Differential Diagnosis for a 3-Month-Old with a Runny Nose

Single Most Likely Diagnosis

• Common Cold (Viral Rhinitis): This is the most common cause of a runny nose in infants, often due to viral infections such as rhinovirus, coronavirus, or adenovirus. The justification for this diagnosis is the high prevalence of viral upper respiratory infections in this age group and the typical presentation of a runny nose.

Other Likely Diagnoses

• Allergic Rhinitis: Although less common in infants, allergic reactions to environmental allergens like dust mites, pet dander, or pollen can cause rhinitis symptoms. Justification: Increasing awareness of early onset allergies and the possibility of exposure to allergens from birth.
• Infectious Rhinitis (Bacterial): Bacterial infections can also cause a runny nose, though they are less common than viral causes. Justification: The possibility of secondary bacterial infection following a viral upper respiratory infection.
• Irritant Rhinitis: Exposure to irritants like smoke, strong odors, or changes in humidity can cause rhinitis symptoms. Justification: Infants are often exposed to various environmental factors that could irritate their nasal passages.

Do Not Miss Diagnoses

• Congenital Nasal Anomalies: Conditions such as choanal atresia or nasal septal deviation can cause persistent nasal discharge. Justification: These conditions are critical to identify early as they may require surgical intervention.
• Cystic Fibrosis: Although rare, cystic fibrosis can present with chronic nasal congestion and discharge among other symptoms. Justification: The importance of early diagnosis for management and prognosis.
• Immunodeficiency: Severe or recurrent infections, including those causing a runny nose, can be a sign of an underlying immunodeficiency. Justification: Early detection of immunodeficiency is crucial for the management and prevention of severe infections.

Rare Diagnoses

• Nasal Foreign Body: Infants may insert small objects into their noses, leading to unilateral nasal discharge. Justification: Although rare, this condition requires prompt recognition and removal of the foreign body to prevent complications.
• Tumor or Mass: Rarely, a runny nose in an infant can be a sign of a nasal or sinus tumor. Justification: The importance of considering all possible causes, even if rare, to ensure appropriate diagnosis and treatment.