Fistulous withers causing spinal epidural abscess in a Thoroughbred mare.

Overview

• This case report discusses a 15-year-old Thoroughbred mare diagnosed with fistulous withers that progressed to vertebral osteomyelitis and a spinal epidural abscess (SEA), a severe and previously unreported complication.
• The mare developed acute neurological symptoms due to spinal cord compression and eventually was euthanized, with post-mortem findings confirming the extensive epidural abscess.

Background and Initial Condition

• Fistulous withers: This is a chronic infection of the supraspinous bursa located over the thoracic vertebrae, frequently caused by bacterial infections.
• The mare in this study had chronic fistulous withers, a condition that can cause local inflammation and infection, sometimes leading to more serious complications.
• The common pathogen identified was Escherichia coli, which is frequently isolated in chronic cases of fistulous withers.

Disease Progression and Clinical Signs

• Initially, the mare was treated with standard antibiotics and anti-inflammatory drugs to manage the localized infection.
• Despite this treatment, the mare subsequently developed acute neurologic signs such as hindlimb ataxia (uncoordinated movement) and spastic paresis (muscle stiffness and weakness), indicating possible spinal cord involvement between vertebrae T3 and L3.
• These neurological signs suggested compression of the spinal cord, a serious complication not previously reported in association with fistulous withers.

Diagnostic Findings

• Diagnostic imaging (likely including radiographs, ultrasound, or advanced imaging) revealed vertebral fractures and areas of abscess formation near the spine.
• However, the involvement of the vertebral canal—which houses the spinal cord—was not conclusively identified through imaging at the time.

Treatment and Outcome

• The mare was treated aggressively using:
  • Antimicrobial agents targeting the bacterial infection.
  • Corticosteroids to reduce inflammation.
  • Neuroprotective medications to support spinal cord function.
• Despite these interventions, the mare’s neurological condition worsened, leading to euthanasia.
• Post-mortem examination revealed a large paraspinal abscess that had extended into the epidural space, compressing the spinal cord severely and confirming the presence of a spinal epidural abscess.

Significance and Clinical Implications

• This case is significant because it is the first reported instance of spinal epidural abscess as a complication of fistulous withers in horses.
• It highlights the necessity for veterinarians to consider SEA in the differential diagnosis when horses with chronic paraspinal infections suddenly develop neurological deficits.
• Current limitations in equine diagnostics and treatment options make the prognosis for SEA in horses poor.
• Early diagnosis is critical, ideally through advanced imaging and clinical suspicion, to guide timely surgical intervention and to administer targeted antimicrobial therapy.
• Surgical drainage of abscesses and targeted long-term antibiotic use are likely essential for improving outcomes.

Summary

• The chronic infection known as fistulous withers can rarely progress to severe complications involving vertebral bone infection and spinal epidural abscess formation.
• This progression results in spinal cord compression and significant neurological decline, as demonstrated in this 15-year-old Thoroughbred mare.
• Clinicians should remain vigilant for such complications in cases of chronic paraspinal infection presenting with acute neurological signs, as early recognition and aggressive treatment are crucial for potential recovery.