Clinical Signs: Is It Degenerative Lumbosacral Stenosis (DLSS)?

Degenerative lumbosacral stenosis (DLSS) is the most common disease affecting the peripheral nervous system to be found in aged medium-sized and large dogs. The intervertebral disc space of L7 and S1, including the associated ligaments, is usually affected. Because the spinal cord segments are shorter than their respective vertebrae, the spinal cord ends at the level of L6 in most of dogs. DLSS occurs due to stenosis of the lumbosacral vertebral canal leading to compression of the blood vessels and nerves which form the cauda equina. As a consequence a lesion localized at L7-S1will induce lower motor neuron signs .

Anatomically following nerves might be affected by the disease:

• The sciatic nerve (L6–L7–S1) provides motor innervation to the semimembranosus, semitendinosus and biceps femoris muscles. More distally, it branches into the tibial nerve (which controls the gastrocnemius, popliteal, and the superficial and deep digital flexor muscles) and the peroneal nerve (which innervates the tibialis cranialis, fibularis longus and the long digital extensor muscles). This nerve complex is also responsible for the sensory innervation of the whole of the hindlimbs distal to the knee with exception of a shallow medial strip innervated by the saphenous branch of the femoral nerve.
• The pudendal nerve (S1–S2–S3) provides motor innervation to the external anal sphincter and the caudal rectus muscle. It provides sensory innervation to the prepuce, peritoneum, vulva and scrotum.
• The pelvic nerve (S1–S2–S3) innervates the smooth muscles of the bladder and rectum.
• The caudal nerves (Cd1–Cd5) are responsible for the motor and sensory innervation of the tail.

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