What are the causes of opisthotonic posturing in an infant and how to proceed with investigation and diagnosis?

Opisthotonic Posturing in Infants: Causes and Diagnostic Approach

Immediate Life-Threatening Causes to Exclude First

Opisthotonic posturing in an infant is a medical emergency requiring immediate assessment for life-threatening conditions, particularly severe central nervous system infections, metabolic derangements, and drug toxicity. 1

Critical Initial Assessment

• Airway, Breathing, Circulation (ABC): Assess conscious level using AVPU scale (Alert, responds to Voice, responds to Pain, Unresponsive) or children's Glasgow coma scale; evaluate pupillary size and reaction to light; observe for convulsive movements 1
• Immediate bedside glucose: Hypoglycemia (blood sugar < 3 mmol/L) may precipitate coma and opisthotonic posturing and must be excluded immediately 1
• Vital signs: Document heart rate, respiratory rate, blood pressure, and temperature to identify shock, respiratory distress, or fever 1

Primary Differential Diagnoses

1. Central Nervous System Infections

Cerebral malaria presents with impaired consciousness, convulsions, abnormal neurological signs, and opisthotonic posturing as cardinal features 1. However, consider other CNS infections:

• Meningitis/Encephalitis: Examine for neck stiffness or full fontanel; these findings suggest alternative CNS infections rather than malaria 1
• Herpes simplex virus encephalitis: Can present with opisthotonic posturing, particularly during reactivation or relapse 2
• Scrub typhus with GBS: Opisthotonic posturing has been reported in Guillain-Barré syndrome associated with scrub typhus infection 3

2. Drug Withdrawal or Toxicity

• Neonatal drug withdrawal: Opisthotonic posturing occurs with glutethimide withdrawal, presenting with increased tone, tremors, high-pitched cry, hyperactivity, and irritability 1
• 4-Aminopyridine toxicity: Ingestion causes dramatic opisthotonic posturing with vermiform tongue fasciculations and neuromuscular irritability 4
• Benzodiazepine withdrawal: Can present with hypertonia, hyperreflexia, and tremors 1

3. Movement Disorders

• Status dystonicus: Life-threatening movement disorder with gradually worsening dystonic spasms, opisthotonic posturing, tachycardia, tachypnea, and desaturation; occurs in children with preexisting dystonia or following acute CNS insult 5

4. Gastroesophageal Reflux Disease (GERD)

• Sandifer syndrome: Secondary to gastroesophageal reflux, presenting as paroxysms of abnormal head posturing (including opisthotonic posturing) after eating in young children 1
• Dystonic neck posturing in infants: A clinical feature of pathological gastroesophageal reflux 1

5. Immunodeficiency

• X-linked severe combined immunodeficiency (X-SCID): Rare association with opisthotonic posturing in the setting of severe infections, though the mechanism remains unclear 6

Diagnostic Workup Algorithm

Immediate Investigations (Within Minutes)

1. Point-of-care glucose: Rule out hypoglycemia immediately 1
2. Vital signs monitoring: Continuous assessment for shock, respiratory compromise 1
3. Neurological examination: Assess consciousness level, pupillary responses, posture, and presence of seizures 1

Urgent Laboratory Studies (Within 1 Hour)

• Complete blood count with differential: Assess for infection, immunodeficiency 1
• Blood culture: If fever or signs of sepsis present 1
• Electrolytes, calcium, magnesium: Rule out metabolic derangements 1
• Arterial or venous blood gas: Assess for acidosis 1
• Toxicology screen: If drug exposure suspected (maternal drug use, accidental ingestion) 1, 4

Lumbar Puncture (If No Contraindications)

• Cerebrospinal fluid analysis: Cell count, glucose, protein, Gram stain, bacterial culture 1
• CSF PCR: For herpes simplex virus, enterovirus if encephalitis suspected 2
• Consider: Scrub typhus serology (IgM) in endemic areas if GBS suspected 3

Neuroimaging

• Brain CT or MRI: Indicated if focal neurological signs, altered consciousness, or concern for intracranial hemorrhage, malformation, or structural lesion 1, 2, 5
• Look for: Hemorrhage, malformation, atrophy, acute infarction, or signs of raised intracranial pressure 1

Specialized Testing Based on Clinical Context

• Electroencephalogram (EEG): If seizures suspected; note that opisthotonic posturing can occur without seizure activity on EEG 4
• Nerve conduction studies: If Guillain-Barré syndrome suspected (progressive weakness, areflexia, facial weakness) 3
• Upper GI series or pH probe: If Sandifer syndrome suspected (posturing after feeds, vomiting, irritability) 1
• Immunologic evaluation: If recurrent severe infections suggest immunodeficiency 6

Critical Management Principles

Immediate Stabilization

• Airway management: Children with Glasgow coma score ≤ 8 or features of raised intracranial pressure warrant elective intubation and ventilation 1
• Correct hypoglycemia immediately: If blood glucose < 3 mmol/L 1
• Seizure management: If seizures present, treat with lorazepam 0.1 mg/kg IV/IO 1
• Benzodiazepines for drug toxicity: Repeated doses of benzodiazepines (lorazepam 0.05 mg/kg) for opisthotonic posturing due to drug toxicity 4

Common Pitfalls to Avoid

• Do not assume opisthotonic posturing equals seizures: EEG may be negative despite dramatic posturing 4
• Do not delay lumbar puncture if CNS infection suspected, unless contraindications present (signs of raised ICP, coagulopathy, hemodynamic instability) 1
• Do not overlook drug withdrawal: Obtain detailed maternal drug history in neonates; withdrawal symptoms may appear days to weeks after birth 1
• Do not miss Sandifer syndrome: Consider GERD in infants with posturing after feeds, even without obvious reflux symptoms 1
• Do not attribute all posturing to raised intracranial pressure: Only a small proportion of children with opisthotonic posturing have raised ICP 1