What is the diagnostic approach for a patient, likely a child or young adult, presenting with symptoms such as palpable purpura, abdominal pain, arthralgias, and renal involvement, to confirm IgA vasculitis?

Diagnostic Approach for IgA Vasculitis

IgA vasculitis is primarily a clinical diagnosis based on the characteristic tetrad of palpable purpura (non-thrombocytopenic), arthralgias, abdominal pain, and renal involvement, with skin biopsy showing leukocytoclastic vasculitis and IgA deposition confirming the diagnosis when the clinical picture is unclear. 1

Clinical Diagnosis

The diagnosis of IgA vasculitis relies predominantly on recognizing the classic clinical presentation rather than laboratory testing:

• Palpable purpura is the hallmark feature, appearing as non-thrombocytopenic purpuric lesions typically distributed on the lower extremities and buttocks 1, 2
• Arthralgias or arthritis affecting large joints, particularly knees and ankles 1
• Abdominal pain is present in the majority of cases (92.59% in one series), often presenting as acute abdominal pain that may precede the rash 3
• Renal involvement manifests as microscopic hematuria with dysmorphic red blood cells, red cell casts, and proteinuria 4, 1

A critical pitfall: In adults, gastrointestinal symptoms may precede purpura, making early diagnosis challenging and potentially delaying recognition of the disease. 3

Essential Laboratory Evaluation

While IgA vasculitis is clinically diagnosed, specific testing is needed to exclude other diagnoses and assess organ involvement:

• Urinalysis with microscopy is mandatory to detect hematuria, red cell casts, and proteinuria indicating renal involvement 4, 5
• Complete blood count to confirm normal platelet count (excluding thrombocytopenic purpura) and assess for leukocytosis 3, 6
• Renal function tests (serum creatinine, GFR estimation) to evaluate kidney involvement severity 5, 1
• Inflammatory markers (CRP, ESR) are typically elevated, along with elevated D-dimer and fibrinogen, with decreased albumin 3
• ANCA testing (MPO-ANCA and PR3-ANCA by antigen-specific immunoassay) should be performed to exclude ANCA-associated vasculitis, which requires different management 4, 7

Diagnostic testing is required only to exclude other etiologies of purpura and to identify the extent of renal involvement—not to confirm IgA vasculitis itself. 1

Skin Biopsy Confirmation

• Skin biopsy of purpuric lesions reveals leukocytoclastic vasculitis with IgA deposition on immunofluorescence, providing definitive histopathologic confirmation 1, 2
• Biopsy is particularly useful when the clinical presentation is atypical or when purpura appears before other manifestations 1
• The finding of IgA-dominant immune complex deposition distinguishes IgA vasculitis from other forms of small-vessel vasculitis 1

Assessment of Organ Involvement

Renal Assessment

• 24-hour urine collection for protein quantification when proteinuria is detected on urinalysis 5
• Kidney biopsy should be considered when there is significant proteinuria (>1 g/day), declining renal function, or nephritic syndrome to determine the extent of glomerulonephritis and guide treatment decisions 1, 8
• Renal biopsy provides critical prognostic information, as the extent of renal involvement determines long-term outcomes 1, 8

Gastrointestinal Assessment

• Abdominal imaging (CT or ultrasound) when abdominal symptoms are prominent, looking for bowel wall thickening (present in 58% of cases), which most commonly affects the duodenum and ileum 3
• Endoscopy may reveal congestion, erosions, and ulcers, particularly in the duodenum and ileum 3
• Imaging or endoscopy is indicated to assess for complications such as intussusception or gastrointestinal bleeding 1, 3

Additional Assessments

• Scrotal examination and ultrasound in all male patients, as scrotal involvement (orchitis) occurs more frequently than recognized and affects treatment decisions 2
• Blood pressure monitoring as part of renal assessment 1

Differential Diagnosis Considerations

Several conditions can mimic IgA vasculitis and must be excluded:

• Other small-vessel vasculitides (ANCA-associated vasculitis, cryoglobulinemic vasculitis) are distinguished by ANCA positivity or hepatitis C serology 4, 7
• Systemic lupus erythematosus and other connective tissue diseases may present with purpura and are identified by ANA and other autoantibodies 4
• Infections and malignancies can closely mimic vasculitis and require appropriate evaluation 4
• Thrombocytopenic purpura is excluded by normal platelet count 1

Key Clinical Distinctions

Adult IgA vasculitis differs significantly from pediatric disease, with a higher risk of progression to end-stage renal disease and more severe complications. 8 Adults are more likely to have:

• Elevated white blood cell count and neutrophil-to-lymphocyte ratio, particularly when gastrointestinal symptoms precede purpura 3
• More severe and persistent renal involvement requiring closer monitoring 8
• Higher rates of complications including gastrointestinal bleeding and orchitis 1, 2

Follow-Up Monitoring

• Six months of follow-up is recommended at minimum to assess for disease relapse or remission, as IgA vasculitis can relapse years after initial presentation 1
• Serial urinalysis and renal function monitoring are essential, as renal involvement can persist and relapse even after apparent resolution 1, 8