Differential Diagnosis

The patient's presentation of fever, tachycardia, and hypotension with normal laboratory and imaging results requires a thorough consideration of potential causes. The differential diagnosis can be categorized as follows:

• Single Most Likely Diagnosis
  • Septic Shock with an Atypical Source: Despite normal WBC and urinalysis, the clinical presentation suggests sepsis. The source of infection might not be immediately apparent, requiring further investigation into less common sites of infection or non-infectious causes of sepsis-like syndrome.
• Other Likely Diagnoses
  • Adrenal Insufficiency: This condition can present with hypotension, fever, and tachycardia, especially in the context of a stressor like infection or trauma. Normal laboratory results do not rule out adrenal insufficiency, as cortisol levels can be normal in early stages.
  • Toxic Shock Syndrome: Although often associated with infections, toxic shock syndrome can present with fever, hypotension, and tachycardia without an obvious source of infection or abnormal laboratory findings initially.
  • Cardiogenic Shock: Myocardial infarction or other cardiac conditions can lead to hypotension and tachycardia. A normal chest X-ray does not exclude cardiac issues, and further cardiac-specific testing is warranted.
• Do Not Miss Diagnoses
  • Pulmonary Embolism: Despite a normal chest X-ray, pulmonary embolism can present with tachycardia, hypotension, and fever. It is crucial to consider this diagnosis due to its high mortality if untreated.
  • Aortic Dissection: This is a life-threatening condition that can cause hypotension and tachycardia. A normal CT of the abdomen and pelvis does not entirely rule out an aortic dissection, especially if the dissection involves the ascending aorta.
  • Neurogenic Shock: Resulting from spinal cord injury, this condition can lead to hypotension without the typical signs of shock like tachycardia, though bradycardia is more common. However, in the early stages, tachycardia can be present.
• Rare Diagnoses
  • Thyroid Storm: A life-threatening complication of untreated or undertreated hyperthyroidism, presenting with fever, tachycardia, and potentially hypotension.
  • Pheochromocytoma: A rare tumor of the adrenal gland that can cause episodic or sustained hypertension but also hypotension in certain cases, along with tachycardia and fever.
  • Hemorrhagic Shock with a Non-visible Source: Internal bleeding not evident on initial CT scans, such as from a small bowel or mesenteric source, could lead to hypotension and tachycardia.

Each of these diagnoses requires careful consideration and further investigation to determine the underlying cause of the patient's symptoms.