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Review Article: Lumbosacral Disease – Diagnosis and Treatment

Lumbosacral disease (a.k.a. lumbosacral syndrome; degenerative lumbosacral stenosis) is a relatively common condition, usually seen in active medium to large breed dogs: From a caseload of 75 MRI-confirmed dogs seen here between 2004-2010, well-muscled terriers, retrievers, spaniels, German shepherd dogs, rottweilers and boxers are over-presented. 

fig.1 - parasagittal T1W slice of lumbosacral spine showing an incidental finding of an extradural cyst immediately cranial to the lumbosacral disc. Note: the L7-S1 disc is degenerate and S1 appears transitional.

Age of onset is usually middle-age, but juveniles and geriatrics are occasionally affected.  There appears to be no sex predilection.

Signs are often insidious in onset, initially presenting as a reluctance to jump or with progressive exercise intolerance.  Owners may describe nerve-root signs such as intermittent, poorly localisable lameness or licking and chewing of the pelvic region or the distal limb.  Signs are usually exacerbated by vigorous exercise.  The vast majority of cases presenting here have bilateral pelvic limb involvement which can sometimes make gait abnormalities harder to detect.  Advanced cases may develop a combination of the following; atrophy of the hamstring muscle group, mono- or para-paresis, loss of voluntary movement of the tail and urinary/ faecal incontinence.

Diagnosis

fig.2 - transverse T2W slice at level of a normal lumbosacral disc for comparison. Note the presence of fat signal throughout both intervertebral foramen.

It is important that patients undergo a full clinical (including rectal), orthopaedic and neurological examination to determine their health status and rule out other differentials such as prostatic, urethral or anal sac disease.  CSF analysis may also be used to eliminate primary inflammatory CNS disease. 

Mildly affected cases may not display overt lameness, but will sometimes adopt a characteristic ‘tucked-up’ posture at rest.

Palpation of the hamstring muscle groups may reveal a degree of atrophy .  Hypersensitivity of the sciatic nerve may also be demonstrable on deep palpation of the nerve through the biceps femoris muscle.

The most reliable clinical finding is discomfort on palpation or manipulation of the lumbosacral joint.  Stoic or mildly affected cases may not respond initially, but repeat examinations will usually identify the locus of pain accurately.  A useful manipulation is to place the examiner’s chin over the L7-S1 joint so as to free up both hands to clasp the proximal pelvic limbs; by exerting a proximal force vector along the axis of the limbs the lumbosacral joint is extended without extension of the hips; occult hip pain might ……………………………….otherwise confuse localisation of the problem.

fig.3 - sagittal T2W slice showing dorsoventral stenosis of the neural canal.

Neurological testing is often unremarkable in the early stages of the disease.  Advanced cases may develop pelvic limb proprioceptive deficits, poor hock flexion on withdrawal and pseudohyperreflexia of the patella reflex due to loss of hamstring muscle tone.

Imaging

fig.4 - transverse T2W slice at level of the L6-7 disc - there is left lateral deformation to compress the L6 outflow tract.

fig.5 transverse T2W slice at level of lumbosacral disc - there is bilateral deformation to compress both L7 outflow tracts.

Survey radiology of the lumbosacral joint may reveal degenerative changes, including disc space narrowing, spondylosis across the disc space or around the facet joints, as well as end-plate sclerosis.  Transitional vertebrae may also be encountered, which often prove significant in this region of the spine.  Bone loss at the end-plates may be seen in advanced cases of discospondylitis.  However, many cases affected by lumbosacral disease will show minimal radiographic changes.  Conversely, the presence of marked radiographic changes is not a reliable marker of clinical disease.  Stressed, flexed and extended lateral views of the caudal lumbar spine may be useful to demonstrate ………………………………………………………………..instability or subluxation of the joint.

Myelography and ‘discography’ are not helpful (even where the dural sac extends caudal to the L7-S1 disc) as more often than not, compression of neural structures occurs within the exit (abaxial)-zone of the intervertebral foramen; such lesions would be missed with these imaging techniques – leading to a high incidence of false negatives.

fig.6 - parasagittal 3D T1W slice showing loss of fat signal around the L7 nerve root due to impingement - compare to L5 & 6 foramen.

CT may be used to outline changes to the L7-S1 intervertebral disc and identify narrowing of the neural canal and/ or the intervertebral foramen, but this imaging modality will not give sufficient information regarding subtle changes to the soft tissues to provide a complete assessment of the condition. 

It is well established that the gold standard for the definitive diagnosis of lumbosacral disease is MRI.  This modality has inherent advantages in eliminating other differentials, characterised by soft-tissue pathological processes such as tumours and extradural cysts which can mimic lumbosacral disease but are difficult to rule out by other means (see fig.1).

Several MRI sequences are routinely acquired when assessing patients for this condition:

  • Standard T1 & T2W sagittal and transverse slices will allow accurate assessment of degenerative changes to the intervertebral discs, facet joints and will localise sites of compression along the nerve root outflow tracts so as to characterise the condition as central, uni– or bi-lateral (figs. 2-5). 
  • 3D (thin) parasagittal slices are also helpful to further characterise foraminal entrapment, impingement or claudication of the nerve roots (fig. 6).
  • Dorsal STIR slices are also used to identify pre-stenotic hyperplasia of affected nerve roots.  This is a reliable marker for clinical disease (fig. 7).

Management

fig.7 dorsal STIR slice showing enlarged, right L7 nerve root pre-stenosis. Left nerve root also appears enlarged as compared to L6 nerve roots.

With few exceptions, lumbosacral disease is a progressive condition.  Owners who elect for conservative therapy (modification of exercise regime, including targeted physiotherapy and analgesia) should be advised that long-term compression of neural structures eventually results in irreversible malacia; those animals presenting with end-stage disease (severe paraparesis and/ or incontinence) may not benefit significantly from surgery.  However, the majority of cases would be expected to show a significant clinical improvement in the short-to-medium term with non-surgical treatment.  Combinations of gabapentin, tramadol and anti-inflammatory doses of steroid may be used to reduce pain associated with acute flare-ups.  However, owners should be further advised that cases will often relapse once exercise levels are increased.

Given that many patients present relatively late in the course of the disease – once they can no longer cope with their previously active life-style – recommendations involving indefinite restriction of their pet’s exercise are understandably unpopular with owners; a discussion of the benefits of surgical therapy may therefore be appropriate as soon as the diagnosis has been confirmed. 

Surgery should also be considered where response to conservative management has been poor.

Surgical management of lumbosacral disease is controversial.  Reported procedures advocate removal of the dorsal annulus of the L7-S1 disc (possibly combined with fenestration of the nucleus pulposus, and debridement of the soft tissues around the facet joints) prior to stabilisation of the joint(s) with implants.  However, it is our experience that patients can expect to achieve a sustained clinical improvement without the need to stabilise the joint, provided sufficient decompression has been achieved; we routinely perform dorsal laminectomy of the L7-S1 joint, extended bilaterally to remove the caudal articular processes of L7 so as to ‘de-roof’ the foramen and permanently relieve the pressure along the nerve-root outflow tracts.  Long-term follow-up of such cases suggests the majority of patients can resume their active life-styles with minimal signs of recurrence. 

Of further note is the continued evolution of foraminal surgery due to on-going concerns regarding chronic instability of the L7-S1 joint.  A dorsolateral foraminotomy technique has been proposed in an attempt to address these concerns1.

References/ Further Reading:

1.  Goedde T., Steffen F. (2007) Surgical Treatment of Lumbosacral Foranimal Stenosis Using a Lateral Approach in Twenty Dogs with Degenerative Lumbosacral Stenosis. Vet Surg 36(7) 705-13.

2. Sharp NJ & Wheeler SJ (2005) Lumbosacral Disease in Small Animal Spinal Disorders.  Diagnosis and Surgery p.181-209 Elsevier Mosby, London.