Tetralogy of Fallot with undiagnosed asthma: a diagnostic challenge in the management of recurrent hypercyanotic spells – a case report

Abstract

Hypercyanotic ("Tet") spells in children with Tetralogy of Fallot (TOF) are life-threatening events often triggered by identifiable precipitants such as infections or dehydration. The presence of a comorbidity that mimics or exacerbates these spells presents a significant diagnostic and therapeutic challenge. Case Summary: We report the case of a 7-year-old boy with a known history of TOF, previously stable on prophylactic propranolol. He presented with a four-month history of recurrent, severe hypercyanotic spells requiring multiple hospital admissions, initially attributed to acute respiratory infections. During his most recent admission, clinical examination revealed widespread rhonchi and a hyperinflated chest radiograph, raising suspicion of underlying bronchial asthma. A marked therapeutic response to nebulised salbutamol and systemic corticosteroids confirmed the diagnosis. Propranolol was discontinued. The patient showed rapid and sustained improvement and has remained free of hypercyanotic episodes for two months on as-needed bronchodilator therapy alone. Conclusion: This case underscores the critical importance of actively investigating for new, treatable precipitants, such as asthma, in any child with TOF who presents with a changing pattern or increasing frequency of hypercyanotic spells. It also highlights the risk for long-term propranolol use in unmasking or exacerbating latent bronchial hyperactivity, creating a management dilemma where standard cardiac prophylaxis may worsen respiratory comorbidity.