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 treatment makes this less likely, and lupus nephritis would typically be accompanied by other systemic symptoms and autoantibody evidence.

• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)

  • B) Lupus nephritis: Although considered less likely, missing lupus nephritis could have significant consequences due to its potential for severe renal and systemic complications if not promptly treated.
  • D) Post streptococcal glomerulonephritis: While the clinical context makes this less likely, it's crucial not to miss this diagnosis due to its potential for causing rapid deterioration of renal function.

• Rare diagnoses

  • C) Pyelonephritis: This condition, an infection of the kidney, is less likely given the presentation and the lack of symptoms suggestive of a urinary tract infection (e.g., dysuria, flank pain). The presence of eosinophilia and WBC casts without significant bacteriuria or symptoms of infection makes pyelonephritis an unlikely diagnosis.
  • Other rare conditions such as vasculitides (e.g., ANCA-associated vasculitis) or drug-induced vasculitis could be considered but are less likely without additional specific symptoms or findings.