Prognostic Utility of F-Waves in Paraplegic Dogs With Absent Pain Perception Secondary to Intervertebral Disc Extrusion

Abstract

Background: Approximately 50%-60% of paraplegic deep pain negative (DPN) dogs secondary to thoracolumbar intervertebral disc extrusion (TL-IVDE) recover ambulation after surgery. Mean F-wave duration has been associated with injury severity in TL-IVDE in dogs, but the relationship to outcome is unknown.

Objective: Evaluate the prognostic utility of F-waves in DPN dogs secondary to TL-IVDE treated surgically.

Animals: Thirty client-owned, acutely paraplegic DPN dogs secondary to TL-IVDE were managed surgically.

Methods: Multi-center prospective and observational study. F-waves were performed at baseline (within 24 h post-operatively), 2-4 weeks and 3 months post-operatively. Outcome was categorized as successful or unsuccessful, with success defined as independent ambulation at 3 months post-operatively. F-wave variables were compared between dogs with a successful or unsuccessful outcome and over time using generalized estimating equations. Receiver-operating characteristic curves were generated for baseline F-wave variables.

Results: F-waves were well-tolerated in all dogs. Of 30 enrolled dogs, 12 dogs had a successful outcome, 10 dogs were unsuccessful, and 8 dogs were removed from outcome analysis (3 progressive myelomalacia, 1 severe spinal shock, 2 technical error, and 2 unknown outcome). Baseline mean F-wave duration (displayed as median (range)) was longer in unsuccessful dogs (31.7 (11.4-60.8) ms) versus successful dogs (19.6 (10.8-27.3) ms), p = 0.003. Mean F-wave duration > 28.5 ms was 70% sensitive (95% confidence interval (CI): 40%-100%) and 100% specific (95% CI: 100%-100%) in predicting an unsuccessful outcome.

Conclusions and clinical importance: F-waves performed shortly post-operatively could aid in predicting outcomes in DPN dogs secondary to TL-IVDE treated surgically.

Keywords: canine; deep pain negative; electrodiagnostics; intervertebral disc herniation.

FIGURE 1

Example F‐wave recordings from the initial visit (baseline) in a 3‐year‐old spayed female Dachshund with L1–L2 IVDE. The dog had an unsuccessful outcome remaining paraplegic deep pain negative. One trace is isolated at the bottom of the figure to distinguish it from the remaining waveforms and to outline specific variables. The dashed double‐headed arrow indicates the F‐wave duration, the solid double‐headed arrow represents the maximum F‐wave amplitude, and the horizontal bracket highlights the after‐discharge activity.

FIGURE 2

Example F‐wave recordings from the initial visit (baseline) in a 4‐year‐old neutered male Pomeranian who developed progressive myelomalacia secondary to T12–T13 IVDE. At the time of the recording, the patient was paraplegic deep pain negative but had not yet shown clinical signs of progressive myelomalacia. M‐waves are present on the left side of the screen, but there are no visible F‐waves.

FIGURE 3

Example F‐wave recordings from the initial visit (baseline). (A) A 3‐year‐old neutered male Maltese dog with T12–T13 IVDE. The dog had a successful outcome and was deep pain positive. (B) A 4‐year‐old intact male mixed breed dog with T12–T13 IVDE. The dog had a successful outcome but remained deep pain negative (spinal walker). (C) A 3‐year‐old spayed female Dachshund with L1–L2 IVDE. The patient had an unsuccessful outcome remaining paraplegic deep pain negative. In example C compared to A and B, note the longer F‐wave duration, higher F‐wave amplitude, shorter F‐wave latency, and prominent after‐discharge activity.

FIGURE 4

Example F‐wave recordings from the initial visit (baseline) in two dogs with an unsuccessful outcome. (A) A 4‐year‐old female French Bulldog exhibiting severely prolonged (> 100 ms) F‐wave duration that did not return to the baseline during the recording limit of 100 ms. (B) A 5‐year‐old spayed female French Bulldog exhibiting severe after‐discharge activity (score > 2.5/3).