Lastly, there can be paresis of the tail as demonstrated by an inability to wag the tail or raise the tail during urination
or defecation. Occasionally, affected dogs self-mutilate their tails.2
Neurologic examination findings range from pain as the sole finding to severe motor and sensory deficits. As mentioned previously,
the pelvic limb gait may be shortened and choppy with a plantigrade stance. Often the gait has characteristics similar to
those of lameness from orthopedic disease. Postural reaction deficits can be observed with hopping, hemiwalking, or, in smaller
patients, extensor postural thrust. Proprioceptive positioning (often referred to as conscious proprioception) may be delayed. The withdrawal reflex can be reduced. Likewise, the cranial tibial and gastrocnemius reflexes may be reduced
or absent, though these reflexes are not reliably detected in normal dogs.6 However, the patellar reflex is normal. Occasionally, the patellar reflex may be brisk, which is known as pseudohyperreflexia.
18 The exaggerated reaction is the result of a lack of tone from the caudal thigh muscles rather than a lack of inhibition by
the descending upper motor neurons as seen in spinal cord lesions cranial to the L4 spinal cord segment.
With passive range of motion of the limb, you may note hypotonia, a quality of the flaccid paresis or paralysis seen with
lower motor neuron disease. Similarly, decreased tail tone may be apparent. On palpation, you may detect atrophy of the semimembranosus,
semitendinosus, gastrocnemius, and cranial tibial muscles, which are innervated by the sciatic nerve and its two main branches,
the tibial and peroneal nerves. The perineal reflex may be reduced or absent.
Evaluation of the anus may reveal a dilated anal sphincter. Digital rectal examination may uncover decreased tone of the external
anal sphincter. Simultaneous rectal examination and evaluation of the perineal reflex elicited by palpating the prepuce (innervated
by a branch of the femoral nerve) or penis or vulva (innervated by a branch of the pudendal nerve) may reveal a decrease in
strength of contraction of the external anal sphincter. Additionally, you may elicit a painful response during digital rectal
palpation if you apply pressure to the ventral L7-S1 articulation.
Palpation of the bladder may reveal a large bladder that is easily expressed manually. Alternatively, you may note constant
dribbling of urine. In female dogs, the perineum may also be wet with urine. You may also detect a painful response when applying
pressure over the lumbosacral articulation. When palpating over the lumbosacral joint, take care to differentiate whether
a painful response is related to lumbosacral disease or due to an orthopedic condition. Occasionally, positioning the patient
in lateral recumbency during palpation can help eliminate pressure transmitted across the joints of the pelvic limbs. A test
often used to detect a painful response to manipulation of the lumbosacral joint is extension of the coxofemoral joints. Extending
the coxofemoral joints extends the lumbosacral joint, which may elicit a painful response; however, it is often difficult
to distinguish painful coxofemoral disease from lumbosacral pain.
Disease affecting the lumbosacral articulation rarely results in metabolic derangement. While hematologic and biochemical
tests rarely contribute to the diagnosis, evaluation is warranted because patients occasionally have concurrent illnesses.
Urinalysis may reveal evidence of bacterial cystitis secondary to urethral sphincter incompetence. Perform a bacteriologic
culture in patients with evidence of bacterial cystitis.
Electrophysiologic testing can aid in the diagnosis of lumbosacral disease, but it rarely helps identify a definitive cause.
Instead, it supports clinical suspicion of lumbosacral disease. Additionally, electrophysiologic evaluation of the thoracic
limbs may uncover a more generalized lower motor neuron disease, thereby eliminating lumbosacral disease from further consideration.
Electrophysiologic tests should include electromyography and nerve stimulation testing. Evaluating sensory nerve conduction
and the F wave may provide additional information, but their usefulness needs further investigation. In one report of 13 dogs,
electromyogram abnormalities were identified only in dogs with compression seen at surgery, and no abnormalities were identified
in dogs lacking compression.24 Furthermore, five of six dogs studied had normal motor nerve conduction velocity of the sciatic nerves but reduced amplitude
and polyphasic dispersion of the compound muscle action potential indicative of axonal damage.24
Without a doubt, a diagnosis of degenerative lumbosacral stenosis relies heavily on imaging procedures. The most commonly
used imaging techniques include plain radiography, myelography, epidurography, computed tomography (CT), and magnetic resonance