, muscle or bone pain. Not deterred, you radiograph shoulder to foot. Nothing of interest is visible.

What if the lameness is neurologic in origin, you ask yourself?

The most common causes of neurologic lameness in dogs are cervical disc herniation and nerve sheath tumors. Most dogs have neurologic deficits along with their lameness so it is worth a close look at the neurologic examination. Deficits could include reflex deficits, postural reaction deficits and/or pain.
Side note: Did you know that lameness from a neurologic cause is called a root signature sign?

Cervical Disc Herniation
Cervical disc herniation with resulting nerve root impingement occurs from type I or type II disc herniation. Many dogs have cervical pain along with the root signature sign, but not all. Cervical radiographs are non-diagnostic for cervical disc herniations and therefore not often recommended. MRI or CT/myelogram are the diagnostic tests of choice with MRI providing greater detail. Treatment may be medical or surgical. My recommendations for medical management vary by pet, but typically include a NSAID, gabapentin and a muscle relaxant. Additional management with opioids can also be included. Best rest is often recommended for the first 3 weeks. Surgical management is recommended for medically resistant dogs, or if the MRI or clinical signs are severe.

Nerve Sheath Tumor
Nerve sheath tumors are typically slow growing, locally invasive (eventually into the spinal canal) tumors. These are best diagnosed with MRI. Definitive treatment is surgical removal. If surgical removal is not pursued, supportive care with pain management (NSAID or prednisone +/- opioid), muscle relaxant and gabapentin are recommended. Acupuncture may provide additional pain relief. The slow growing nature of nerve sheath tumors means that clinical signs may be present for months before the pain or debilitation becomes life limiting.

Not sure if the patient you are seeing has neurologic disease? This is one of the main functions of a traveling neurologist (me!). Sorting between orthopedic and neurologic causes of lameness can be challenging, especially if you're not comfortable doing the neurologic examination. Please reach out, you're not alone! You can find me on email, or schedule directly online using my website.

Okay, now that we got that out of the way, enjoy that Wednesday morning lameness evaluation!

Happy St. Patty's Day everyone. I have two kids that do Irish dancing so we're really missing the festivities this year, but we look forward to celebrating next year.

Stay safe, stay kind, and I look forward to working with you soon!