Differential Diagnosis for Mucus with Slight Tinge of Blood in a 5-Month-Old

Single Most Likely Diagnosis

• Allergic Rhinitis or Nasal Irritation: This is a common condition in infants that can cause mucus production with a slight tinge of blood due to nasal irritation. The persistence of symptoms despite the elimination of common allergens like cow milk, egg, and soya suggests that the cause might not be related to these foods.

Other Likely Diagnoses

• Gastroesophageal Reflux Disease (GERD): Although GERD typically presents with symptoms like spitting up and irritability, it can sometimes cause nasal congestion and irritation leading to bloody mucus.
• Upper Respiratory Infection: Viral infections can cause nasal discharge that may be bloody due to the fragility of the nasal mucosa in infants.
• Environmental Allergens: Exposure to environmental allergens like dust, pollen, or pet dander could cause allergic rhinitis symptoms.

Do Not Miss Diagnoses

• Foreign Body in the Nose: This is a critical diagnosis to consider because it can cause persistent, unilateral nasal discharge that may be bloody. It's a common accident in toddlers but can also occur in infants who are old enough to put objects in their noses.
• Nasal Polyps or Tumors: Although rare in infants, these conditions can cause persistent nasal discharge and bleeding.

Rare Diagnoses

• Cystic Fibrosis: This genetic disorder can cause persistent respiratory symptoms, including nasal congestion and discharge, but it's typically associated with other systemic symptoms like failure to thrive and recurrent infections.
• Primary Ciliary Dyskinesia: A rare genetic disorder affecting the cilia in the respiratory tract, leading to chronic respiratory infections and nasal congestion.
• Hemangiomas or Vascular Malformations in the Nose: These are rare congenital conditions that can cause nasal bleeding and discharge.

Each of these diagnoses should be considered in the context of the infant's overall health, growth, and additional symptoms. A thorough physical examination and possibly further diagnostic tests may be necessary to determine the underlying cause of the symptoms.