Differential Diagnosis for Acute Low Back Pain with Renal Implications

The patient's presentation of acute low back pain, nausea, vomiting, and a history of moving furniture, combined with pitting edema, diffuse macular rash, elevated serum potassium, elevated creatinine, and markedly elevated urea, suggests a complex clinical picture that involves both musculoskeletal and renal systems. The presence of fever adds an infectious or inflammatory component to the differential diagnosis.

• Single Most Likely Diagnosis
  • Acute Tubular Necrosis (ATN): Given the acute onset of renal failure indicators (elevated creatinine, urea, and potassium) in the context of a potential nephrotoxic or ischemic insult (possibly from dehydration due to nausea and vomiting, or from the physical exertion of moving furniture), ATN is a strong consideration. The fever could be related to the underlying cause of ATN or a secondary infection.
• Other Likely Diagnoses
  • Acute Interstitial Nephritis (AIN): The presence of a diffuse macular rash and fever, alongside renal dysfunction, could suggest AIN, especially if the patient has been exposed to new medications or substances that could cause an allergic interstitial nephritis. However, the absence of specific drug history or other typical causes of AIN makes it slightly less likely than ATN.
  • Pyelonephritis: The combination of fever, flank pain (which could be described as low back pain), and signs of renal dysfunction could suggest an upper urinary tract infection like pyelonephritis. The presence of nausea and vomiting could be consistent with a systemic infection.
• Do Not Miss Diagnoses
  • Sepsis: Although less directly related to the renal findings, the presence of fever, nausea, vomiting, and potential renal dysfunction could be part of a septic picture, especially if the patient has a source of infection that is not immediately apparent. Sepsis can lead to ATN and has a high mortality if not promptly recognized and treated.
  • Rhabdomyolysis: This condition, characterized by muscle breakdown, can lead to ATN and presents with muscle pain, elevated creatinine, and very high levels of serum potassium. The history of moving furniture could be a risk factor for muscle injury.
• Rare Diagnoses
  • Vasculitis: Conditions like ANCA-associated vasculitis or lupus nephritis could present with renal dysfunction, rash, and systemic symptoms. However, these are less common and would typically require additional specific findings or laboratory results to support the diagnosis.
  • Endocarditis: Although rare, infective endocarditis can present with systemic symptoms including fever, rash, and renal dysfunction due to embolic phenomena or immune complex deposition. It would be a consideration in patients with known heart disease or intravenous drug use.