Differential Diagnosis

The patient's presentation with facial swelling, eosinophilia, and WBC casts in the urine after antibiotic treatment for a sore throat suggests an allergic or immune-mediated reaction. Here's a categorized differential diagnosis:

• Single most likely diagnosis

  • A) Acute interstitial nephritis: This condition is often caused by an allergic reaction to medications, including antibiotics. The presence of eosinophilia and WBC casts in the urine supports this diagnosis, as they are indicative of an inflammatory response in the kidneys.

• Other Likely diagnoses

  • D) Post streptococcal glomerulonephritis: Although less likely given the context of antibiotic treatment and the specific urinary findings, this condition could still be considered, especially if the sore throat was due to a streptococcal infection. However, the presence of eosinophilia and WBC casts is more suggestive of interstitial nephritis.
  • B) Lupus nephritis: This is an autoimmune condition that could present with renal involvement, including casts in the urine. However, the acute onset following antibiotic use and the specific finding of eosinophilia make it less likely compared to acute interstitial nephritis.

• Do Not Miss

  • Severe allergic reactions or anaphylaxis: Although not directly a renal diagnosis, the facial swelling and eosinophilia could be part of a severe allergic reaction. It's crucial to assess the patient's airway, breathing, and circulation and to consider anaphylaxis as a potential cause, especially if there are other symptoms such as difficulty breathing or a drop in blood pressure.
  • Vasculitis: Conditions like granulomatosis with polyangiitis (formerly known as Wegener's granulomatosis) could present with renal involvement and eosinophilia. While less common, these conditions are critical to diagnose due to their potential for severe morbidity.

• Rare diagnoses

  • Eosinophilic granulomatosis with polyangiitis (Churg-Strauss syndrome): A rare autoimmune condition characterized by asthma, eosinophilia, and vasculitis. It could potentially present with renal involvement, but it is much less common than acute interstitial nephritis.
  • IgA nephropathy or Henoch-Schönlein purpura: These conditions could present with renal symptoms following an infection, but the specific findings of eosinophilia and WBC casts, along with the temporal relationship to antibiotic use, make them less likely in this scenario.