SPINAL CORD DISEASE IN DOGS PART TWO: MOST LIKELY CAUSES

Vet Times The website for the veterinary profession https://www.vettimes.co.uk SPINAL CORD DISEASE IN DOGS PART TWO: MOST LIKELY CAUSES Author : RITA GONÇALVES Categories : Vets Date : April 7, 2014 RITA GONÇALVES in the second part of her article, discusses the reasons why this neurological disorder occurs in canines, the use of imaging to aid diagnosis and treatment options SPINAL cord disease is one of the most common reasons for neurology referral. When assessing these dogs, it is important to perform a thorough physical and neurological examination to localise the origin of the problem, to guide the investigation process as described in part one (VT 44.09). Taking a good history is essential as discussed previously. Most importantly, determining the speed of onset (acute versus chronic) and the presence or absence of pain, as well as establishing if the disease is progressive or not, will be crucial in elaborating this list. To be thorough and consistent, the author likes to follow the vitamin D differential diagnoses list. To make it easier to narrow these down, Table 1 divides them according to whether they cause pain and are progressive. Vascular conditions Ischaemic myelopathy in dogs is most commonly associated with a fibrocartilaginous embolism (FCE). In these cases, a small piece of intervertebral disc penetrates and blocks a spinal blood vessel and results in spinal cord ischaemia. Dogs present with acute onset of neurological deficits (often very lateralised) that are not associated with pain and do not get worse with time. Diagnosis requires MRI and myelography can be used to rule other problems out (Figure 1a and 1b). 1 / 22

Treatment mainly involves physiotherapy and hydrotherapy and, occasionally, management of urinary dysfunction in the more affected cases. There is no need for surgery as the injury is due to ischaemic damage to the spinal cord and only requires time for healing to occur. Inflammatory conditions Immune-mediated causes for spinal cord disease are most common, but infectious causes are also possible. For example, discospondylitis, which is an infection of the intervertebral disc space and adjacent vertebrae, typically causes severe spinal pain. Diagnosis is achieved on radiography (remember, it may take two to four weeks for changes to be identifiable with this imaging modality) or MRI if felt this is appropriate in the early stages (Figure 2a). When confirmed, a cause for the infection should be looked for; blood cultures are positive in up to 75 per cent of cases and urine culture in up to 50 per cent. Treatment with antibiotics should be continued for six to eight weeks and initial pain relief is appropriate in most cases. The most common cause of spinal immune-mediated disease is meningomyelitis of unknown origin. In this group of diseases inflammation of the spinal cord occurs. They mostly affect the brain, or both brain and spinal cord, but sometimes only affect the spinal cord. They most commonly present as acute, progressive and usually painful (although not always) myelopathies. It is often confused with intervertebral disc disease as most commonly affect young to middle- aged small breed dogs. Diagnosis is usually made with MRI and, most importantly, analysis of the cerebrospinal fluid (CSF) to document the inflammation. Treatment is made with immunosuppressive drugs (corticosteroids), but supportive care and physiotherapy is essential in the initial stages. Traumatic conditions Traumatic injury may cause different types of lesions that will present in different ways and require very different treatment. The two most common results of spinal trauma are fractures and luxations usually associated with instability, which results in pain and progression of the clinical signs until stabilisation is performed and traumatic disc extrusions, which are mainly associated with spinal cord contusion without compression or significant instability, so is usually not associated with pain and with neurological deficits that improve with time without any treatment. Cases resulting in fractures and luxations typically happen with more significant trauma, such as RTAs or falls from height, and are associated with pain and progression of the clinical signs. It is important to start by performing radiographs of the spine (always orthogonal views) and look for other possible trauma with radiographs of the entire spine, chest and abdomen. 2 / 22

It is essential to determine the prognosis at presentation: spinal fractures in the absence of pain perception carry a poor prognosis, with it being usually thought a less than five per cent likelihood of walking again. Treatment can be conservative, such as splinting/cage rest don t forget pain management, or surgical if there is instability. Those cases where the traumatic injury does not result in fracture or luxation, but put the intervertebral disc under significant pressure, result in a traumatic disc extrusion also called high velocity/low volume disc or acute non-compressive nucleus pulposus extrusion (ANNPE). When the disc is healthy (hydrated and not significantly degenerated), there is extrusion of a hydrated disc that hits the spinal cord at high speed and causes mainly spinal cord contusion with minimal associated compression. Often associated with mild trauma (often just exuberant exercise), dogs typically present with acute onset of neurological deficits that are less commonly associated with pain and that do not get worse with time (very similar presentation to FCEs). Diagnosis requires MRI (Figure 1c and 1d), and radiographs and myelography can be used to rule other problems out. Treatment mainly involves physiotherapy and hydrotherapy and, occasionally, management of urinary dysfunction in more affected cases. Surgery is not needed as there is no significant compression of the spinal cord and the injury is mainly contusive damage only requiring time to heal. Anomalous conditions Many anomalous conditions affect the spine and spinal cord, such as block, transitional or hemivertebrae, but they do not always result in neurological deficits only if they cause significant compression of the spinal cord or nerve roots. It is important, therefore, to couple imaging findings, such as anomalous vertebrae on a radiograph, with neurological deficits that localise to that region of the spine. One of the most common malformations associated with significant clinical signs is atlantoaxial instability. This usually affects young dogs that present with acute or waxing and waning episodes of neck pain, with or without ataxia and tetraparesis. It occurs from failure of ligamentous support, usually associated with aplasia/hypoplasia of the dens in toy breeds. Diagnosis is made through radiographs of the cervical spine: the lateral view shows an increased space between the dorsal lamina of the atlas (C1) and the dorsal spinous process of the axis (C2), and the ventrodorsal view will allow assessment of the presence and size of the dens. Treatment can be conservative with splinting for six to 10 weeks or involve surgical stabilisation. Neoplastic conditions 3 / 22

Dogs with tumours of the spine and spinal cord characteristically present with slow onset, progressive and usually painful (except in intramedullary lesions) signs of spinal cord dysfunction ( ). Diagnosis can be achieved through spinal radiographs, CT myelography or MRI. Figure 3a Treatment options include surgery, chemotherapy or, rarely, radiotherapy, but most often palliative treatment with analgesia is used. Degenerative conditions There are many degenerative conditions that result in spinal cord dysfunction. They can be associated with degeneration of the intervertebral disc, joints (articular facets of the spine), spinal cord itself and so on. Degenerative intervertebral disc disease type I Degenerative intervertebral disc disease type I (extrusion) occurs when there is herniation of the nucleus pulposus (middle of the disc) through the annular fibres (outer thicker layer of the disc) with extrusion of the nuclear material into the spinal canal. Onset of clinical signs is usually acute and often progressive. Diagnosis can be achieved through myelography (with or without CT) or MRI ( Figure 4a and 4b). Treatment is conservative in many cases, but often involves surgery when the neurological deficits are more severe, in those where conservative treatment has been attempted, but was unsuccessful or in cases associated with severe pain. Degenerative intervertebral disc disease type II Degenerative intervertebral disc disease type II (protrusion) occurs when there is protrusion of the annulus caused by shifting of central nuclear material there is a bulge of the disc that compresses the spinal cord. Protrusions are more common in older, non-chondrodystrophic dogs, which present with chronic, slowly progressive signs, which may or may not include spinal pain. The neurological deficits are often less severe than with type I disease. The diagnosis can be achieved through myelography (with or without CT) or MRI (Figure 4c and 4d). Treatment is conservative in milder cases, but surgery is indicated when the neurological deficits are more severe. Caudal cervical spondylomyelopathy Caudal cervical spondylomyelopathy (wobbler) is typically seen in large breed dogs presenting with progressive ataxia, tetraparesis and sometimes neck pain. The clinical signs are usually worse in the pelvic limbs, with a short, stilted gait in the thoracic limbs. It can result from a combination of 4 / 22

problems, but most commonly associated with intervertebral disc protrusion in the caudal cervical spine. Diagnosis can be achieved through myelography (with or without CT) or MRI. Treatment can be conservative in mild cases, but often involves surgery (decompression or distractionstabilisation). Lumbosacral disease In the lumbosacral region the vertebral canal contains only the cauda equina as the spinal cord ends at L6 in most dogs and L7 in cats and small dogs. Therefore, the clinical signs are usually related to pain (often manifested through lameness and reluctance to jump and exercise) and mild weakness of the pelvic limbs. It is most commonly caused by intervertebral disc protrusion at the lumbosacral region, but can also be due to other problems in this region. Diagnosis can be confusing as the clinical signs are often vague and should take into account a combination of the results of the physical, neurological and orthopaedic examinations, as well as those from MRI. It is important to evaluate the nerve roots at this level so myelography is not indicated for these cases. Treatment can be conservative in milder cases, otherwise it involves surgery (decompression or distraction-stabilisation). Degenerative myelopathy Degenerative myelopathy (DM) is a degenerative disease that affects older dogs (usually around eight to 10 years of age), causing chronic onset weakness of the pelvic limbs that slowly progresses over six to 12 months until complete loss of movement. This condition is not associated with pain. Keep in mind many of the breeds that have this condition (such as German shepherd dogs, corgis and boxers) are also commonly affected with chronic intervertebral disc disease, which can present very similarly. Myelography and MRI are normal in these dogs; analysis of the CSF often shows increases in protein levels. There is a genetic test for the mutation (SOD1) associated with DM, but unfortunately a homozygous positive result does not mean the dog has, or will, develop the disease (a negative test though makes it very unlikely). There is no specific treatment available for this condition, but physiotherapy and hydrotherapy help maintain muscle strength and are associated with longer survival. Treatment options Conservative treatment mainly involves rest and appropriate analgesia (NSAIDs, paracetamol and gabapentin are most commonly used). In many cases, physiotherapy and hydrotherapy are indicated, either in cases where there is no compression (FCE, ANNPE), but also post-surgery to improve and speed up recovery. 5 / 22

In cases where there is compression of the neural tissue, surgery is often indicated (for example, cases with intervertebral disc disease or any other compressive material close to the spinal cord) when these are not improving with conservative treatment or are causing severe deficits. In cases where there is instability, stabilisation of fractures or luxations is often necessary. Note that gabapentin is not licensed for veterinary use. Figure 1. MRIs of non-compressive spinal cord injuries. A (sagittal T2-WI) and B (transverse T2-WI) are MRIs of a dog with a fibrocartilagenous embolism. C (sagittal T2-WI) and D (transverse T2-WI) are MRIs of a dog with a traumatic disc extrusion. It appears similar to the above, but most changes are localised just above the intervertebral disc space. 6 / 22

Figure 1. MRIs of non-compressive spinal cord injuries. A (sagittal T2-WI) and B (transverse 7 / 22

T2-WI) are MRIs of a dog with a fibrocartilagenous embolism. C (sagittal T2-WI) and D (transverse T2-WI) are MRIs of a dog with a traumatic disc extrusion. It appears similar to the above, but most changes are localised just above the intervertebral disc space. Figure 1. MRIs of non-compressive spinal cord injuries. A (sagittal T2-WI) and B (transverse T2-WI) are MRIs of a dog with a fibrocartilagenous embolism. C (sagittal T2-WI) and D (transverse T2-WI) are MRIs of a dog with a traumatic disc extrusion. It appears similar to the above, but most changes are localised just above the intervertebral disc space. 8 / 22

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Figure 1. MRIs of non-compressive spinal cord injuries. A (sagittal T2-WI) and B (transverse T2-WI) are MRIs of a dog with a fibrocartilagenous embolism. C (sagittal T2-WI) and D (transverse T2-WI) are MRIs of a dog with a traumatic disc extrusion. It appears similar to the above, but most changes are localised just above the intervertebral disc space. Figure 2. Lateral radiograph (A) and sagittal T1-WI image (B) of two dogs with discospondylitis. Note the narrowing of the intervertebral disc space, and irregularity and lysis of the endplates, as well as development of spondylosis. 10 / 22

Figure 2. Lateral radiograph (A) and sagittal T1-WI image (B) of two dogs with discospondylitis. Note the narrowing of the intervertebral disc space, and irregularity and lysis of the endplates, as well as development of spondylosis. 11 / 22

Figure 3. Spinal neoplasia. A: normal spinal cord. B: extradural neoplasia compressing the spinal cord (soft tissue sarcoma). C: intradural extramedullary neoplasia (meningioma). D: intradural intramedullary neoplasia (glioma). 12 / 22

Figure 4. Degenerative intervertebral disc disease (IVDD). A (sagittal T2-WI) and B (transverse T2-WI) are MRIs of a dog with IVDD type I. Note the disc material has extruded to the spinal canal and is causing significant compression of the spinal cord. C (sagittal T2-WI) and D (transverse T2-WI) are MRIs of a dog with IVDD type II. Note the disc is bulging as a whole and causing milder compression of the spinal cord. 16 / 22

and is causing significant compression of the spinal cord. C (sagittal T2-WI) and D (transverse T2-WI) are MRIs of a dog with IVDD type II. Note the disc is bulging as a whole and causing milder compression of the spinal cord. Figure 4. Degenerative intervertebral disc disease (IVDD). A (sagittal T2-WI) and B (transverse T2-WI) are MRIs of a dog with IVDD type I. Note the disc material has extruded to the spinal canal and is causing significant compression of the spinal cord. C (sagittal T2-WI) and D (transverse T2-WI) are MRIs of a dog with IVDD type II. Note the disc is bulging as a whole and causing milder compression of the spinal cord. 18 / 22

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