Diagnosis: IgA Vasculitis (Henoch-Schönlein Purpura)
The clinical presentation of fever, rash, arthritis, ankle edema, and microscopic hematuria over 1 week is most consistent with IgA vasculitis (Henoch-Schönlein purpura). 1
Clinical Reasoning
The diagnosis of IgA vasculitis is strongly supported by the presence of the classic tetrad:
- Palpable purpura/rash - The skin eruption is a cardinal feature 1, 2
- Arthritis/arthralgia - Joint involvement is characteristic 1, 2
- Renal involvement - Microscopic hematuria indicates glomerular involvement 1, 2, 3
- Edema - Ankle edema fits the typical presentation 1
Why Not SLE?
SLE can be distinguished from IgA vasculitis by several key features 1:
- IgA vasculitis presents with palpable purpura, whereas SLE typically has different cutaneous manifestations 1
- SLE characteristically has positive ANA and diverse systemic manifestations that are not described in this case 1, 4
- The acute 1-week presentation with the classic tetrad strongly favors IgA vasculitis over SLE's more varied and chronic presentation 1
Why Not Granulomatosis with Polyangiitis (GPA)?
GPA has distinct features that are absent in this case 1:
- Upper respiratory tract involvement (sinusitis, nasal crusting) is characteristic of GPA but not mentioned here 1
- Lower respiratory tract disease (hemoptysis, diffuse alveolar hemorrhage) occurs in GPA but is absent 1
- Approximately 90% of GPA patients have positive PR3-ANCA or MPO-ANCA, which is not typical of IgA vasculitis 1
- The absence of respiratory symptoms and presence of the classic tetrad strongly favor IgA vasculitis over GPA 1
Diagnostic Confirmation
A skin biopsy should be performed for histological and immunofluorescence studies to confirm IgA deposits in vessel walls, which is the sine qua non for diagnosis 3. The finding of IgA deposits in vessel walls associated with small-vessel vasculitis is pathognomonic 3.
Important Clinical Considerations
Renal Monitoring
The European Renal Association recommends monitoring renal function and blood pressure, as hypertension and renal insufficiency can develop with worsening nephritis 1. IgA vasculitis nephritis can lead to chronic renal failure in up to 20% of pediatric patients after 20 years of follow-up 3.
Common Pitfall
Do not wait for the complete tetrad to be present - the clinical picture of IgA vasculitis is often incomplete, and any component of the triad may be absent 2, 5. The diagnosis should be considered even with partial manifestations when the key features of palpable purpura and systemic involvement are present 2.