Clinical Exposures: Intervertebral disk disease: An unusual cause of a cat's lameness and tail weakness

Clinical Exposures: Intervertebral disk disease: An unusual cause of a cat's lameness and tail weakness

Mar 01, 2006

A 10-year-old 8.6-lb (3.9-kg) spayed female domestic medium-haired cat had been evaluated by the referring veterinarian because of lethargy, right pelvic limb lameness, lumbar discomfort, reluctance to jump, and tail weakness. The owner had reported that the signs had appeared acutely and had progressively worsened over two weeks.

The cat had been adopted as a stray about five years earlier and was currently allowed indoors and outdoors. The results of a feline leukemia virus (FeLV) antigen test performed eight months earlier had been negative, and routine vaccinations, including FeLV, were current.

A radiographic examination of the pelvis, stifles, and lumbosacral spine performed by the referring veterinarian had revealed a narrowed L6-L7 intervertebral disk space. A compressive myelopathy had been suspected, and the cat had been hospitalized and treated empirically with dexamethasone (1.29 mg/kg orally once daily for five days) and butorphanol tartrate (0.4 mg/kg subcutaneously as needed). The cat had been referred to the Veterinary Neurological Center in Las Vegas for further evaluation and diagnostic testing after it had shown no improvement.

Physical and neurologic examinations

On presentation at the Veterinary Neurological Center, a physical examination revealed a bright, alert animal with a temperature of 102 F (38.9 C), heart rate of 210 beats/min, and respiratory rate of 50 breaths/min. The oral mucous membranes were pink and moist, and the capillary refill time was 1 second. Other than mild gingivitis, a flaccid tail, and perianal soiling with urine and feces, the cat appeared to be in good physical condition.

Figure 1A. A lateral radiograph showing a large mineralized opacity between L6 and L7.
A neurologic examination revealed delayed hopping in the right pelvic limb, reduced hock flexion bilaterally, an absent cutaneous trunci reflex at all levels, hyperesthesia on palpation over the lumbosacral spine and tailhead, and an absence of voluntary tail movement. The cat's tail was flaccid, but its gait appeared normal. Anal tone was present, and the bladder was small on palpation. The remainder of the physical and neurologic examinations was unremarkable. The absence of the cutaneous trunci reflex was not necessarily clinically relevant because it can be absent in normal cats. These findings localized the lesion to the caudal lumbar intumescence (L6-S1), or cauda equina.

Differential diagnoses and diagnostic testing

Our differential diagnoses for this cat's progressive myelopathy included neoplasia (primary or metastatic), infectious or inflammatory spinal cord disease (toxoplasmosis, feline infectious peritonitis [FIP], coccidioidomycosis, discospondylitis), or intervertebral disk protrusion or herniation.

The complete blood count results were normal. The serum chemistry profile revealed elevated albumin (4.2 g/dl, normal = 2.5 to 3.9 g/dl) and triglyceride (216 mg/dl, normal = 25 to 160 mg/dl) concentrations. The serum thyroxine concentration was normal (1.1 µg/dl, normal = 0.8 to 4 µg/dl). A urinalysis revealed alkalinuria (pH 7.5, normal = 5.5 to 7), proteinuria (+2, normal = negative), and struvite crystalluria (+4, normal = negative). The results of FeLV antigen and feline immunodeficiency virus (FIV) antibody tests, feline toxoplasmosis serologic tests (i.e. IgG, IgM), and a feline coronavirus immunofluorescent antibody test were negative.

Figure 1B
A ventrodorsal radiograph of the cat's spine showing a large mineralized opacity between L6 and L7.

For the spinal diagnostic procedures, anesthesia was induced with thiopental and maintained with isoflurane, and the cat received mechanical ventilation. Survey radiography of the thoracolumbar spine revealed narrowing of the L6-L7 intervertebral disk space and foramen. A large (5 mm diameter), spherical mineralized opacity was identified within the vertebral canal at the level of and just caudal to the L6-L7 intervertebral disk space (Figures 1A & 1B).