Degenerative myelopathy: does laser therapy offer new hope?

Degenerative myelopathy (DM) is a canine genetic disease that occurs later in life and causes relentlessly progressive degeneration of the spinal cord, with no definitive treatment in sight. Of all the treatments and supplements anecdotally promoted for use, to date only physical therapy and rehabilitation have been shown scientifically to slow disease progression and maintain quality of life for longer than untreated dogs. Even so, the condition continues to progress over six to 12 months, despite rehabilitation therapy.

In a new study out of New England,¹ outcomes of DM patients treated with one of two photobiomodulation therapy (PBMT; previously called low-level laser therapy) protocols were compared.

Study design

This nonblinded, retrospective study described clinical outcomes of dogs referred to a specialty physical rehabilitation facility between 2003 and 2012 for treatment of DM. Definitive or presumptive diagnosis was made using one or more of the following tests: DNA testing for the SOD1 mutation, magnetic resonance imaging of the thoracolumbar spine or postmortem histopathologic evaluation.

Twenty dogs met the inclusion criteria and were sorted into two groups based on the PBMT protocol used in their treatment:

• Protocol A (n = 6) was 904 nm wavelength, 0.5 W, 0.5 w/cm², 8 J/cm², covering a treatment area of 650 to 1,000 cm² in a point-to-point grid pattern consisting of 20 points. Treatment for protocol A lasted 5 minutes 20 seconds.
• Protocol B (n = 14) was 980 nm wavelength, 6 to 12 W, 1.2 to 2.4 w/cm², 14 to 21 J/cm², covering the same treatment area (650-1,000 cm²) in a continuously moving grid pattern covering the entire area at a rate of one to three inches per second. Treatment for Protocol B lasted 25 minutes to 26 minutes 15 seconds.

In addition, all dogs also had twice weekly in-clinic rehabilitation therapy, including range of motion, stretching, standing/proprioceptive exercises, stabilization and core exercises, walking obstacles and underwater treadmill walking. Home exercise protocols were also prescribed for all dogs.

Results and discussion

Survival time from the start of treatment to the time of euthanasia was significantly longer for dogs in protocol B than in protocol A (27.05 and 6.83 months, respectively). Given the variability in owner decisions regarding euthanasia, the time to non-ambulatory paraparesis may be a more reliable indicator of treatment outcome. The mean time from the start of treatment to the time of non-ambulatory paraparesis was also significantly longer for dogs receiving protocol B compared with protocol A (20.61 and 4.26 months, respectively).

There are several considerations when interpreting these results. Median survival and median time to non-ambulatory status were not reported by the authors, but may be a more reliable outcome measure, as the median values are less influenced by outliers than are mean values; however, the outcomes using PBMT in protocol B nevertheless remain promising. The outcomes from protocol A were similar to those of prior studies^2,3; however, outcomes reported with protocol B surpassed those reported in a prior study evaluating intensive physical rehabilitation in dogs with DM, in which mean survival was 8.5 months in the intensive rehabilitation group, 4.3 months in the moderate rehabilitation group, and 1.8 months in the untreated control group.²

Further studies are needed to confirm these results, particularly where eventual histopathologic evaluation can provide a definitive diagnosis for all enrolled cases. Given the presumptive nature of antemortem diagnosis, despite positive DNA test results, the findings in this study should be interpreted cautiously. This is particularly true as protocol B patients had a mean duration of clinical signs of 11.15 months prior to enrollment. This surpasses the typical outcome of untreated patients and could indicate that a subset of patients in that group did not actually have DM. Additionally, two authors on this paper are employed by the company that manufactures the PBMT device, and participated in data collection and analysis.

Clinical impact

This study reports promising results as to the potential benefit of PBMT in slowing the progression of canine DM. Independent, third-party studies evaluating patients in which definitive diagnosis is eventually acquired are needed to confirm these outcomes.

References

1. Miller LA, Torraca DG, De Taboada L. Retrospective observational study and analysis of two different photobiomodulation therapy protocols combined with rehabilitation therapy as therapeutic interventions for canine degenerative myelopathy. Photobiomodul Photomed Laser Surg 2020;38(4):195-205.

2. Kathmann I, Cizinauskas S, Doherr MG, et al. Daily controlled physiotherapy increases survival time in dogs with suspected degenerative myelopathy. J Vet Intern Med 2006;20:927-932.

3. Coates JR, March PA, Oglesbee M, et al. Clinical characterization of a familial degenerative myelopathy in Pembroke Welsh Corgi dogs. J Vet Intern Med 2007;21:1323-1331.