What Causes BRUE
By definition, BRUE has no identifiable cause after thorough history and physical examination—it is a diagnosis of exclusion that can only be made when no explanation is found. 1
Understanding BRUE as "Unexplained"
The fundamental characteristic of BRUE is that it remains unexplained after appropriate clinical evaluation. 1 This distinguishes it from events that may appear similar but have identifiable causes:
- If a cause is identified, it is NOT a BRUE 1, 2
- The presence of fever, nasal congestion, or increased respiratory effort suggests viral infection and precludes BRUE diagnosis 1, 2
- Events with choking after vomiting suggest gastroesophageal reflux and should not be classified as BRUE 1
Potential Underlying Etiologies (When Found, It's Not BRUE)
While BRUE itself is unexplained, the American Academy of Pediatrics acknowledges that a broad range of disorders can present with similar symptoms before being ruled out through evaluation: 1
Serious Conditions to Exclude:
- Child abuse (must assess for inconsistent history, unexplained bruising, or changing accounts) 1
- Congenital abnormalities 1
- Epilepsy and seizure disorders 1, 3
- Inborn errors of metabolism 1
- Infections 1, 3
- Cardiac conditions 3
- Airway abnormalities 3
Common Benign Conditions That Mimic BRUE:
- Periodic breathing of the newborn (normal physiology, not BRUE) 1
- Breath-holding spells 1
- Dysphagia 1
- Gastroesophageal reflux (GER found in 33% of high-risk cases when investigated) 1, 4
- Overfeeding (recent evidence shows mean daily weight gain of 41g vs 35g in controls, suggesting overfeeding as a risk factor) 5
Critical Clinical Pitfall
The most important pitfall is misunderstanding that BRUE is NOT a cause—it is a descriptive term for an unexplained event. 1, 2 The American Academy of Pediatrics emphasizes that clinicians must distinguish between:
- Events that are truly unexplained (BRUE) 1
- Events that appear concerning but have identifiable causes (not BRUE) 1, 2
- Normal infant physiology misinterpreted as pathologic (facial flushing, periodic breathing—not BRUE) 2
When Events Occur
While not causative, contextual factors are important for risk stratification:
- 53.7% of high-risk BRUE episodes occur during or immediately after feeding 4
- Mixed breastfeeding patterns show higher association with BRUE (33% vs 17% in controls, though not statistically significant) 5
- Low birth weight is statistically associated with GERD-related events 4
The Diagnostic Approach
A thorough history and physical examination are required to exclude identifiable causes before diagnosing BRUE. 1 Key historical features to assess include: 1
- Witness reliability and consistency of history
- Infant's state before event (awake/asleep, feeding, position)
- Event characteristics (duration, color change, breathing pattern, muscle tone, responsiveness)
- Intervention required to resolve event
- Presence of fever, respiratory symptoms, or vomiting
For most well-appearing infants after the event, the risk of serious underlying disorder or recurrence is extremely low. 1, 2 However, serious diagnoses are found in less than 5% of cases, most commonly seizures and airway abnormalities. 3