Differential Diagnosis

• Single most likely diagnosis
  • Neurogenic cough or habit cough: The child's cough started at 2 months, was initially associated with fever, but continued without fever, and is described as heavy and spasmodic without diurnal variation. The lack of response to antibiotics and the presence of cough without other significant symptoms suggest a non-infectious etiology. The child's development is appropriate, and there's no cyanosis at rest, but cyanosis with crying could indicate that the cough is causing respiratory distress.
• Other Likely diagnoses
  • Chronic lung disease of infancy (CLDI): Given the child's history of cough and fast breathing since 2 months, and the need for oxygen, CLDI is a consideration, especially in the context of diffuse ground glass opacities on HRCT.
  • Interstitial lung disease (ILD): The HRCT findings of diffuse ground glass opacities with subpleural sparing are suggestive of ILD. The child's symptoms and the lack of response to antibiotics also support this diagnosis.
  • Recurrent infections or chronic infection: Although the child has been treated with antibiotics and the cultures are negative, the possibility of a chronic or recurrent infection cannot be entirely ruled out, especially with the dirty mucosa seen on bronchoscopy.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Cystic fibrosis: Although the sweat chloride level is normal, cystic fibrosis can present with respiratory symptoms, and a normal sweat test does not entirely rule out the disease, especially in infants.
  • Immunodeficiency: The child's recurrent infections or chronic infection could be a sign of an underlying immunodeficiency, which would be critical to diagnose and manage appropriately.
  • Congenital heart disease with pulmonary hypertension: Although the 2D ECHO is structurally normal, pulmonary hypertension could explain the child's need for oxygen and desaturation. This condition would require prompt diagnosis and treatment.
• Rare diagnoses
  • Surfactant protein deficiencies: These are rare genetic disorders that can cause respiratory distress and chronic lung disease in infants. The HRCT findings could be consistent with this diagnosis.
  • Lymphangiomatosis: A rare condition that could cause chronic respiratory symptoms and diffuse lung involvement.
  • Pulmonary alveolar proteinosis: A rare condition characterized by the accumulation of surfactant-like protein and phospholipids in the alveoli, which could present with chronic respiratory symptoms and diffuse ground glass opacities on imaging.