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Disorders of the Spinal Column and Cord in Dogs

By William B. Thomas, DVM, MS, DACVIM (Neurology), Professor, Neurology and Neurosurgery, Department of Small Animal Clinical Sciences, University of Tennessee ; Cheryl L. Chrisman, DVM, MS, EDS, DACVIM (Neurology), Professor of Veterinary Neurology, College of Veterinary Medicine, University of Florida ; Charles E. Rupprecht, VMD, MS, PhD, Director, LYSSA LLC ; Kyle G. Braund, BVSc, MVSc, PhD, FRCVS, DACVIM (Neurology), Director, Veterinary Neurological Consulting Services ; Caroline N. Hahn, DVM, MSc, PhD, DECEIM, DECVN, MRCVS, Senior Lecturer in Veterinary Clinical Neuroscience, Royal (Dick) School of Veterinary Studies, University of Edinburgh ; Charles M. Hendrix, DVM, PhD, Professor, Department of Pathobiology, College of Veterinary Medicine, Auburn University ; Karen R. Munana, DVM, MS, DACVIM (Neurology), Associate Professor, Department of Clinical Sciences, College of Veterinary Medicine,North Carolina State University ; T. Mark Neer, DVM, DACVIM, Professor and Hospital Director, Center for Veterinary Health Sciences, Oklahoma State University ; Robert Wylie, BVSc, QDA

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Disorders of the spinal column and cord include congenital defects (discussed above), degenerative diseases, inflammatory and infectious diseases, tumors, nutritional diseases, injury and trauma, toxic disorders, and vascular diseases.

Degenerative Diseases

Degenerative lumbosacral stenosis is a disorder of the vertebrae in the lower back that causes compression of the nerve roots. It is most common in large breeds of dogs, especially German Shepherds. The cause is unknown. Signs typically begin at 3 to 7 years of age and may include difficulty using the hind legs, tail weakness, and incontinence. Dogs often experience pain when the lower back is touched or moved. Other signs include a loss of paw position sense, muscle wasting, or weakened reflexes in the hind legs. X-rays may show signs of degeneration, but diagnosis requires magnetic resonance imaging (MRI) or computed tomography (CT). Dogs in which mild pain is the only sign may improve with 4 to 6 weeks of rest. Specific treatment requires surgery. The outlook for recovery after surgery is good, although urinary incontinence may continue.

Intervertebral disk disease is a degenerative disease of the spinal column that results in compression of the spinal cord and spinal nerves. It is a common cause of spinal cord disorders in dogs, especially of small breeds, particularly the Dachshund, Beagle, Shih Tzu, Lhasa Apso, and Pekingese. In these breeds, spinal disks can begin degenerating in the first few months of life. A herniated or “slipped” disk causing severe signs can occur suddenly, as early as 1 to 2 years of age. In contrast, disk degeneration in large breeds of dogs typically occurs after the age of 5 years, and signs continue to worsen. Herniated disks are most common in the neck and the middle of the back. A herniated disk in the neck leads to neck pain, stiffness, and muscle spasms. There may be muscle weakness or other signs, ranging from mild partial paralysis in the legs to total paralysis of all legs. A herniated disk in the middle of the back leads to back pain, and possibly curvature in the spine and a reluctance to move. Neurologic signs range from a loss of motor control in the hind legs to paralysis and incontinence. In paralyzed animals, it is important to determine whether pain sensation is present by pinching the toe or tail and watching whether the dog makes a behavioral response, such as a bark or turn of the head.

Diagnosis of herniated disks requires x‑rays, myelography, computed tomography (CT), or magnetic resonance imaging (MRI). Dogs with minimal to moderate signs that can still feel pain often recover with a few weeks of rest. Anti-inflammatory or pain medication can be used, but generally only if the dog can be cage-rested. If the dog increases its activity, the disk(s) may extrude further and worsen the spinal cord compression. Unfortunately, signs recur in 30 to 40% of cases. In dogs with severe neurologic signs, surgery must be performed promptly to relieve the pressure on the spinal cord. Surgery is also needed if drug therapy is unsuccessful and signs return. The outlook for recovery after surgery is good if the dog can still feel pain. If surgery is delayed for more than 48 hours after pain perception is lost, the chances of recovery decrease.

Inflammatory and Infectious Diseases

Infectious and inflammatory diseases of the spinal column and spinal cord include bacterial, rickettsial, viral, fungal, protozoal, and parasitic infections. Many of these diseases, such as meningitis and encephalitis, can also affect the brain. Some of the more common infectious and inflammatory diseases that affect the spinal column or cord are discussed below.

Bacterial Diseases

Diskospondylitis is inflammation of the disk between 2 vertebrae (bones in the spinal column). The vertebrae can also be inflamed without infection of the disk. Causes include a bacterial or fungal infection in the bloodstream or a weakened immune system that allows infections to develop. Diskospondylitis occurs more often in larger breeds. The most common sign is spinal pain, with some dogs also having fever, depression, and weight loss. Neurologic signs can develop due to pressure on the spinal cord or, rarely, spread of infection to the spinal cord. Blood and urine samples can identify the underlying infection. Signs usually disappear within 5 days of treatment with an appropriate antibiotic, but treatment should be continued for at least 8 weeks.

Rickettsial Diseases

Dogs that develop an infection of rickettsia or related bacteria sometimes show signs of spinal cord dysfunction. These bacteria cause disorders such as Rocky Mountain spotted fever and ehrlichiosis, which can lead to swelling in the spinal cord. Blood and cerebrospinal fluid samples can help identify the infection. Antibiotic treatment is given for 2 to 3 weeks. The outlook for a full recovery is good with early treatment, although the neurologic signs occasionally worsen despite treatment.

Viral Diseases

Canine distemper encephalomyelitis, a viral infection that causes swelling of the brain and spinal cord, remains one of the most common central nervous system disorders in dogs worldwide. Neurologic signs may appear suddenly or may worsen slowly and progressively, depending on the location of the swelling. Adult dogs can have fever and pain, and animals sometimes lose motor control or develop paralysis. Definitive diagnosis is difficult without a necropsy. There is no specific treatment, and the outlook for recovery is poor for dogs with severe signs. Vaccination is usually successful in preventing distemper.

Rabies ( Rabies in Dogs) is caused by a viral infection that spreads to the central nervous system from the peripheral nerves. Rabies is common throughout the world except in Japan and some other islands, including New Zealand, Iceland, and Hawaii. Initial signs are extremely variable, and rabies should be considered a possibility in any unvaccinated animal with severe neurologic dysfunction. Signs that the infection has reached the spinal cord include a loss of motor control and progressive paralysis, usually with a loss of reflexes. Affected animals typically, but not invariably, die within 2 to 7 days of when signs begin. There is no treatment. Vaccination is essential for prevention.

Fungal Diseases

Cryptococcus neoformans is the most common fungus to cause a central nervous system infection in dogs. Other fungal organisms may also invade the central nervous system. Infections often affect other organs, such as the lungs, eyes, skin, or bones. Signs of spinal cord infection include partial or total paralysis and spinal pain. Blood or cerebrospinal fluid tests are necessary to diagnose an infection and identify the organism.

Treatment and the outlook for recovery depend on the specific fungus involved. The drug fluconazole is often effective for Cryptococcus infections. Infections with Blastomyces or Histoplasma fungi are difficult to treat, and the outlook for recovery in dogs infected with these fungi is uncertain.

Protozoal Diseases

Neosporosis is caused by Neospora caninum, a microorganism that can cause inflammation of the brain and spinal cord. Infection in young puppies typically causes paralysis with muscle rigidity in one or both hind legs. Other organs, including muscle, liver, and lungs, can also be affected. A blood test or tissue sample can be used to diagnose the infection. Early drug treatment may be effective, but the chances of recovery are poor.

Toxoplasmosis is caused by a protozoan called Toxoplasma gondii, which can occasionally cause inflammation of the brain and spinal cord. Dogs with toxoplasmosis often also have other diseases, such as canine distemper. A blood test or tissue sample can be used to diagnose the infection. Various drugs are recommended for treatment.

Parasitic Diseases

Verminous myelitis is inflammation of the spinal cord caused by a parasite. The most common such parasite in dogs is a roundworm called Baylisascaris procy-onis. Signs of spinal cord inflammation strike suddenly and severely, often affecting one side of the body more than the other, and may progressively worsen over time. This condition is difficult to diagnose except by examination of tissues after death. Drug treatment can be beneficial, but a full recovery is uncertain.

Inflammatory Diseases of Unknown Cause

Granulomatous meningoencephalomyelitis is an inflammatory disease of the central nervous system that occurs in dogs worldwide. The cause is unknown, but it may be a viral infection. There are 2 different forms of the disease that have different effects within the body, but the signs are similar, and often include neck pain and partial paralysis in all 4 legs. Adult dogs of any breed can be affected, but female small-breed dogs, especially Poodles, are at highest risk. Signs can occur suddenly or slowly worsen over several months. An accurate diagnosis requires cerebrospinal fluid analysis. Dogs often improve temporarily with drug treatment, but the longterm outlook is guarded.

Tumors

Tumors that affect the spinal column and cord in dogs include cancers of the bone, connective tissue, meninges, and nerve sheath, in addition to metastatic cancers, which are cancers that have spread from other parts of the body. A specific tumor called a nephroblastoma can affect young dogs (from 5 to 36 months of age), with German Shepherds affected most commonly. This tumor is frequently in the middle or lower back, causing progressively worsening partial paralysis in the hind legs. Imaging (including x-rays, myelography, computed tomography, magnetic resonance imaging) and surgical biopsy are used to identify and confirm a diagnosis of spinal cancer. Surgery is possible in some cases.

Injury and Trauma

Spinal cord injuries usually occur as a result of a spinal fracture or dislocation. Common causes in dogs include automobile accidents, bite wounds, and gunshot wounds. The injury not only causes initial damage to the spinal cord, but also causes secondary damage from swelling, bleeding, destruction of the nerve sheath, and tissue decay. Signs of spinal trauma typically have a sudden and severe onset, and may progressively worsen. Severe spinal cord injury to the middle or lower back may cause a rigid paralysis, or a limp paralysis that spreads to the entire body over several days and leads to death from respiratory paralysis. Fractured or dislocated vertebrae can often be seen on x‑rays. Drug treatment can be helpful if started within the first few hours of injury. Animals with mild neurologic signs from injury often recover after 4 to 6 weeks of cage rest. Surgery is necessary for some types of injuries that cause severe neurologic signs. In dogs that have lost the ability to feel pain at locations below the spinal injury, the outlook for recovery is poor.

Poisoning and Toxic Disorders

Delayed organophosphate intoxication can be seen after ingestion or skin contact with insecticides or pesticides that contain organophosphates. In addition to the signs of severe exposure, delayed paralysis can develop 1 to 4 weeks after exposure. Partial paralysis of the hind legs worsens progressively, and occasionally all 4 legs become paralyzed. A veterinarian will need a history of the dog’s possible chemical exposure to make the correct diagnosis. The outlook for recovery is poor for animals with severe signs.

Tetanus is caused by toxins produced by Clostridium tetani bacteria that usually enter the body at the site of a wound. Dogs are fairly resistant to tetanus, but cases do sometimes occur. Signs usually develop within 5 to 10 days of infection and include muscle stiffness and rigid leg extension, inability to swallow, protruding eyelids, and locking of the jowl and facial muscles. In severe cases, the animal may be unable to stand as a result of muscle spasms. Treatment consists of wound care, antibiotics to kill any remaining organisms, and tetanus antitoxin. In mild cases, a dog may recover completely with early treatment. In severe cases, death may occur due to respiratory paralysis.

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