Neurology Case of the Month (March 2013): HL LamenessWritten on March 01, 2013 by Mark. Troxel, DVM, DACVIM (Neurology) Hospital: Massachusetts Veterinary Referral Hospital

Signalment: 4yr FS Rottweiler

History: Patient was referred to the Surgery Department for evaluation of left pelvic limb lameness of 1-month duration. No improvement with Rimadyl and tramadol. Orthopedic examination was within normal limits so a neurology consultation was requested.

Case Video:

 

Questions to ask yourself:

  1. What is your neurolocalization?
  2. What are the top differential diagnoses?
  3. Why are the patellar reflexes exaggerated?

SCROLL DOWN TO SEE NEURO EXAM DETAILS AND ANSWERS

 

 

 

 

 

 

 

 

Neurological exam:

Mental status: BAR
Gait/posture: Ambulatory with a somewhat crouched HL gait, short/choppy hind limb gait at times, and intermittent LHL lameness
Cranial nerves: WNL
Postural reactions:
Absent CP/hop boths HLs
Spinal reflexes: Exaggerated patellar reflexes bilaterally, markedly decreased cranial tibial LHL
Withdrawal: Absent at hocks bilaterally, normal FLs
Spinal pain: LS vs. hip pain
Muscle tone: Normal x 4
Muscle atrophy: None
Pain sensation: Normal x 4
Cutaneous trunci:WNL bilaterally

 

Neurolocalization: L6-S1 spinal cord / Cauda equina

 

 

Differential diagnoses

  • Intervertebral disk herniation/protrusion
  • LS instability
  • Neoplasia
  • Chronic diskspondylitis with secondary nerve/cord impingement from inflammatory/infectious tissue
  • Inflammatory/infectious disease
  • Concurrent orthopedic disease (e.g., hip dysplasia / osteoarthritis)

 

Diagnostics

  • CBC/biochemical profile: NSF
  • Lumbar/pelvic/hip radiographs: Spondylosis deformans at L7-S1, normal coxofemoral joints, no evidence of diskspondylitis
  • MRI: L7-S1 intervertebral disk protrusion/herniation, narrowed L7-S1 disk space, enlarged L7 nerve roots bilaterally that were contrast enhancing, LS spondylosis deformans

 

Preliminary diagnosis
L7-S1 disk protrusion with secondary neuritis vs. lymphoma vs. other neuritis

 

Treatment

  • The patient was treated with an anti-inflammatory dose of prednisone while the owners considered surgery and there was moderate improvement
  • L7-S1 dorsal laminectomy 1 week later: Found moderate amount of extruded disk material and chronic hemorrhage/blood clots. The L7 nerve roots were enlarged, but not as dramatically as expected based on the MRI.

 

Prognosis
The prognosis for LS intervertebral disk protrusion/herniation is generally good to excellent in pet dogs that are treated by dorsal laminectomy.

 

Why were the patellar reflexes exaggerated?
This patient had a lower motor neuron (LMN) lesion affecting the L6-S1 portion of the spinal cord or sciatic nerves. As a result, there was decreased tone in the flexor muscles of the stifle. The flexor muscles normally dampen the patellar reflex to a degree. Without that normal antagonism in this patient, the knee jerk becomes exaggerated.

This is in contrast to the norm in which increased reflexes are usually a sign of upper motor neuron (UMN) disease. Lesions affecting the UMNs lead to decreased inhibitory influence on LMNs. As a result, there is an excessive motor response. An increased patellar reflex usually suggests the lesion is cranial to L3.

So, how do you tell whether the patellar reflex is exaggerated due to an UMN lesion or sciatic dysfunction? Patients with an UMN lesion should have an intact withdrawal reflex, while patients with L6-S1 spinal cord/sciatic nerve dysfunction will have decreased to absent withdrawal in the affected limb(s).

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