Most Likely Diagnosis: Henoch-Schönlein Purpura (IgA Vasculitis)
The answer is E. Henoch-Schönlein purpura (HSP). This patient presents with the classic tetrad of HSP: palpable purpuric rash predominantly on the lower extremities, abdominal pain with gastrointestinal bleeding (bloody stools), hematuria indicating renal involvement, and a temporal relationship to an upper respiratory tract infection 1, 2, 3.
Clinical Reasoning
Why HSP is the Correct Diagnosis
The constellation of findings is pathognomonic for HSP:
- Palpable purpuric maculopapular rash on lower limbs: This is the hallmark feature of HSP, representing IgA-mediated small vessel vasculitis 3, 4
- Post-infectious timing: HSP characteristically develops days after upper respiratory tract infections, commonly caused by adenovirus or enterovirus 3
- Multi-system involvement: The simultaneous presentation of dermatologic, gastrointestinal, and renal manifestations is classic for HSP 1, 2
- Gastrointestinal bleeding: Occurs in 50-85% of HSP patients, with bloody stools being a common manifestation 5
Why Other Options Are Incorrect
A. Peptic ulcer flare-up: Would not explain the purpuric rash on lower extremities or hematuria. Peptic ulcer disease presents with epigastric pain and potential upper GI bleeding but lacks the systemic vasculitic features.
B. Crohn's disease: While Crohn's can cause abdominal pain and bloody stools, it does not present acutely after URI with purpuric rash on lower extremities or hematuria. Crohn's typically has a more insidious onset with chronic symptoms.
C. Post-streptococcal glomerulonephritis: Presents with hematuria and follows streptococcal infection, but does not cause purpuric rash or gastrointestinal bleeding. The latency period is also typically longer (1-3 weeks post-infection).
D. IgA nephropathy: Can cause hematuria following URI, but isolated IgA nephropathy does not present with purpuric rash or gastrointestinal bleeding. HSP is actually considered the systemic form of IgA-mediated disease, while IgA nephropathy is the isolated renal form.
Important Clinical Pitfalls
Diagnostic Challenges
Abdominal symptoms may precede rash: In 14-40% of HSP cases, gastrointestinal symptoms appear before the characteristic purpura, which can lead to misdiagnosis and unnecessary procedures including appendectomy 1, 6. The rash may appear up to 10-14 days after initial abdominal symptoms 1.
Key distinguishing feature: The palpable purpura on lower extremities is the critical diagnostic clue that differentiates HSP from purely gastrointestinal or renal pathology. The distribution pattern (predominantly lower limbs) and palpable quality are highly specific 2, 3.
Confirmation Strategy
If diagnosis remains uncertain before rash appears:
- Skin biopsy showing IgA deposition in superficial dermal vessel walls is the gold standard 2
- Biopsy of normal-appearing skin or duodenum can reveal IgA deposits even before visible purpura develops 6
- Elevated serum IgA levels support the diagnosis 4
Clinical Significance
HSP is the most common systemic vasculitis in childhood 3, 7. The temporal relationship to upper respiratory infection, combined with the specific pattern of multi-system involvement (skin, GI tract, kidneys), makes this diagnosis highly probable. The patient requires monitoring for renal complications, which can be severe and represent the most significant long-term morbidity in HSP 3.