IgA Vasculitis (Henoch-Schönlein Purpura)
The most likely diagnosis is IgA vasculitis (Henoch-Schönlein purpura), a small vessel vasculitis characterized by the classic tetrad of palpable purpura, arthralgia, abdominal pain, and renal involvement, typically triggered by an antecedent upper respiratory infection.
Clinical Reasoning
This 70-year-old man presents with the pathognomonic features of IgA vasculitis:
- Palpable purpuric lesions on lower extremities, buttocks, and posterior arms (classic distribution)
- Arthralgia with periarticular swelling but no warmth or erythema (non-erosive inflammatory arthritis pattern)
- Abdominal pain (gastrointestinal involvement)
- Preceding upper respiratory infection 3 weeks prior (common trigger)
- Normal coagulation studies excluding thrombocytopenic purpura
- Normal CBC excluding hematologic malignancy
The non-painful, non-pruritic nature of the rash and its palpable quality strongly distinguish this from other dermatologic conditions. The temporal relationship with URI is highly characteristic, as HSP typically develops 1-3 weeks post-infection 1, 2, 3.
Age-Related Considerations
While HSP predominantly affects children (>90% of cases), adult-onset disease—particularly in elderly patients—is well-documented but carries important prognostic implications 4, 2:
- More severe clinical course in adults
- Higher risk of chronic kidney disease and renal complications
- Greater likelihood of requiring immunosuppressive therapy
- 20-fold lower incidence but worse outcomes compared to pediatric cases
The presentation in a 70-year-old is atypical by age but classic by clinical features 2, 5.
Diagnostic Confirmation
Skin biopsy remains the gold standard and should be performed promptly 1. Expected findings include:
- Leukocytoclastic vasculitis on histology
- IgA immune complex deposition in dermal vessel walls (pathognomonic)
- Neutrophilic and eosinophilic infiltration
Given the abdominal pain, urinalysis is critical to assess for renal involvement (hematuria, proteinuria), even though initial urinalysis was reported as negative. Serial monitoring is essential as renal disease may develop later 3, 5.
Critical Pitfalls to Avoid
- Do not dismiss this as simple purpura or attribute it to age-related vascular fragility—the palpable quality and distribution are diagnostic
- Do not delay skin biopsy waiting for symptom progression; early histologic confirmation guides management
- Monitor renal function closely—acute kidney injury can develop rapidly in elderly patients 6, 3
- Exclude other vasculitides: Check ANCA (to rule out microscopic polyangiitis), ANA, RF, and inflammatory markers (ESR/CRP) 7
Management Approach
For this patient with moderate disease (arthralgia, abdominal pain, purpura without organ-threatening complications):
Initial therapy:
- Supportive care with NSAIDs for mild-moderate joint symptoms
- Corticosteroids if NSAIDs insufficient: Prednisone 0.5-1 mg/kg/day (typically 40-60 mg daily in adults) 2, 3, 5
- Monitor for gastrointestinal bleeding (can present as hematemesis or rectal bleeding) 1, 3
Steroid tapering: Once improvement achieved, taper to lowest effective dose over 4-6 weeks. Target maintenance ≤10 mg/day prednisone equivalent if prolonged therapy needed 3, 5.
Escalation criteria: If inadequate response to steroids or steroid-sparing needed, consider:
- Mycophenolate mofetil 1000 mg twice daily 1
- Cyclophosphamide for severe organ involvement (pulmonary hemorrhage, rapidly progressive glomerulonephritis) 5
Monitoring Requirements
- Serial urinalysis weekly initially, then monthly for 6 months (renal involvement can be delayed)
- Serum creatinine monitoring
- Blood pressure checks (hypertension suggests renal disease)
- Stool guaiac if abdominal symptoms persist
The excellent response to corticosteroids reported in multiple case series supports their use as first-line therapy in adults with HSP 2, 3, 5.