Degenerative lumbosacral stenosis is a complex acquired condition. It corresponds to degenerative changes in the lumbosacral region of the vertebral column over time, leading to the narrowing of the channels containing the cauda equina (sciatic, sacral and coccygeal nerves): the vertebral canal at the level of the sacrum or the L7-S1 foramina. The reasons for the degeneration are not entirely understood (eg past infection, congenital bony abnormalities such as transitional vertebrae, breed predisposition or activities of the dog, among other factors). The anatomical structures involved are the annulus of the L7-S1 intervertebral disc, the inter-arcuate ligament, the synovial joint capsules of the lumbosacral articular facets or the bone such as the sacral lamina.
Clinical signs
One reasonably certain fact is the slowly progressive nature of the problem with peaks of pain and the need to use analgesic techniques on occasion to maintain the dog’s comfort throughout its life
The clinical signs associated with degenerative lumbosacral stenosis are often vague and are largely the expression of pain (eg unilateral or bilateral pelvic limb lameness, back pain) whereas neurological deficits are rarer. Therefore, the condition may be either over- or under-diagnosed, and in any case is difficult to diagnose. Consequently, the ideal treatment path has remained elusive. Jeffery et al. (2014) provide an interesting take on the challenges associated with the diagnosis and treatment of degenerative lumbosacral stenosis and the paper is ideal for further reading. One reasonably certain fact is the slowly progressive nature of the problem with peaks of pain and the need to use analgesic techniques on occasion to maintain the dog’s comfort throughout its life.
Management of lumbosacral stenosis
The epidural injection of the corticosteroid methylprednisolone acetate (Figure 1) is a therapeutic option to treat episodes of pain. The goal is to deliver this long-acting corticosteroid into the epidural compartment, ie around the roots of the sciatic and sacral nerves. Further detail on the technique is described by Garcia-Pereira (2018). The epidural space communicates with the paravertebral space through the intervertebral foramina from which the roots of the sciatic nerves emerge at the L7-S1 foramina. Thus the epidural injection, typically performed between the L7 and S1 vertebrae, should allow the methylprednisolone acetate to diffuse around the nerves of the cauda equina and their roots, while also reaching the ligamentous structures, the joint capsules of the L7-S1 intervertebral facets and the L7-S1 disc.
Janssens et al. (2009) proposed a protocol consisting of an initial methylprednisolone acetate epidural injection, followed by a second injection approximately 15 days later and finally a third injection six weeks later. After the third injection, the decision and timing of administration was driven by the owner’s request and dogs with recurrence within three months did not receive subsequent injections. In the study, 30 of 38 dogs improved (79 percent) and 20 dogs (53 percent) were considered by their owners to be pain-free over a median follow-up of 46 months (with follow-up ranging from 5 to 66 months). A more detailed follow-up is presented in Figure 2.
Thirty of 38 dogs improved (79 percent) and 20 dogs (53 percent) were considered by their owners to be pain-free over a median follow-up of 46 months
In this study by Janssens et al., it is important to note that cases with the most severe syndromes (eg presence of neurological signs, presence of lumbosacral transitional vertebrae, concurrent orthopaedic conditions) were excluded, and assessment was based on an owner’s questionnaire, which constitutes bias. It is also interesting to comment that in this study the dogs were allowed normal exercise after the epidural injection.
In our experience, a single injection of methylprednisolone acetate to assess the analgesic effect obtained before repeating the procedure may be a useful approach. Gomes et al. (2020) tested this idea in a prospective study where 27 dogs out of 32 (84.4 percent) improved following a single injection. These dogs were then followed up without a repeat injection and received surgery in case of relapse. The complete follow-up is summarised in Figure 3. This shows that a subset of dogs (5 of 32 dogs) may have long-lasting benefits from one injection. The timing for the second injection, or even subsequent injections, remains currently uncertain in the absence of more data.
In our experience, a single injection of methylprednisolone acetate to assess the analgesic effect obtained before repeating the procedure may be a useful approach
Interestingly, a permanent epidural catheter and subcutaneous access port system has just been reported in 11 dogs and appears to be safe over a two-year follow-up period (Bussières et al., 2024). This may constitute an attractive way of managing pain with reduced invasiveness and reduced need for regular anaesthetic in dogs with degenerative lumbosacral stenosis.
It should be noted that the injection can cause mild to moderate pain within 24 to 48 hours after its administration (resulting in lameness or difficulty in getting up, for example). This is normal and the owner should be informed to avoid premature disappointment. The prescription of paracetamol (10mg/kg orally every 8h) is recommended in parallel (note: we are referring only to dogs for this procedure and in this article). It remains a very safe procedure according to Janssens et al. (2009) and Gomes et al. (2020) where no major complication is of note.
Conclusion
In conclusion, epidural injection of methylprednisolone acetate for treatment of degenerative lumbosacral stenosis in dogs is an attractive and relatively non-invasive tool. It is possible that a subset of dogs only requires one injection, while others, as expected from the pathophysiology of the disease, may need repeated injections or surgery.
