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Ascending and descending (haemorrhagic) myelomalacia (ADHMM) is a severe complication of spinal cord injury including disc herniation. The pathophysiology of this phenomenon is not completely understood. Myelomalacia is defined as gross softening of the spinal cord with hemorrhagic necrosis and liquefaction of the spinal cord tissue. ADHMM should be suspected in dogs that have an ascending loss of the cutaneous trunci reflex. Other signs include loss of nociception caudal to the lesion, ascending and descending flaccidity and areflexia, tetraplegia, hyperthermia, and respiratory distress.

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Clinical Characteristics of Dogs with Progressive Myelomalacia (PMM) Following Acute Intervertebral Disc Extrusion

This paper aims to describe the onset and progression of clinical signs of PMM in 51 dogs.

Onset was seen up to 5 days after presentation wiith half of dogs developing signs within 48 hrs. Progression to time of death ranged from 1-13 days with nearly half euthanized within 3 days. Mid-to-caudal lumbar discs might be associated with an increased risk of PMM.

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Endothelin-1 Immunoreactivity and its Association with Intramedullary Hemorrhage and Myelomalacia in Naturally Occurring Disk Extrusion in Dogs

This study aims to investigate the immunoreactivity of endothelin-1 (ET-1) in the uninjured and injured spinal cord of dogs and its potential association with intramedullary hemorrhage and extension of myelomalacia and finds that enhanced ET-1 immunoreactivity over multiple spinal cord segments after disc extrusion might play a role in the pathogenesis of ADMM.

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Single-shot turbo spin echo pulse sequence findings in dogs with and without progressive myelomalacia

Length of cerebrospinal fluid attenuation was recorded as a ratio to the length of the L2 vertebral body in SSTSE and T2W sequences. Length of intramedullary spinal cord hyperintensity was recorded as a ratio to the length of the L2 vertebral body in T2W sequences. A total of 21 dogs were included (five in the progressive myelomalacia group and 16 in the control group). The mean CSF:L2SSTSE attenuation value was significantly higher in dogs that developed progressive myelomalacia. A cut off ratio of attenuation >7.4 provided optimal differentiation between groups in this study.

MRI features can help to confirm a diagnosis of progressive myelomalacia

MRI features such as length of T2W hyperintense spinal cord change and HASTE signal loss were significantly associated with clinically evident progressive myelomalacia (PMM), however, there was no significant difference between groups when analysis was restricted to dogs not yet showing clinical signs of PMM. A segment of total loss of contrast enhancement in the venous sinus and meninges, a feature not previously described, was more common in the PMM group than in other dogs presenting paraplegic and loss of nociception. Importantly, although MRI features can support the diagnosis in dogs with clinical evidence of PMM, and absence of these features is supportive of the absence of the disease at the time of imaging, imaging features may not reliably differentiate dogs who will develop PMM in the future from other dogs with severe deficits following IVDE.

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Prevalence and Risk Factors for Presumptive Ascending/Descending Myelomalacia (ADMM) in Dogs after Thoracolumbar Intervertebral Disk Herniation

 This study investigated the prevalence and risk factors for ADMM in 652 non-ambulatory dogs with surgically treated TL-IVDH.

Thirteen dogs developed ADMM, with an overall prevalence of 2.0%. The prevalence of ADMM was 0% in dogs with neurological signs graded 1 or 2. Age (<5.8 years), neurological status (grade 5), site of disk herniation (L5-L6), duration of clinical signs before becoming nonambulatory (<24 hours), detection of intramedullary T2-weighted (T2W) hyperintensity, and a T2 length ratio >4.57 were significant risk factors.

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Risk factors associated with progressive myelomalacia (PMM) in dogs with complete sensorimotor loss following intervertebral disc extrusion: a retrospective case-control study

The objective of this retrospective case-control study was to identify risk factors for PMM by comparing dogs with complete sensorimotor loss following IVDE that did and did not develop the disease after surgery and found that dogs with lumbar intumescence IVDE are at increased risk of PMM.

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