What Is Henoch-Schönlein Purpura Nephritis and How Does It Affect the Kidneys?
Henoch-Schönlein purpura nephritis (HSPN) is a secondary glomerular disease that arises as a complication of Henoch-Schönlein purpura (HSP), a type of systemic vasculitis primarily affecting small blood vessels. This condition often develops when the immune system overreacts to various triggers such as infections, food sensitivities, seasonal changes, or exposure to environmental pollutants. While HSP typically manifests with skin purpura—characterized by purple spots on the skin—it can also involve joints, the gastrointestinal tract, and most critically, the kidneys.
Understanding the Causes and Triggers of HSP
Infections, especially upper respiratory tract infections caused by bacteria or viruses, are among the most common initiators of HSP. Additionally, certain foods, medications, insect bites, and climatic shifts have been linked to the onset of this autoimmune response. The condition is more prevalent in children, particularly those between the ages of 2 and 6, although adults can also be affected—albeit less frequently.
Symptoms Beyond the Skin: Systemic Involvement
While skin rash is the hallmark sign, HSP can present with a range of systemic symptoms. Joint pain and swelling, particularly in the knees and ankles, are common and may mimic arthritis. Gastrointestinal involvement can be severe, leading to intense abdominal pain, vomiting, and even gastrointestinal bleeding—manifesting as bloody stools or hematemesis (vomiting blood).
Kidney Involvement: When HSP Progresses to Nephritis
One of the most concerning complications of HSP is renal involvement, known as Henoch-Schönlein purpura nephritis. This typically develops within 4 to 6 weeks after the initial onset of skin symptoms, though in some adults, kidney damage may appear several months later. The primary indicators of kidney injury include hematuria (blood in urine) and proteinuria (excess protein in urine).
In many cases, microscopic or gross hematuria dominates the clinical picture, but proteinuria can vary significantly. In more severe instances, protein loss reaches nephrotic-range levels—exceeding 3.5 grams per day—leading to edema, low serum albumin, and increased risk of thrombosis. If left unmanaged, HSPN can progress to chronic kidney disease or even end-stage renal failure in rare cases.
Diagnosis and Clinical Evaluation
Early and accurate diagnosis is crucial for optimal outcomes. Once HSP is suspected, physicians must conduct a thorough assessment of renal function. Diagnostic tools include urinalysis, blood tests to evaluate kidney function (such as serum creatinine and eGFR), and imaging studies. However, the gold standard for confirming the extent of kidney damage is a renal biopsy.
A kidney biopsy not only confirms the presence of IgA-dominant immune deposits—a hallmark of HSP—but also helps classify the severity of glomerular injury according to standardized histological grading systems. This information guides treatment decisions and provides prognostic insights.
Treatment Strategies and Long-Term Management
Management of HSP nephritis is tailored to the individual's age, symptom severity, and degree of kidney involvement. Mild cases may require only supportive care, including hydration, blood pressure control, and regular monitoring. However, patients with significant proteinuria or impaired kidney function may need immunosuppressive therapy.
Treatments can include corticosteroids, angiotensin-converting enzyme (ACE) inhibitors to reduce proteinuria, and in aggressive cases, agents like cyclophosphamide or mycophenolate mofetil. Pediatric patients generally have a better prognosis, with most recovering fully. Adults, however, face a higher risk of persistent kidney issues and should undergo long-term follow-up.
In conclusion, Henoch-Schönlein purpura nephritis is a potentially serious immune-mediated kidney disorder that demands prompt recognition and careful management. Awareness of its triggers, symptoms, and progression can lead to earlier intervention, preserving kidney function and improving patient outcomes across all age groups.