Magnetic resonance imaging characteristics of atlanto-axial subluxation in 42 dogs: Analysis of joint cavity size, subluxation distance, and craniocervical junction anomalies

Background

Atlanto-axial (AA) subluxation can be a complex syndrome in dogs. Accurate identification and assessment of this condition are key to providing treatment and resolution.

Aim

The purpose of this retrospective study was to describe the magnetic resonance imaging (MRI) characteristics of AA subluxation and associated neurologic deficits.

Methods

A multicenter review of dogs with a diagnosis of AA subluxation was conducted, evaluating signalment, neurologic grade, duration of signs, and MRI characteristics. MRI characteristics included degree of spinal cord compression and joint subluxation, integrity of odontoid ligaments, presence of a dens, spinal cord signal intensity, and presence of syringohydromyelia, hydrocephalus, and Chiari-like malformation. A control population with normal AA joints was also evaluated. MR images of 42 dogs with AA subluxation were compared to 26 age and breed-matched control dogs.

Results

Affected dogs had a median age of 27 months and a median weight of 2.7 kg, and the most commonly affected breed was the Yorkshire terrier (47.5%). Spinal cord signal hyperintensity, increased AA joint size, and cross-sectional cord compression at the level of the dens and mid-body C2 were associated with AA subluxation. No associations were found between cord compression, the appearance of the dens, or cord signal intensity and neurologic grade. Affected dogs did not have a higher incidence of Chiari-like malformation, syringohydromyelia, or hydrocephalus than control dogs, and their neurologic grade was not associated with MRI findings. Lack of dens and/or odontoid ligaments was associated with larger subluxations.

Conclusion

Dogs with clinical signs of AA subluxation were significantly more likely to have intramedullary hyperintensity at the level of compression ( p = 0.0004), an increased AA joint cavity size ( p = 0.0005), and increased spinal cord compression at the level of dens and mid-body C2 (p ≤ 0.05). The authors suggest an AA joint cavity size >1.4 mm and a subluxation distance >2.5 mm as cutoffs for MRI diagnosis of AA subluxation in dogs. No differences were noted between dogs with AA subluxation and control dogs regarding syringohydromyelia, hydrocephalus, and Chiari-like malformation.

Continuous rate infusion of midazolam as emergent treatment for seizures in dogs

Background

Midazolam delivered by continuous rate infusion (CRI) might be effective in dogs with cluster seizures (CS) or status epilepticus (SE).

Objective

To describe the use and safety of midazolam CRI in dogs with CS or SE.

Animals

One‐hundred six client‐owned dogs presenting to a veterinary teaching hospital with CS or SE.

Methods

Retrospective review of medical records for dogs with CS or SE treated with a midazolam CRI.

Results

Seventy‐nine dogs presented with CS and 27 dogs had SE. Seizure control was achieved in 82/106 dogs (77.4%) receiving a midazolam CRI. The median dose associated with seizure control was 0.3 mg/kg/h (range, 0.1‐2.5 mg/kg/h). The median duration of CRI was 25 hours (range, 2‐96 hours). Seizures were controlled in 34/40 dogs (85%) with idiopathic epilepsy, 32/43 dogs (74%) with structural epilepsy, 12/16 dogs (75%) with unknown epilepsy, and 4/7 dogs (57%) with reactive seizures (P = .20). Seizure control was achieved in 81% of dogs with CS and 67% in dogs with SE (P = .18). Dogs with idiopathic/unknown epilepsy were more likely to survive than those with structural epilepsy (87% vs 63%, P = .009). Adverse effects were reported in 24 dogs (22.6%) and were mild in all cases.

Conclusions and Clinical Importance

Midazolam CRI is apparently safe and might be an effective treatment in dogs with CS or SE.

An update on hemilaminectomy of the cranial thoracic spine: Review of six cases

Background:

The optimal surgical approach to relieve spinal cord compression in the cranial thoracic spine is not well described, and the anatomy of the cranial thoracic vertebrae creates added surgical difficulty.

Aim:

This study describes the surgical approach, treatment, and outcome of three dogs and three cats that underwent a cranial thoracic hemilaminectomy for the treatment of extradural spinal cord compression. Surgical positioning was tailored to avoid extensive dissection and provide for a restricted, careful approach.

Methods:

Three dogs and three cats presenting for cranial thoracic spinal cord compression requiring surgical intervention were included.

Results:

All patients were discharged within 5 days. No patients experienced postoperative deterioration in neurologic status, and four animals had improved neurologic status at discharge.

Conclusion:

In cases with cranial thoracic spinal cord compression, the spinous processes can be spared, extensive muscle dissection minimized, and successful outcomes achieved with the appropriate positioning and limited approach.

Eosinophilic meningomyelitis associated with T-cell lymphoma in a cat

A 12-year-old cat was presented for evaluation of progressive tetraparesis. Magnetic resonance imaging of the cervical spine demonstrated T2-hyperintensity, and contrast enhancement within the C4-C7 spinal cord, with marked meningeal contrast enhancement and segmental nerve root thickening. Lumbar cerebrospinal fluid contained 407 total nucleated cells/μL, with 99% eosinophils. The cat transiently improved with prednisolone, clindamycin, and ivermectin therapy, but subsequently worsened and was euthanized. Necropsy revealed an asymmetric infiltration predominantly of the white matter, meninges, and nerve roots of the C4-C6 spinal cord segments by an unencapsulated, poorly demarcated neoplasm composed of atypical lymphocytes admixed with eosinophils, causing perivascular hemorrhage and lytic necrosis. The neoplastic cells were immunoreactive for CD3, ultimately confirming T-cell lymphoma.