Nonsurgical spinal cord diseases: It is not always a disk (Proceedings)

Fibrocartilagenous Emboli (FCE)

Fibrocartilagenous embolus(i) is an acute spinal cord infarction(s) caused by microscopic spinal vessel occlusion by material histologically resembling the intervertebral disk (nucleus pulposus). It has been infrequently reported in horses, pigs, a cat and possibly in neonatal lambs. Fibrocartilagenous emboli is more likely to occur in large or giant breed dogs. The most commonly recognized breeds are the Labrador retriever, German shepherd, Golden retriever, Doberman pinscher, Great Dane and mixed breed. These large breeds may be over-represented based on breed popularity. Smaller breeds such as the Miniature Schnauzer, Shetland sheepdog, Wirehair fox terrier have also been reported. The emboli are histologically identical to the nucleus pulposus of the intervertebral disk. The distribution of the spinal artery branches are irregular and unpredictable in the dog, especially in the thoracolumbar spinal cord. Many dogs may have as few as 2 total branches to cord segments T10-L6, resulting in severe susceptibility to ischemic injury. A high percentage of unilateral central artery distribution may account for the often asymmetric clinical signs. While there is a great anastomotic extravertebral vascular network, the intrinsic spinal cord arteries are an end flow system. All of these factors may contribute to the pathophysiology of FCE. The emboli can be present in arterial, venous vasculature or both. There appears to be no correlation of severity or extent of clinical signs to the type of vasculature occluded.

Affected dogs are typically large or giant breed and middle-aged. The average age is 3-7 years (range 3 months to >15 years). There is no sex predilection from multiple reports. Signs are acute or peracute with clinical signs developing over minutes to hours, but usually stabilizing by 24 hours. Neurological dysfunction will be referable to the distribution of the spinal arteries affected and the extent of the injury. The signs may be very mild to severe with paralysis (hemi-, para- or tetraplegia). There may be a predilection for the cervical and lumbar intumescences resulting lower motor neuron signs. The presence of symmetry does not preclude a diagnosis. Animals with very extensive embolic events may develop ascending/descending myelomalacia. Although clients may report the dog crying out prior to onset of signs, the disease is not considered painful. The initial episode of discomfort felt by the dog may be related to vascular pain because the spinal cord does not possess pain receptors.

Antemortem diagnosis of FCE is typically a diagnosis of exclusion of other diseases. FCE should be considered a primary differential for any dog of correct signalment with acute onset of nonpainful cervicothoracic, thoracolumbar or lumbosacral syndrome, with or without symmetry of neurologic signs.

Spinal radiographs may reveal evidence of chronic degenerative disk disease (narrowed disk spaces) and/or spondylosis. Myelogram may reveal a swollen spinal cord if performed early or be normal if performed in the subacute period. Cerebrospinal fluid is not typically helpful in the diagnosis. Analysis may reveal normal fluid, albuminocytologic dissociation (high protein, normal cell count), high protein with mononuclear pleocytosis, or high protein with neutrophilic pleocytosis. The CSF analysis will be influenced by the location of the tap in relationship to the injury, the time between acquiring the tap and the onset of signs, and prior treatment (steroids).

Definitive diagnosis is only made by histopathology which requires necropsy.

Treatment is generally supportive with good hygiene, urinary bladder management, physical therapy, and good padding for the non-ambulatory dog. There has been no proven benefit to use of corticosteroids. However, as with any spinal cord trauma, ischemia will set up a series of biochemical events resulting in release of inflammatory mediators and oxygen free radical production that will promote injury. The author will usually use glucocorticoids if the animal is seen early in the course of the disease. There is probably no good reason to initiate therapy with these potent steroids after 72 hours.

Prognosis is dependent on the severity/extent of the injury, the lesion localization and presence of deep pain response. Loss of deep pain and lower motor neuron signs are the most significant indicators of poor prognosis. Lower motor neuron signs are less likely to recover because the metabolic needs of gray matter are higher and nerve cell bodies are much less likely to recover from injury than axons. Asymmetric paraparesis may leave a dog with three functional limbs, therefore resulting in an inherently better prognosis. Most dogs whom are going to improve significantly will begin to show recovery in the first 7-14 days. Many dogs are left with permanent dysfunction but learn to compensate and become functional pets. Improvement is probably related to resolution of hemorrhage and edema, recovery of neural tissue from sublethal injury, and presence or development of collateral circulation.

Diskospondylitis

Discospondylitis is typically defined as an infection (bacterial, occasionally fungal) of an intervertebral disc and its adjacent vertebral end plates. Hematogenous spread of organisms to the vertebrae or the intervertebral discs is thought to be the most common pathogenesis. Infection is though to begin in the end plate zone of the vertebrae where bacteria can then diffuse across the cartilaginous end plate into the intervertebral disc where the infection can further disseminate to adjacent vertebrae. The infection may originate from bacteria associated with cystitis, vegetative endocarditis, dental disease, and integumentary sources. Prostatitis or orchitis caused by Brucella canis can also serve as a source of infection. In cases of fungal discospondylitis, the animals usually present with a disseminated form of the disease.

Foreign bodies, such as grass awns, have also been implicated as a source of vertebral infection. Several theories have been suggested to explain the awns' migration to the intervertebral disk. Ingested awns may migrate through the bowel wall, up the mesentery to its ventral attachment to the epaxial muscles and vertebral column. It is also theorized that inhaled plant material could migrate through the lungs to the diaphragm and lodge at the crural insertion on the vertebrae. Awns may also simply penetrate the skin and migrate through abdominal or epaxial musculature to the vertebral column.

Kornegay et al. (1980) found that large active dogs are most commonly affected, with males outnumbering females almost 2:1. German Shepherd dogs and Great Danes have been over-represented in a number of studies while reports in cats are rare. Most dogs are young to middle-aged at the time of diagnosis, but animals of any age can be affected. Reports in the literature range from 5 months to 13 years of age at the time of diagnosis.

Most dogs present for spinal pain over the region of infection and recurrent fever with variable degrees of neurological impairment such as paresis. Neurological impairment is not required to suspect this differential, but these animal typically appear systemically ill. If neurological deficits are present they tend to be progressive. Other common presenting signs include depression, stilted gait, reluctance to walk, weight loss, abdominal pain, and pyrexia. Any vertebrae or disc may be affected, but the caudal cervical (C6-C7), midthoracic (T5-T6), thoracolumbar (T13-L1), and lumbosacral (L7-S1) are areas of predilection. Multiple disc spaces can be involved, although, adjacent disc involvement is more common than multifocal infections (Robinett, 1996). Complete blood count as well as chemistry profile are usually within normal limits, although leukocytosis with a left shift is occasionally seen.

A clinical diagnosis of discospondylitis is commonly based on the combination of radiographic changes, positive blood and/or urine cultures, or serologic evidence of infection with Brucella canis. Traditional radiographic findings in cases of discospondylitis include: collapse of the intervertebral disc space, lysis of the vertebral end plates, sclerosis, and spondylitis. It can take up to 2-4 weeks from the time of infection to see the radiographic abnormalities. Bone scintigraphy, however, can show increased activity by 3 days post infection, although false negative results are occasionally seen.

All dogs with radiographic evidence of discospondylitis should be screened for Brucella canis using the rapid slide agglutination test, the tube agglutination test, or the agar gel immunodiffusion test. Owners of dogs that test positive for Brucellosis, should be warned of the public health risks as numerous cases of human Brucellosis due to B. canis have been reported.

Blood and urine should be cultured to look for a specific etiologic agent. Blood cultures have been reported as positive in 45% to 75% of cases depending on the source. Urine cultures have been positive in about 40% of affected dogs. If bone cultures are done, they usually correspond to isolates from blood and urine and typically have similar sensitivity patterns. Fisher et al. (1997) performed 12 fluoroscopically guided percutaneous disk aspirations in dogs with discospondylitis and obtained positive cultures in 75% of the cases with no adverse clinical sequelae. Cerebrospinal fluid analysis is not indicated but if performed, is generally within normal limits, with the exception of occasional mild protein elevation.

Discospondylitis is diagnosed by survey radiographs, CT, and MRI. MRI criteria including narrowed IV disc space, loss of the end plate clarity signifying cortical bone erosion, decreased signal on T1 weighted images and increased signal on T2 weighted images of the bone marrow and end plates of affected vertebrae. Abnormalities are also typically noted in paraspinous and epidural soft tissues. In early cases before radiographic changes are identified, nuclear scintigraphy can help support a diagnosis but is not specific for diskospondylitis.

The factors in choosing a therapeutic regimen include: 1. The degree of neurological dysfunction, 2. Results of B. canis titer, 3. Culture results from blood and urine, 4. Multiplicity of lesions, and 5. Surgical accessibility of the lesions. In dogs with little or no neurological dysfunction, long term antibiotics based on culture and sensitivity results and cage rest are usually adequate. If an etiologic agent is not identified, it is assumed to be a coagulase-positive Staphylococcus species. A β-lactamase resistant and preferably bactericidal antibiotic should be chosen. Cloxacillin, dicloxacillin, and oxacillin are recommended first choice antibiotics. Most dogs treated with the appropriate antibiotic respond almost immediately and do not suffer a relapse. Antibiotic therapy should be carried out a minimum four to six weeks and may need to be carried out much longer. Dogs that fail to respond within five to seven days should be reassessed. Nonsteroidal anti-inflammatory medications, opioid medications and/or Tramadol are beneficial to control bone pain.

If Aspergillosis is diagnosed, a combination of ketoconazole and amphotericin B may be used for at least six to eight weeks. Itraconazole, fluconazole, and vinbunazole may also be considered. In cases of Brucellosis, it is recommended that males be neutered because there is some evidence that it can be difficult to clear infections from the prostate gland. A combination of minocycline and dihydrostreptomycin administered for two to three weeks has been reported as being the most successful treatment protocol. This may need to be repeated two or more times to get resolution of the infection.

Surgery is indicated in animals with solitary, accessible lesions that have marked neurological deficits and are not responding to conservative therapy. Spinal cord decompression, bone samples for culture and sensitivity, curettage of intradiscal lesions, and spinal stabilization, if indicated, are performed. Decompressive surgery is accomplished by either dorsal laminectomy or hemilaminectomy.

The resolution of radiographic lesions can be used as a guide to therapy. In cases with extensive bony proliferation, it may be prudent to continue antibiotic therapy for four to six weeks past radiographic resolution of bone lysis.

Prognosis is dependant on neurological examination on presentation and response to initial medical management. Patients who present with spinal hyperesthesia only or accompanied by paraparesis and respond well to initial medical therapy have a good to excellent prognosis. Patients with more severe neurological deficits especially with evidence of an extradural lesion or spinal instability have a guarded to poor prognosis whether or not surgical decompression and/or vertebral stabilization are utilized.

Degenerative Myelopathy (DM)

Degenerative myelopathy is a chronic, progressive thoracolumbar leukomyelopathy that has been well-described in middle-aged to older German shepherd dogs. Most dogs are >5 years of age, but there are reports in dogs as young as 6-7 months. A genetic basis is presumed in German shepherd dogs. A similar myelopathy has been seen in Siberian huskies. Chesapeake Bay retrievers may be another breed in which this disease is more common. The disease has been reported in Kerry Blue terriers, rough coated collies and a domestic shorthair cat. The author has seen similar syndromes in a collie, two Irish setters, several Boxers, a Pembroke Welsh Corgi and an Australian shepherd. Whether these cases represent the same underlying pathophysiology as the German shepherd dog is not known.

Lesions of DM are a diffuse leukomyelopathy of all thoracolumbar funiculi. Changes include degeneration with vacuoles and ballooning and fragmentation of myelinated axons. Phagocytosis of cellular material and astrocytosis is also recognized. There are no significant gray matter lesions (poliomyelopathy). The lesions are bilateral but not always symmetrical. There is no selective tract involvement but the lesions are discontinuous. Changes may be seen in the cervical spinal funiculi but thoracic limbs are usually spared until very late in the course of the disease. Thoracic limb involvement usually occurs after the animals lose motor function to the pelvic limbs.

The underlying cause of DM is not truly known. The clinical signs of DM are insidious and progressive. Some dogs may have a waxing and waning course in the progression. Although the course of the disease is reported as 6 months to 1 year, the rate and length of the course may be longer and is very variable between patients. Clients usually notice first stumbling, ataxia and conscious proprioceptive deficits (scuffing the toes, wear of dorsum of nails) of the pelvic limbs. The author has seen several dogs that are severely ataxic but have only minimal delay in conscious proprioception when testing postural reactions. Dogs will progress to paraparesis and eventually a non-ambulatory status (severe paraparesis or paraplegia). Superficial and deep pain sensation is retained. Clients will often perceive the dog is painful simply on the gait abnormalities but DM is not associated with pain. The dogs will develop dysmetria. The reflexes reflect a T3-L3 (thoracolumbar) lesion localization with normal-to-increased pelvic limb reflexes. Some dogs (15%) may actually have decreased patellar reflexes which is not consistent with thoracolumbar syndrome. Nerve root involvement (radiculopathy) of the roots supplying the femoral nerve has been documented and may explain the finding of patellar hyporeflexia. There may be some asymmetry to the signs but both pelvic limbs are affected. The thoracic limbs are normal until very late. Thoracic limb involvement is usually only seen in dogs that are maintained non-ambulatory for some time. Urinary and fecal incontinence may develop as well. Disuse atrophy of the pelvic limbs may develop. Some dogs will have significant paraspinal muscle atrophy in the thoracolumbar area.

DM is a diagnosis of exclusion. Myelography does NOT diagnose degenerative myelopathy. Signalment and history (insidiously progressive non-painful paraparesis with ataxia) are the keys to diagnosis. The difficulty with diagnosis of DM is the other concurrent problems that German shepherds might have. Some dogs may have chronic type II disk disease, spinal arthritis, hip dysplasia and lumbosacral degenerative disease as well as DM. Some dogs may have all of these problems. More than one orthopedic surgeon has performed a total hip replacement only to have the dog development signs of DM later. Myelogram reveals no compressive lesion or swelling. Some dogs have a very subtle-to-mild disk herniation that is not severe enough to account for the clinical signs. CSF analysis is usually normal but protein may be elevated. The author has found that these dogs can be much worse transiently following myelography. Occasionally, these dogs remain permanently deteriorated. This deterioration may be because of neurologic decompensation following anesthesia, manipulation during radiographic procedures that exacerbates other problems and mild inflammatory responses to the myelographic material. Myelography should not be a whimsical suggestion but is required to rule out other diseases with a possible surgical therapy (disk disease, tumor).

Many neurologists feel there is no consistently effective treatment. The internet web site on DM proposes a conglomeration of holistic and medical therapies (anti-oxidant and membrane stabilizer compounding, gingko, ginseng, aminocaproic acid, n-acetylcysteine,etc.) based on recommended therapy for human multiple sclerosis. The web site claim is that 80% of dogs improve. There is no published data and the claim is not supported with objective proof (serial neurological examinations). Many neurologists have not found these therapies to be effective and do not necessarily recommend them. While there is probably no harm in most of the recommended therapies and some may have a basis for other possible abnormalities in DM, the suggested regimen may run as much as $150-200/month. It is difficult to strongly advocate this therapy with no scientific proof of efficacy. The pros/cons and costs can be discussed with the client. What can be suggested is mild to moderate exercise (walking, swimming) to maintain muscle tone/mass, good nutrition, good hygiene , and the addition of a good pet vitamin and vitamin E (200-1000 IU/day). Clients may opt for the K-9 cart rather than euthanasia when the dog becomes non-ambulatory.