Presentation of HSP Purpuric Lesions
The hallmark presentation of Henoch-Schönlein Purpura (HSP) is palpable purpura on the lower extremities and buttocks, typically appearing as non-blanching, raised purpuric macules that patients can feel under their fingertips. 1, 2
Characteristic Skin Findings
The purpuric lesions in HSP have distinct features that differentiate them from other causes of purpura:
- Palpable quality: The purpura is raised and can be felt on palpation, distinguishing it from non-palpable purpura seen in thrombocytopenia or coagulopathies 3, 2
- Distribution pattern: Lesions predominantly affect the lower extremities (legs, ankles) and buttocks, with gravity-dependent distribution 1, 2
- Appearance: Non-blanching, purpuric macules that may start as erythematous papules before evolving into characteristic purpura 4
- Symmetry: Typically bilateral and symmetric in distribution 5
Temporal Presentation Pattern
The skin manifestations follow a predictable pattern:
- Lesions typically appear after a prodromal period, though they may be the first presenting sign 2, 6
- The rash can precede or follow other systemic manifestations (arthritis, abdominal pain, renal involvement) 5, 7
- Critical pitfall: In some cases, abdominal symptoms precede cutaneous lesions by days to weeks, making early diagnosis challenging 5, 7
Associated Clinical Features
HSP presents as a clinical tetrad, though not all features need be present simultaneously:
- Arthritis/arthralgia: Typically affects knees and ankles, often accompanying the rash 2, 5
- Abdominal pain: Can range from mild discomfort to severe, paroxysmal pain with gastrointestinal bleeding 5, 7
- Renal involvement: Manifests as hematuria, proteinuria, or acute kidney injury 2, 4
Diagnostic Confirmation
Skin biopsy remains the gold standard for confirming HSP diagnosis, showing leukocytoclastic vasculitis with IgA-dominant immune complex deposition in dermal vessel walls. 1, 5
The formal diagnostic approach recommended by the American Society of Nephrology includes:
- Documentation of palpable purpura on physical examination 1
- Histopathological confirmation showing IgA deposition when feasible 1, 5
- Assessment for organ involvement (renal, gastrointestinal, joint) 1
- Exclusion of other vasculitides through negative ANCA and anti-GBM antibodies 1
Key Diagnostic Pitfalls to Avoid
- Never dismiss palpable purpura as simple dermatitis without evaluating for systemic vasculitis 3
- Do not assume all lower extremity purpura in adults is HSP—consider ANCA-associated vasculitis, drug reactions, and infectious causes 3
- Recognize that gastrointestinal symptoms may precede skin findings by days to weeks, delaying diagnosis 5, 7
- Palpate all purpuric lesions to distinguish palpable from non-palpable purpura, as this fundamentally changes the differential diagnosis 3
Management Approach
While the question focuses on presentation, initial management considerations include:
- Supportive care for mild cases, as HSP is typically self-limited 6
- Corticosteroids (methylprednisolone) for severe manifestations, particularly gastrointestinal or renal involvement 5
- Addition of immunosuppressants (mycophenolate mofetil) for steroid-refractory cases 5
- Close monitoring for renal complications, which determine long-term prognosis 1, 4