Surgery STAT: Diagnosing intervertebral disk disease

Intervertebral disk disease (IVDD) is one of the most common conditions affecting chondrodystrophic dogs. Signalment, history and thorough neurologic examination are paramount in diagnosing and determining a treatment plan for animals affected with IVDD.

Photo 1: It is important to support the trunk to rule out primary musculoskeletal weakness as the cause for delays in foot correction.

Chondrodystrophic breeds, such as Dachshunds, older than 2 years of age are predisposed to acute extrusion of the nucleus pulposus (Hansen Type I) because their disks begin to deteriorate shortly after birth. Non-chondrodystrophic breeds, such as German Shepherds, more often have a fibrous degeneration of their disks, resulting in a protrusion of the outer annulus (Hansen Type II).

Photos 2 and 3: Decreased patellar (left), sciatic and hind-limb withdrawal (right) reflexes may indicate a lower motor neuron lesion (between L4 and S1).

Dogs under 2 years of age exhibiting the signs of IVDD should be evaluated for other neurologic conditions, such as meningitis, discospondylitis, vertebral luxation or fracture, toxoplasmosis, neospora and syringomyelia.

While many dogs with spinal pain will vocalize, some may exhibit more subtle signs, such as tremors, difficulty rising or an altered body posture. Dogs with cervical pain often maintain a ventroflexed position of their head and neck. Dogs with thoracolumbar pain may have a hunched posture, while those with lumbosacral pain tend to keep a lower or "tucked" tail position.

Abdominal pain and thoracolumbar spinal pain may cause similar signs; therefore it is important to perform a thorough abdominal palpation during your physical exam. Cranial nerve examination should be performed to help rule out intracranial disease, such as hydrocephalus or brain tumor.

Neurolocalization is accomplished through a series of examinations (Table 1, p. 48). Postural reflexes are tested to assess conscious proprioception. When testing proprioception, it is important to support the trunk to rule out primary musculoskeletal weakness (i.e., bilateral cranial cruciate injury) as the cause for delays in foot correction (Photo 1).

Table 1: Neurolocalization in dogs with advanced IVDD

Decreased patellar (Photo 2), sciatic and hind-limb withdrawal (Photo 3) reflexes may indicate a lower motor neuron lesion (between L4 and S1). Increased patellar reflexes usually indicate an upper motor neuron lesion (lesion cranial to L4); however, the patellar reflex occasionally may be brisk despite the presence of a lower motor neuron lesion as seen with pseudohyperreflexia in some dogs with lumbosacral disease.

Evaluation of withdrawal and perineal reflexes will help clarify the neuro-localization in these cases. Decreased biceps, triceps and withdrawal reflexes in the forelimbs are consistent with a lower motor neuron lesion of the cervical spine (lesion between C4 and T2).

Evaluating dogs for spinal hyperesthesia may be helpful with neuro-localization. External landmarks for anatomic localization include the transverse processes (wings) of C6, the last rib (T13) and the ilial crest of the pelvis (L7-S1).

Digital pressure is applied dorsally to the thoracolumbar epaxial muscles lying adjacent to the dorsal spinal processes. In the cervical region, digital pressure is applied ventrally where there is less musculature. Pressure is applied caudal and lateral to the trachea, directly on the vertebrae. Hyperextension of the head and neck to evaluate for cervical pain should be avoided due to risk of exacerbating spinal-cord compression.

When evaluating the patient for deep pain sensation, it is critical to see a conscious response from the animal after pinching the toe. Simple withdrawal of the foot without a conscious response is a local spinal reflex that does not reflect the presence of deep pain sensation.

Dr. Jeff D. Brourman is an ACVS board-certified surgeon who is with WestVet Animal Emergency and Specialty Center in Garden City, Idaho. His research interests include cardiothorsic surgery and microvascular surgery.