Differential Diagnosis

The patient's presentation with fever, headache, nonproductive cough, nausea, vomiting, lack of energy, loss of appetite, severe myalgias, nasal congestion, and shortness of breath, along with the laboratory and radiographic findings, suggests a respiratory infection. The differential diagnosis can be categorized as follows:

• Single Most Likely Diagnosis
  • Mycoplasma pneumoniae infection: This is a common cause of community-acquired pneumonia in children and young adults, especially during the winter months. The patient's symptoms, such as fever, headache, nonproductive cough, and myalgias, are consistent with this diagnosis. The elevated CPK and the presence of a right lower lobe infiltrate on the chest x-ray also support this diagnosis.
• Other Likely Diagnoses
  • Influenza: The patient's symptoms, such as fever, headache, myalgias, and cough, are consistent with influenza, especially given the time of year (early January) and the fact that his mother became ill with similar symptoms.
  • Respiratory syncytial virus (RSV) infection: Although more common in younger children, RSV can cause pneumonia in older children, especially those with underlying conditions such as a seizure disorder.
  • Adenovirus infection: Adenovirus can cause a range of respiratory symptoms, including pneumonia, and can be more severe in children with underlying medical conditions.
• Do Not Miss Diagnoses
  • Pneumococcal pneumonia: Although the patient's symptoms and laboratory findings are not typical for pneumococcal pneumonia, it is a potentially life-threatening condition that requires prompt treatment. The presence of a right lower lobe infiltrate and the patient's underlying seizure disorder increase the risk of complications.
  • Influenza A or B with secondary bacterial pneumonia: The patient's symptoms and the fact that his mother became ill with similar symptoms suggest the possibility of influenza, which can be complicated by secondary bacterial pneumonia.
  • Legionnaires' disease: Although less common in children, Legionnaires' disease can cause severe pneumonia and requires prompt treatment.
• Rare Diagnoses
  • Hantavirus pulmonary syndrome: This rare but potentially life-threatening condition can cause severe respiratory symptoms, including pneumonia, and is more common in certain geographic areas.
  • Coronavirus infection (e.g., SARS-CoV-2): Although more commonly associated with adults, coronavirus infections can cause pneumonia in children, especially those with underlying medical conditions.
  • Mycoplasma pneumoniae infection with hemolytic anemia: This rare complication of Mycoplasma pneumoniae infection can cause severe anemia and requires prompt treatment.