What is the likely diagnosis and recommended emergency treatment for a 6‑month‑old infant weighing 6.8 kg who presents afebrile with upward eye rolling and sudden stiffness of the arms and legs?

Likely Diagnosis: Seizure (Neonatal/Infantile Seizure)

This 6-month-old infant presenting with upward eye rolling and sudden stiffness of the arms and legs is most likely experiencing a seizure, and immediate treatment should be initiated with phenobarbital as first-line therapy while simultaneously evaluating for underlying etiology.

Emergency Management Algorithm

Immediate Actions:

1. Stabilize airway, breathing, circulation - Assess for respiratory compromise
2. Administer first-line antiseizure medication:
   • Phenobarbital loading dose: 20 mg/kg IV (for this 6.8 kg infant = approximately 136 mg) 1
   • This is the consensus first-line treatment irrespective of presumed etiology in infants
3. Check bedside glucose - Rule out hypoglycemia as precipitating cause
4. Obtain IV access and send labs: electrolytes, calcium, magnesium, complete blood count, blood culture

Clinical Reasoning:

The presentation of upward eye rolling (oculogyric deviation) with limb stiffness in an afebrile 6-month-old strongly suggests seizure activity. While the infant is technically beyond the neonatal period (0-29 days), the same treatment principles apply for infantile seizures 1.

If Seizures Continue After First-Line Treatment:

Second-line options (if phenobarbital fails to control seizures) 1:

• Phenytoin OR Levetiracetam are both acceptable second-line agents
• Choice depends on suspected etiology once identified
• If cardiac disorders present: prefer levetiracetam
• If channelopathy suspected (based on EEG pattern): prefer sodium channel blocker (phenytoin)

Critical Diagnostic Workup:

• EEG monitoring - Essential to confirm seizure activity and guide treatment 1
• Neuroimaging (MRI brain) - Indicated to identify structural causes 2
• Consider pyridoxine trial (vitamin B6) if seizures are refractory to second-line therapy without identified etiology (50-100 mg IV) 1, 3

Important Differential Considerations

While seizure is most likely, briefly consider:

Benign paroxysmal conditions (less likely given the stiffness):

• Paroxysmal tonic downgaze 3 - typically self-limited, but requires EEG/MRI to exclude seizures
• Benign paroxysmal torticollis 4 - presents with head tilting, not generalized stiffness
• Hyperekplexia 5 - triggered by stimuli, responds to nose-tapping test, treated with clonazepam

Serious conditions requiring urgent consideration:

• Infant botulism 6 - presents with descending paralysis, bulbar symptoms, constipation (not acute stiffening episodes)
• Metabolic derangements - hypocalcemia, hypomagnesemia, hypoglycemia

Key Clinical Pitfalls to Avoid

1. Do NOT delay phenobarbital while waiting for EEG confirmation - clinical diagnosis is sufficient to initiate treatment 1
2. Do NOT assume benign paroxysmal disorder without EEG and neuroimaging - these are diagnoses of exclusion 3
3. Do NOT continue antiseizure medications indefinitely - if acute provoked seizures resolve without evidence of epilepsy, discontinue before discharge regardless of MRI/EEG abnormalities 1
4. Do NOT miss treatable causes - always trial pyridoxine in refractory cases without identified etiology 1

Treatment Duration

If seizures are acute and provoked (e.g., metabolic, infectious cause identified and treated):

• Discontinue antiseizure medication before hospital discharge once seizures have ceased 1
• This applies even if MRI shows abnormalities or EEG background is abnormal
• Early discontinuation prevents unnecessary medication exposure and improves neurodevelopmental outcomes

Weight-Based Dosing for This Patient (6.8 kg):

• Phenobarbital: 136 mg IV loading dose (20 mg/kg)
• Phenytoin (if needed): 136 mg IV loading dose (20 mg/kg)
• Levetiracetam (if needed): 340-476 mg IV (50-70 mg/kg)
• Pyridoxine (if needed): 50-100 mg IV