Equine Neonatal Maladjustment Syndrome Study Guide

Overview and Clinical Importance

Neonatal Maladjustment Syndrome (NMS), also known as hypoxic ischemic encephalopathy (HIE), perinatal asphyxia syndrome (PAS), or colloquially as "dummy foal syndrome," is one of the most common noninfectious neurological disorders affecting neonatal foals. This syndrome affects approximately 1-5% of all equine births and represents a significant topic on the NAVLE examination.

Affected foals exhibit behavioral abnormalities and neurologic deficits that are not attributable to infectious, toxic, congenital, or metabolic causes. The historical terminology of "barkers," "wanderers," "convulsants," and "dummy foals" reflects the clinical presentation spectrum observed in these patients.

Pathophysiology

Traditional Hypoxic-Ischemic Theory

The traditional understanding centers on hypoxia and ischemia occurring during the perinatal period. Decreased oxygen delivery to the fetal brain results in a cascade of cellular injury.

Cellular Injury Cascade

• Energy failure: Shift from oxidative to anaerobic metabolism depletes cellular ATP
• Membrane depolarization: Disruption of ion homeostasis leads to cellular swelling
• Excitotoxicity: Release of glutamate causes excessive neuronal stimulation
• Oxidative stress: Free radicals and lipid peroxidation damage cell membranes
• Calcium accumulation: Intracellular calcium overload activates destructive enzymes

Neurosteroid Persistence Theory (UC Davis Research)

Recent research from UC Davis has identified an alternative mechanism involving persistence of neuroinhibitory steroids (progestogens, pregnenolone, allopregnanolone, DHEA) that normally keep the fetus sedated during gestation.

Key findings: Progesterone levels in NMS foals were found to be up to 80-fold higher than normal, with other neurosteroids elevated 3,000 to 12,000 times higher than in healthy foals. These neurosteroids cross the blood-brain barrier and modulate GABA receptors, producing sedation.

Etiology and Risk Factors

Red Bag Delivery (Premature Placental Separation)

Red bag delivery occurs when the chorioallantois (outer placental membrane) fails to rupture at the cervical star and instead separates from the uterine wall prematurely. This condition accounts for 5-10% of all cases of abortion, stillbirth, and perinatal death.

Recognition: The red, velvety chorioallantois appears at the vulva instead of the normal grayish-white amnion. This is a FOALING EMERGENCY requiring immediate intervention - the placenta must be cut open immediately to allow the foal access to oxygen.

Clinical Signs

Clinical presentation is highly variable and forms the basis for historical descriptive names. Foals may appear normal at birth but typically develop signs within hours to 24-48 hours postpartum. Some foals are abnormal immediately at birth.

Spectrum of Clinical Signs

Multi-Organ Involvement

While CNS signs are most prominent, perinatal asphyxia syndrome (PAS) can affect multiple organ systems:

• Renal: Anuria, oliguria, elevated creatinine
• Gastrointestinal: Colic, ileus, meconium impaction, gastric ulcers, necrotizing enterocolitis
• Cardiovascular: Arrhythmias, poor cardiac output, systemic hypotension
• Pulmonary: Impaired surfactant production, ventilation-perfusion mismatch, atelectasis
• Hepatic: Elevated GGT, hyperbilirubinemia

Diagnosis

NMS is primarily a clinical diagnosis of exclusion based on behavioral observations. There is no definitive antemortem diagnostic test. The clinician must rule out other causes of neurologic signs in neonates including sepsis, meningitis, trauma, hypoglycemia, and congenital abnormalities.

Normal Neonatal Milestones

Normal Neonatal Vital Signs

Laboratory Findings

Laboratory abnormalities are neither specific nor diagnostic but help assess severity and multi-organ involvement:

• Creatinine: Transient elevation at birth suggests placental insufficiency; should decrease greater than 50% within 24 hours with supportive care
• Creatine Kinase (CK): Elevated levels correlate with hypoxic-ischemic muscle injury
• GGT: Elevation indicates hepatic injury
• Blood Gas: May show hypoxemia, hypercarbia, acidemia
• IgG: ALWAYS assess passive transfer - greater than 800 mg/dL adequate; less than 400 mg/dL = complete failure of passive transfer (FTPI)
• Lactate: Elevated with tissue hypoperfusion

Treatment

Treatment is primarily supportive and addresses multiple body systems. Early intervention significantly improves outcomes.

The Madigan Squeeze Technique

Developed by Dr. John Madigan at UC Davis, this non-pharmacological technique mimics birth canal pressure to signal termination of sedative neurosteroid production.

Technique Protocol

• Use soft rope (5/8 to 3/4 inch diameter, 16-18 feet length)
• Create bowline knot with fixed loop (honda-style)
• Loop rope around foal's thorax at withers level
• Apply 10-20 lbs of constant pressure
• Maintain pressure for 20 minutes (mimics birth canal transit time)
• Release pressure and allow foal to wake naturally

Contraindications

• Rib fractures
• Respiratory distress
• Congenital anomalies
• Foals that have never stood
• Confirmed hypoxic brain injury

Seizure Management

Supportive Care

Nutritional Support

• Ensure colostrum intake within 6-12 hours (critical window for IgG absorption)
• 50 kg foal requires minimum 1.5-2 L colostrum
• If unable to nurse: nasogastric tube feeding q1-2h at 20-30% body weight per 24 hours
• Total parenteral nutrition if GI dysfunction present

Fluid Therapy

• Maintenance: 3 mL/kg/hr IV polyionic fluids
• Avoid glucose-containing fluids initially (hyperglycemia worsens hypoxic injury)
• Supplement potassium as needed

Additional Treatments

• Oxygen supplementation: Intranasal insufflation 5-10 L/min
• Plasma transfusion: If IgG less than 800 mg/dL; typically 1-2 L IV
• Antibiotics: Broad-spectrum coverage to prevent secondary infections
• DMSO: May reduce cerebral edema
• Mannitol: 0.25-1 g/kg IV for cerebral edema
• GI protectants: Omeprazole for gastric ulcer prevention

Nursing Care

• Maintain sternal recumbency; turn frequently to prevent pressure sores
• Padded environment to prevent injury during seizures
• Warm, quiet, dark environment to minimize stimulation
• Eye protection/lubrication (corneal ulcers common during seizures)
• Maintain normothermia

Prognosis

The prognosis for NMS foals is generally favorable with appropriate supportive care:

• Overall survival rate: 70-80% of uncomplicated cases
• Recovery timeline: Mildly affected foals may recover in 2 days; severely affected foals may take 7+ days
• Long-term outcome: Most foals that survive develop into normal adults with no residual neurologic deficits
• Athletic performance: Once racing age, performance similar to age-matched cohort

Negative Prognostic Indicators

• Concurrent sepsis
• Persistent coma/unresponsive state
• No improvement within first 5 days
• Severe, recurrent seizures refractory to treatment
• Multi-organ dysfunction
• Abnormal placentation/mare illness during pregnancy

Differential Diagnosis

NMS is a diagnosis of exclusion. Rule out: