Hansen Type I and Hansen Type II Disc Disease

Hansen Type I and Hansen Type II Disc Disease

Introduction

Intervertebral disc disease (IVDD) is a common and debilitating condition in dogs, affecting the intervertebral discs that serve as cushions between the vertebrae of the spine. IVDD can lead to severe pain, neurological deficits, and even paralysis. The disease is categorized into Hansen Type I and Hansen Type II disc disease, each with distinct pathophysiological mechanisms and clinical presentations. Understanding these differences is crucial for effective diagnosis, treatment, and management.

Etiology

Hansen Type I Disc Disease

Hansen Type I disc disease primarily affects chondrodystrophic breeds such as Dachshunds, Beagles, and Cocker Spaniels. It is characterized by early degeneration and calcification of the nucleus pulposus, leading to disc extrusion. Genetic predisposition plays a significant role in the development of this condition.

Hansen Type II Disc Disease

Hansen Type II disc disease is more commonly seen in non-chondrodystrophic breeds and typically occurs in older dogs. This type involves a gradual degeneration of the annulus fibrosus, leading to disc protrusion rather than extrusion. Breed predisposition is less pronounced, but large breeds like German Shepherds and Labradors are more frequently affected.

Pathophysiology

Hansen Type I Disc Disease

In Hansen Type I, the nucleus pulposus undergoes chondroid degeneration, becoming calcified and less hydrated. Under mechanical stress, the weakened annulus fibrosus ruptures, causing the calcified nucleus pulposus to extrude into the spinal canal. This acute extrusion compresses the spinal cord and nerve roots, leading to severe pain and neurological deficits.

Hansen Type II Disc Disease

Hansen Type II involves fibroid degeneration of the annulus fibrosus, resulting in its weakening and subsequent bulging into the spinal canal. Unlike the acute extrusion seen in Type I, Type II is characterized by a chronic, progressive protrusion. The spinal cord and nerve roots are subjected to prolonged compression, leading to gradual onset of clinical signs.

Clinical Presentation

Hansen Type I Disc Disease

The clinical signs of Hansen Type I disc disease are typically acute and severe. They include:

- Severe pain: Often sudden in onset, localized to the affected spinal region.

- Neurological deficits: Ranging from paresis to paralysis, depending on the degree of spinal cord compression.

- Proprioceptive deficits: Impaired ability to sense limb position.

- Loss of deep pain perception: In severe cases, indicating a poor prognosis.

Hansen Type II Disc Disease

Hansen Type II disc disease presents with more gradual and progressive clinical signs:

- Chronic pain: Less severe than Type I, but persistent and progressive.

- Mild to moderate neurological deficits: Develop slowly over time.

- Weakness and ataxia: Particularly in the hind limbs.

- Gradual loss of proprioception: Often subtle and progressive.

Diagnosis

Clinical Examination

A thorough neurological examination is essential to localize the lesion and assess the severity of the neurological deficits.

Diagnostic Imaging

Radiography

Plain radiographs can show disc space narrowing, calcification of the discs, and other bony changes, but are not definitive for IVDD.

Myelography

Myelography involves injecting a contrast agent into the subarachnoid space to visualize the spinal cord and identify compressive lesions.

Computed Tomography (CT)

CT provides detailed images of the bony structures and is particularly useful for identifying calcified disc material in Hansen Type I disease.

Magnetic Resonance Imaging (MRI)

MRI is the gold standard for diagnosing IVDD as it provides excellent visualization of both the spinal cord and soft tissue structures, including the intervertebral discs.

Treatment

Hansen Type I Disc Disease

Conservative Management

Conservative treatment includes strict cage rest, anti-inflammatory medications, and analgesics. This approach is often effective for mild to moderate cases.

Surgical Management

Surgical intervention is indicated for severe cases or when conservative management fails. Common procedures include:

- Hemilaminectomy: Removal of part of the vertebral lamina to decompress the spinal cord.

- Ventral slot procedure: Decompression of the cervical spine by removing part of the intervertebral disc and adjacent vertebral body.

Hansen Type II Disc Disease

Conservative Management

Similar to Type I, conservative treatment involves rest, anti-inflammatory medications, and physical therapy. It is often the first line of treatment due to the chronic nature of the disease.

Surgical Management

Surgery is considered when conservative management fails or when there is significant neurological compromise. Procedures include:

- Dorsal laminectomy: Removal of the vertebral arch to relieve pressure on the spinal cord.

- Fenestration: Removal of disc material to prevent further protrusion.

Prognosis

Hansen Type I Disc Disease

The prognosis for Hansen Type I depends on the severity and duration of the neurological deficits. Dogs with mild deficits and those treated promptly have a good to excellent prognosis. However, the prognosis is guarded to poor for dogs with severe deficits or loss of deep pain perception.

Hansen Type II Disc Disease

The prognosis for Hansen Type II is generally more variable. Dogs with mild to moderate deficits often respond well to conservative management, while those with significant deficits may require surgical intervention. Chronic cases may have a guarded prognosis due to the prolonged nature of spinal cord compression.

Conclusion

Hansen Type I and Type II disc disease are distinct entities with different etiologies, pathophysiological mechanisms, clinical presentations, and treatment strategies. Understanding these differences is crucial for effective diagnosis and management. Advances in diagnostic imaging and surgical techniques have improved the prognosis for affected dogs, but early recognition and intervention remain key to successful outcomes.

References

1. Brisson, B. A. (2010). Intervertebral disc disease in dogs. Veterinary Clinics of North America: Small Animal Practice, 40(5), 829-858.

2. Chambers, J. N. (2018). Hansen Type I and II intervertebral disc disease. In Veterinary Surgery: Small Animal (pp. 444-454). Elsevier.

3. McKee, W. M., & Downes, C. J. (2018). Diagnosis and management of Hansen type I intervertebral disc disease. Journal of Small Animal Practice, 59(4), 199-208.

4. Olby, N. J. (2010). Advances in the management of acute spinal cord injury in dogs and cats. Journal of Veterinary Internal Medicine, 24(3), 516-531.

5. Levine, J. M., & Hillman, R. B. (2019). Intervertebral disc disease: Diagnosis and treatment. Veterinary Clinics of North America: Small Animal Practice, 49(5), 911-932.