What is the diagnosis for a 3-year-old child presenting with a cough, low energy (lethargy) for approximately 5 days, worsening at night, with vital signs showing normothermia (temperature 98.0), hypotension (blood pressure 85/57), and mild hypoxemia (oxygen saturation 93% on room air)?

Differential Diagnosis for a 3-year-old with Cough, Low Energy, and Nighttime Symptoms

Single most likely diagnosis

• Viral upper respiratory infection (URI): The symptoms of cough, low energy, and worsening at night are common in viral URIs, which are prevalent in children. The vital signs are relatively stable, supporting a benign cause.

Other Likely diagnoses

• Acute bronchiolitis: This is a common lower respiratory tract infection in young children, often caused by respiratory syncytial virus (RSV). The cough and low energy could be consistent with bronchiolitis, especially if the child has a history of exposure or is in a high-risk group.
• Pneumonia: Although the oxygen saturation is 93% on room air, which is relatively preserved, pneumonia should be considered, especially if the child has a fever, cough, and worsening symptoms at night.
• Asthma: If the child has a history of wheezing or asthma, an exacerbation could present with cough, low energy, and nighttime symptoms.

Do Not Miss (ddxs that may not be likely, but would be deadly if missed)

• Pneumocystis jirovecii pneumonia (PCP): Although rare in immunocompetent children, PCP can occur in those with HIV/AIDS or other immunocompromised states. It's crucial to consider this diagnosis to avoid missing a potentially life-threatening condition.
• Foreign body aspiration: This is an emergency that can present with sudden onset of cough, choking, or respiratory distress. Although the history does not suggest a clear aspiration event, it's essential to consider this possibility, especially if the child's symptoms worsen or if there are signs of respiratory distress.
• Congenital heart disease with pulmonary hypertension: Children with undiagnosed congenital heart disease may present with nonspecific symptoms like cough and low energy. It's crucial to consider this diagnosis to avoid missing a potentially life-threatening condition.

Rare diagnoses

• Tuberculosis (TB): Although rare in young children, TB can present with chronic cough, low energy, and nighttime symptoms. A thorough history, including exposure to TB, and diagnostic testing would be necessary to consider this diagnosis.
• Cystic fibrosis: This genetic disorder can present with recurrent respiratory infections, cough, and low energy. Although rare, it's essential to consider this diagnosis in children with persistent or recurrent symptoms.