Differential Diagnosis for Pneumonia Etiology

Given the symptoms of sudden left lower quadrant (LRQ) ache, bilateral flank pain, temperature, general malaise, elevated blood pressure (BP), and heart rate (HR), the differential diagnosis can be categorized as follows:

• Single Most Likely Diagnosis

  • Pneumococcal Pneumonia: This is a common cause of community-acquired pneumonia, which can present with sudden onset of symptoms including pain, fever, and systemic signs such as elevated BP and HR. The flank pain could be referred pain from the lower lobes of the lungs.

• Other Likely Diagnoses

  • Viral Pneumonia: Various viruses can cause pneumonia, which might present similarly to bacterial pneumonia, including symptoms like fever, malaise, and pain. The presence of bilateral flank pain could be indicative of a more systemic infection.
  • Influenza: Especially during flu season, influenza can cause pneumonia and present with sudden onset of high fever, body aches, and respiratory symptoms. The systemic symptoms like elevated BP and HR could be part of the body's response to the infection.
  • Pyelonephritis: Although primarily a urinary tract infection, pyelonephritis can cause flank pain and systemic symptoms like fever and elevated BP. However, the presence of LRQ ache and the context of pneumonia etiology make it less likely but still a consideration.

• Do Not Miss Diagnoses

  • Pulmonary Embolism (PE): While less common, PE can present with sudden onset of symptoms including chest pain, which might be referred to the flanks, and systemic signs like tachycardia and elevated BP. It's crucial to consider PE due to its high mortality rate if untreated.
  • Sepsis: Any infection, including pneumonia, can lead to sepsis, a life-threatening condition. The presence of fever, elevated BP and HR, and general malaise could indicate the onset of sepsis, making prompt diagnosis and treatment critical.
  • Endocarditis: In rare cases, especially in patients with pre-existing heart conditions, pneumonia can be complicated by or be a result of endocarditis, an infection of the heart valves. This condition requires immediate medical attention.

• Rare Diagnoses

  • Q Fever: Caused by Coxiella burnetii, Q fever is a rare cause of pneumonia that can present with atypical symptoms, including flank pain due to possible renal involvement.
  • Mycoplasma Pneumonia: While more common in younger populations, Mycoplasma pneumonia can cause a wide range of symptoms, including extrapulmonary manifestations like arthralgias, which might be mistaken for flank pain.
  • Histoplasmosis: A fungal infection that can cause pneumonia, especially in immunocompromised individuals or those exposed to bird or bat droppings. It can present with systemic symptoms and might cause flank pain if there's involvement of the spleen or kidneys.