Differential Diagnosis for Unexplained Fever in a Baby

When approaching a case of unexplained fever in a baby, it's crucial to consider a wide range of potential causes due to the non-specific nature of fever and the vulnerability of this age group. The differential diagnosis can be organized into the following categories:

• Single Most Likely Diagnosis
  • Viral infection: This is often the most common cause of fever in infants. Viruses such as respiratory syncytial virus (RSV), influenza, and adenovirus can cause fever without specific localizing signs.
• Other Likely Diagnoses
  • Bacterial infection (e.g., urinary tract infection, pneumonia, bacteremia): These infections can present with fever and non-specific symptoms in infants.
  • Teething: Though controversial, some infants may develop a low-grade fever during teething.
  • Vaccination reaction: Fever can occur as a reaction to certain vaccinations, particularly live vaccines.
• Do Not Miss Diagnoses
  • Meningitis: A potentially life-threatening infection of the meninges that requires prompt diagnosis and treatment.
  • Sepsis: Bacterial sepsis can present with non-specific symptoms including fever and can rapidly progress to a life-threatening condition.
  • Congenital infections (e.g., congenital syphilis, toxoplasmosis, rubella): These infections can cause fever among other symptoms and have significant long-term implications if not treated.
  • Kawasaki disease: An acute febrile illness of childhood that can lead to coronary artery aneurysms if not recognized and treated.
• Rare Diagnoses
  • Autoimmune disorders (e.g., juvenile idiopathic arthritis): Though rare in infancy, these conditions can cause recurrent or persistent fever.
  • Lymphoma or leukemia: Malignancies that can present with fever of unknown origin.
  • Inborn errors of metabolism: Certain metabolic disorders can cause episodic or persistent fever.
  • Chronic granulomatous disease: A rare genetic disorder affecting the immune system, leading to recurrent infections and fever.

Each of these diagnoses requires careful consideration based on the clinical presentation, age of the infant, and exposure history. A thorough physical examination, laboratory tests, and sometimes imaging studies are necessary to narrow down the differential diagnosis and guide appropriate management.