Correct Answer: A. Henoch-Schonlein purpura
Henoch-Schönlein purpura (HSP, also called IgA vasculitis) is a small-vessel vasculitis mediated by IgA immune complex deposition. The clinical tetrad presented here—palpable blanching purpura (typically on lower extremities and buttocks), arthritis (knees, ankles), abdominal pain (from GI vasculitis), and glomerulonephritis (hematuria + proteinuria)—is pathognomonic for HSP. The purpura is blanching because it is vasculitic inflammation, not thrombocytopenia. HSP is the most common vasculitis in children in India and worldwide. The IgA-dominant immune complex deposition in skin, joints, GI tract, and kidneys (IgA nephropathy pattern) distinguishes it from other vasculitides. Diagnosis is clinical; skin or kidney biopsy showing IgA deposits on immunofluorescence confirms it. The presence of all four components of the tetrad (palpable purpura + arthritis + abdominal pain + renal involvement) makes HSP the only diagnosis that fits. Most cases are self-limited, though renal involvement requires monitoring for progression to chronic kidney disease.
Why the other options are wrong
B. Immune thrombocytopenic purpura — ITP presents with non-blanching petechiae/purpura due to thrombocytopenia (platelet count <150,000/μL), not vasculitis. Critically, ITP does NOT cause arthritis, abdominal pain, or glomerulonephritis. The blanching nature of the rash and the multi-system involvement (joints, GI, kidneys) rule out ITP entirely. NBE may trap students who see 'purpura' and think platelet disorder. C. Dengue — Dengue presents with non-blanching petechial rash, thrombocytopenia, and hemorrhagic manifestations (GI bleeding, epistaxis), but does NOT cause arthritis or glomerulonephritis. While dengue can cause abdominal pain and hematuria (from hemorrhage), it lacks the characteristic palpable purpura on lower extremities and the vasculitic arthritis seen in HSP. Dengue is a viral hemorrhagic fever, not a vasculitis. D. Churg-Strauss syndrome — Churg-Strauss (eosinophilic granulomatosis with polyangiitis, EGPA) is a medium-vessel vasculitis that typically presents in adults with asthma, eosinophilia, and pulmonary involvement—none of which are mentioned here. While it can cause purpura and arthritis, the absence of respiratory symptoms, eosinophilia, and the pediatric presentation make HSP far more likely. EGPA is rare in children in India.
High-Yield Facts
- HSP (IgA vasculitis) tetrad: palpable purpura (lower extremities/buttocks) + arthritis (knees/ankles) + abdominal pain + glomerulonephritis (IgA nephropathy pattern).
- Purpura in HSP is blanching and vasculitic, not thrombocytopenic; platelet count is normal, distinguishing it from ITP.
- IgA immune complex deposition in skin, joints, GI, and kidneys is the pathologic hallmark; confirmed by immunofluorescence microscopy.
- Most common vasculitis in children worldwide and in India; peak age 4–6 years, but can occur up to age 14.
- Renal involvement (IgA nephropathy) occurs in ~50% of HSP cases; hematuria ± proteinuria is the earliest sign; monitor for progression to ESRD.
- Diagnosis is clinical; skin or kidney biopsy with IgA-dominant immunofluorescence confirms; no specific lab test required for diagnosis.
Mnemonics
HSP Tetrad: PAGA Purpura (palpable, lower extremities) + Arthritis (knees/ankles) + GI pain (abdominal) + Arthritis-related renal (glomerulonephritis). Use this when you see a child with purpura + joint pain + belly pain—think HSP first. Blanching vs Non-blanching Purpura Blanching = Vasculitis (HSP, other vasculitides); Non-blanching = Thrombocytopenia or fixed RBC extravasation (ITP, dengue, meningococcemia). Blanching purpura in a child = HSP until proven otherwise.
NBE Trap
NBE pairs 'purpura' with thrombocytopenia (ITP) or hemorrhagic fever (dengue) to trap students who confuse vasculitic purpura with platelet-related purpura. The key discriminator is the blanching nature of the rash and the multi-system vasculitic involvement (arthritis + GI + renal), which are absent in ITP and dengue.
Clinical Pearl
In Indian pediatric practice, HSP is the most common vasculitis presenting to emergency departments. A child with the classic tetrad requires no special investigations for diagnosis—clinical recognition is key. Monitor urine dipstick monthly for 6 months post-onset, as delayed renal involvement (IgA nephropathy) can progress silently to chronic kidney disease if missed.
_Reference: Robbins Ch. 11 (Vasculitis); Harrison Ch. 319 (Vasculitis); OP Ghai Ch. 8 (Pediatric Rheumatology)_