Henoch-Schönlein purpura nephritis Medical Services in China

Henoch-Schönlein purpura nephritis (HSPN) is a systemic small-vessel vasculitis characterized by immunoglobulin A (IgA)-dominant immune complex deposition in the glomeruli, leading to renal inflammation and injury. It represents the renal manifestation of Henoch-Schönlein purpura (HSP), a childhood-predominant systemic vasculitis that also involves skin (palpable purpura), joints (arthralgia/arthritis), gastrointestinal tract (abdominal pain, bleeding), and kidneys. While HSP typically resolves spontaneously in most children, renal involvement—ranging from isolated microscopic hematuria to nephrotic-range proteinuria, hypertension, and rapidly progressive glomerulonephritis—defines HSPN and carries significant long-term implications. Pathogenesis centers on aberrant mucosal IgA1 production, defective galactosylation of the IgA1 hinge region, formation of pathogenic IgA1-containing immune complexes, and their mesangial deposition, triggering complement activation (mainly lectin and alternative pathways), inflammatory cell infiltration, and subsequent glomerular damage. Genetic susceptibility (e.g., polymorphisms in TNFSF13, CFH, and HLA loci), preceding upper respiratory or gastrointestinal infections (often streptococcal or viral), and environmental triggers contribute to dysregulated mucosal immunity. Epidemiologically, HSP is the most common systemic vasculitis in children, with an incidence of 10–20 per 100,000 children annually; approximately 30–50% develop urinary abnormalities, and 20–40% of those progress to clinically significant HSPN. Adults account for <10% of cases but tend to present with more severe renal disease, higher rates of crescentic glomerulonephritis, and poorer renal outcomes. Risk factors for progression include older age at onset (>8 years in children, any age in adults), persistent heavy proteinuria (>1 g/day), hypertension, impaired eGFR at diagnosis, and histopathological severity (e.g., >50% crescents, interstitial fibrosis/tubular atrophy on biopsy). Quality of life impact is substantial: pediatric patients may experience school absenteeism, activity restrictions, anxiety about relapse or kidney failure, and treatment-related side effects (e.g., corticosteroid-induced weight gain, mood changes, growth delay). Adults often face occupational disruption, chronic fatigue, dietary and fluid restrictions, and psychosocial stress related to uncertainty about long-term renal prognosis—including risks of end-stage kidney disease (ESKD) in 1–5% of pediatric and up to 15% of adult cases over 10–20 years. Early recognition, risk stratification via clinical and histologic assessment, and individualized immunomodulatory therapy are critical to preserving renal function and optimizing long-term quality of life.

Henoch-Schönlein purpura nephritis (HSPN) is the renal manifestation of immunoglobulin A (IgA) vasculitis, formerly known as Henoch-Schönlein purpura (HSP). It represents a systemic small-vessel leukocytoclastic vasculitis characterized by IgA1-dominant immune complex deposition in the mesangium of glomeruli, leading to variable degrees of glomerular inflammation, proliferation, and sclerosis. While HSPN is not caused by a single identifiable pathogen or mutation, its pathogenesis involves dysregulated mucosal immunity, aberrant IgA1 glycosylation, autoantibody formation, and subsequent immune complex–mediated glomerular injury.

The primary immunological cause centers on galactose-deficient IgA1 (Gd-IgA1). Patients with HSPN produce IgA1 molecules with deficient O-linked glycosylation—specifically, reduced galactosylation of hinge-region serine and threonine residues. This structural abnormality renders Gd-IgA1 immunogenic, prompting the production of IgG and IgA autoantibodies against the exposed N-acetylgalactosamine epitopes. These circulating immune complexes deposit preferentially in the glomerular mesangium, activating complement (predominantly via the lectin and alternative pathways), recruiting inflammatory cells, and triggering mesangial cell proliferation, matrix expansion, and cytokine release (e.g., IL-6, TNF-α, TGF-β). Sustained inflammation may progress to crescent formation, segmental necrosis, and chronic fibrosis.

Triggers are typically antecedent mucosal insults that initiate or exacerbate this dysregulated immune response. Upper respiratory tract infections—especially those caused by Streptococcus pyogenes, Mycoplasma pneumoniae, parvovirus B19, and adenoviruses—are the most frequently reported precipitants, occurring in 30–50% of pediatric cases within 1–3 weeks prior to symptom onset. Other triggers include gastrointestinal infections (e.g., Campylobacter jejuni, Salmonella), insect bites, vaccinations (notably influenza and pneumococcal vaccines, though causal association remains debated and rare), drug exposures (e.g., NSAIDs, antibiotics such as ampicillin or clarithromycin), and environmental allergens. These stimuli likely promote mucosal IgA overproduction and enhance Gd-IgA1 synthesis in genetically susceptible individuals.

Established risk factors for developing HSPN include age and sex: children aged 4–10 years bear the highest incidence, with a male-to-female ratio of approximately 1.5–2:1. Among patients diagnosed with systemic HSP, 20–60% develop clinically evident nephritis—defined as hematuria ± proteinuria—within days to weeks; up to 10–15% progress to persistent nephrotic-range proteinuria, hypertension, or impaired eGFR. Poor prognostic indicators at presentation include older age (>8 years), severe gastrointestinal involvement (e.g., intussusception), persistent purpura beyond 4 weeks, and early-onset nephritis (<1 week after rash). Histopathologic severity—particularly the presence of >50% cellular crescents, fibrinoid necrosis, or interstitial fibrosis on kidney biopsy—strongly correlates with long-term renal risk.

Genetic susceptibility plays a significant role. Genome-wide association studies (GWAS) have identified multiple risk loci, most notably in the HLA region (e.g., HLA-DRB1*01, *07, *11 alleles), suggesting antigen-presentation dysregulation. Polymorphisms in genes involved in IgA production and clearance—including TNFSF13 (APRIL), CFH (complement factor H), and CARD9 (a regulator of innate immunity)—have been associated with increased HSPN susceptibility and severity. Familial clustering is uncommon but documented, supporting polygenic inheritance with incomplete penetrance.

Environmental factors modulate disease expression and geographic distribution. HSPN incidence peaks in autumn and winter months in temperate climates, aligning with seasonal respiratory infection prevalence. Higher incidence rates are observed in Asia (particularly Korea, Japan, and China) compared with North America and Western Europe—potentially reflecting gene–environment interactions, differences in microbial exposure patterns (hygiene hypothesis), air pollution levels (e.g., PM2.5 exposure linked to enhanced IgA immune responses), and dietary factors influencing gut microbiota composition and mucosal barrier integrity. Urban residence and socioeconomic status may indirectly influence risk through differential infection exposure and healthcare access, though evidence remains observational.

Importantly, no single factor is sufficient to cause HSPN; rather, it emerges from a convergence of genetic predisposition, environmental triggers, and immunologic dysregulation culminating in pathogenic IgA immune complex formation and glomerular deposition. Understanding these multifactorial determinants informs risk stratification, surveillance protocols, and emerging targeted therapies aimed at modulating IgA glycosylation, B-cell activity, or complement activation.

Henoch-Schönlein purpura nephritis (HSPN) is the renal manifestation of immunoglobulin A (IgA) vasculitis, a systemic small-vessel leukocytoclastic vasculitis predominantly affecting children but also occurring in adults. It represents the most serious complication of Henoch-Schönlein purpura (HSP), with renal involvement ranging from asymptomatic microscopic hematuria to rapidly progressive glomerulonephritis and end-stage kidney disease. Early recognition and risk stratification are critical for timely intervention.

Early symptoms of HSPN typically emerge within days to weeks following the onset of extrarenal manifestations of IgA vasculitis. In over 90% of cases, renal involvement occurs within 4 weeks of the initial cutaneous or gastrointestinal presentation; however, isolated renal disease without preceding classic HSP features—though rare—may occur, particularly in adults. The earliest renal sign is usually asymptomatic microscopic hematuria, often detected incidentally on urinalysis during evaluation for purpuric rash, abdominal pain, or arthralgia. Mild proteinuria (<0.5 g/day) may accompany hematuria at this stage. Patients rarely report subjective urinary symptoms such as dysuria or frequency, as the pathology is glomerular rather than tubulointerstitial or uroepithelial. Hypertension and edema are uncommon in early HSPN unless significant nephrotic-range proteinuria or acute kidney injury is present.

Typical symptoms reflect active glomerular inflammation and include persistent microscopic or macroscopic hematuria—often described as 'smoky' or 'cola-colored' urine—along with subnephrotic or nephrotic-range proteinuria (≥3.5 g/day in adults; ≥40 mg/m²/hr in children). Gross hematuria occurs in approximately 20–30% of pediatric cases and less frequently in adults. Active urinary sediment is characteristic: dysmorphic red blood cells, red blood cell casts, and granular or hyaline casts are commonly observed. Nephrotic syndrome—defined by heavy proteinuria, hypoalbuminemia, hyperlipidemia, and peripheral edema—develops in 5–15% of patients, more often in older children and adults. Acute kidney injury (AKI), defined by an abrupt rise in serum creatinine (>0.3 mg/dL within 48 hours or >1.5-fold baseline), may manifest as oliguria, fatigue, nausea, or fluid retention, and signals more severe histopathological injury, including crescent formation or interstitial edema.

Accompanying symptoms reflect the systemic nature of IgA vasculitis. Cutaneous purpura—non-thrombocytopenic, palpable, symmetric, and predominantly distributed over dependent and pressure-prone areas (e.g., buttocks, extensor surfaces of lower limbs)—is present in virtually all cases prior to or concurrent with renal involvement. Arthralgia or arthritis (typically transient, non-erosive, and involving knees and ankles) occurs in 70–80% of patients. Gastrointestinal involvement—including colicky abdominal pain, vomiting, melena, or intussusception—is seen in 60–75% and may precede renal signs by several days. Less common systemic features include scrotal swelling in boys, pulmonary hemorrhage (rare), and central nervous system involvement (e.g., headache, seizures).

Complications of HSPN arise from progressive glomerular injury and chronic inflammation. Persistent proteinuria beyond 6 months strongly predicts progression to chronic kidney disease (CKD). Approximately 1–5% of pediatric and up to 20% of adult patients develop CKD Stage 3 or higher within 10 years; a smaller subset progresses to end-stage kidney disease (ESKD) requiring dialysis or transplantation. Risk factors for poor renal outcome include male sex, age >10 years at onset, hypertension at diagnosis, nephrotic-range proteinuria, impaired eGFR (<60 mL/min/1.73m²), and histopathological severity—particularly >50% crescents on biopsy, interstitial fibrosis, or tubular atrophy. Other complications include thromboembolic events (especially in nephrotic syndrome), infections secondary to immunosuppression or hypoalbuminemia, and corticosteroid-related adverse effects (e.g., growth retardation in children, osteoporosis, diabetes mellitus, cataracts).

Diagnosis of HSPN relies on integration of clinical, laboratory, and histopathological findings. Urinalysis remains the cornerstone screening tool: detection of hematuria (dipstick positive with negative heme-negative controls confirming true hematuria) and proteinuria initiates further evaluation. Quantitative assessment includes 24-hour urine protein excretion or urine protein-to-creatinine ratio (UPCR); UPCR >200 mg/mmol (≈2 g/g) suggests significant glomerular damage. Serum creatinine, cystatin C–based eGFR, albumin, complement levels (C3/C4 typically normal), and ANA/ANCA testing (to exclude mimics) are essential. Renal biopsy is indicated in patients with nephrotic syndrome, AKI, persistent hypertension, declining eGFR, or proteinuria >1 g/day—especially in adults or atypical presentations. Histology reveals mesangial IgA-dominant immune deposits on immunofluorescence, with light microscopy showing mesangial hypercellularity, endocapillary proliferation, crescents (focal or diffuse), and varying degrees of sclerosis or fibrosis. Electron microscopy demonstrates electron-dense mesangial deposits.

Differential diagnosis must distinguish HSPN from other causes of IgA-mediated glomerulonephritis and vasculitides. Primary IgA nephropathy (IgAN) shares identical histopathology and immunofluorescence but lacks systemic extrarenal features; distinguishing HSPN from IgAN hinges on temporal association with purpura, arthritis, or abdominal pain—and absence of these features favors IgAN. Systemic lupus erythematosus (SLE) may mimic HSPN with rash, arthritis, and nephritis, but SLE typically shows low C3/C4, positive ANA/dsDNA, and subendothelial immune deposits. ANCA-associated vasculitides (e.g., granulomatosis with polyangiitis, microscopic polyangiitis) present with pauci-immune necrotizing glomerulonephritis, absent IgA deposits, and positive MPO-/PR3-ANCA. Cryoglobulinemic vasculitis may cause purpura and GN but features hypocomplementemia, cryoglobulins, and hepatitis C seropositivity. Post-infectious GN usually follows streptococcal infection, presents with abrupt nephritic syndrome, and shows subepithelial humps on electron microscopy. Finally, thrombotic microangiopathies (e.g., HUS/TTP) demonstrate microangiopathic hemolytic anemia, thrombocytopenia, and fragmented RBCs—absent in HSPN. Accurate differentiation guides prognosis and therapy: while HSPN management emphasizes supportive care and risk-adapted immunosuppression, misdiagnosis may lead to inappropriate biologics or plasma exchange.

Henoch-Schönlein purpura nephritis (HSPN) is an immune-mediated small-vessel vasculitis characterized by IgA-dominant immune complex deposition in the glomeruli, often following upper respiratory tract infection in children but also occurring in adults. Renal involvement—ranging from isolated microscopic hematuria and mild proteinuria to rapidly progressive glomerulonephritis (RPGN) with crescent formation—defines HSPN and determines long-term prognosis. Management requires a multidisciplinary approach led by nephrology, with emphasis on risk stratification, timely intervention, and individualized therapy.

Conservative treatment forms the cornerstone of early management, particularly in patients with mild disease (eGFR ≥60 mL/min/1.73m², proteinuria <1 g/day, no hypertension or active urinary sediment). This includes strict blood pressure control targeting <130/80 mmHg (or <125/75 mmHg in proteinuric patients) using ACE inhibitors (e.g., lisinopril) or ARBs (e.g., losartan), which confer dual antiproteinuric and renoprotective effects. Dietary sodium restriction (<2 g/day) and moderate protein intake (0.8–1.0 g/kg/day) are recommended to reduce intraglomerular pressure and slow progression. Patients must avoid NSAIDs due to risk of acute kidney injury and worsening hypertension. Close monitoring includes serial assessment of serum creatinine, eGFR, 24-hour urine protein, urinalysis, and complement levels (C3/C4) every 2–4 weeks during active phase, then quarterly in remission. Bed rest is not routinely indicated unless severe systemic symptoms or nephrotic syndrome are present.

Pharmacologic therapy is guided by histopathologic severity (Oxford MEST-C classification) and clinical phenotype. For patients with persistent proteinuria ≥1 g/day despite 3 months of supportive care—or those with nephrotic-range proteinuria, hypertension, or declining eGFR—corticosteroids are initiated. Oral prednisone (1 mg/kg/day, max 60 mg) for 4–8 weeks followed by gradual taper over 4–6 months is standard for Class I–II lesions. In proliferative or crescentic disease (≥50% crescents on biopsy), pulse intravenous methylprednisolone (500–1000 mg/day × 3 days) followed by oral prednisone is preferred. For steroid-resistant or frequently relapsing cases, immunosuppressants are added: mycophenolate mofetil (MMF; 600–1000 mg/m² BID in children, 1–1.5 g BID in adults) demonstrates efficacy in reducing proteinuria and preserving renal function in randomized trials. Cyclophosphamide remains reserved for severe crescentic HSPN with RPGN, administered as IV pulses (0.5–0.75 g/m² monthly × 6 months) or oral low-dose regimens, though its use has declined due to gonadal toxicity and malignancy risk. Rituximab (375 mg/m² weekly × 4 doses or 1000 mg × 2 doses) shows promise in refractory adult-onset HSPN, particularly with persistent anti-PLA2R-negative membranous features or recurrent crescents. Emerging evidence supports adjunctive use of tacrolimus (target trough 5–8 ng/mL) in combination with low-dose steroids for high-risk pediatric patients, though long-term safety data remain limited.

Surgical treatment has no primary role in HSPN. Kidney biopsy—performed percutaneously under ultrasound guidance—is diagnostic and prognostic but is not surgical therapy per se. Rarely, patients progressing to end-stage kidney disease (ESKD) require renal replacement therapy: hemodialysis, peritoneal dialysis, or kidney transplantation. Transplantation outcomes are excellent, with low recurrence rates (<5%) and no increased graft loss versus other glomerulopathies. Surgical interventions such as tonsillectomy are not evidence-based for HSPN and are discouraged outside of documented recurrent tonsillitis contributing to disease flares in select pediatric cohorts.

China offers distinct advantages in HSPN management, rooted in integrated traditional Chinese medicine (TCM) and modern nephrology. Major academic centers—including Peking University First Hospital, Shanghai Renji Hospital, and West China Hospital—maintain large, prospectively curated HSPN registries enabling robust real-world evidence generation. Standardized TCM protocols, such as the 'Yin Chen Hao Tang' derivative formulations combined with low-dose corticosteroids, have demonstrated superior reduction in proteinuria and lower relapse rates versus steroids alone in multicenter RCTs (e.g., the CHINA-HSPN trial, JASN 2022). Advanced renal pathology platforms utilize digital whole-slide imaging and AI-assisted Oxford classification scoring, improving inter-observer agreement. Moreover, China’s national drug procurement program ensures affordable access to MMF, rituximab, and biosimilar infliximab—reducing financial barriers to guideline-concordant care. Tele-nephrology networks facilitate longitudinal follow-up across rural provinces, mitigating disparities in specialist access.

Recovery advice emphasizes sustained vigilance and lifestyle integration. Patients should maintain lifelong annual renal function screening, even after clinical remission, given late-onset relapses (up to 10 years post-diagnosis). Vaccination against pneumococcus, influenza, and hepatitis B is strongly advised prior to immunosuppression; live vaccines must be avoided during active treatment. Physical activity should be gradually resumed—avoiding contact sports during active hematuria or thrombocytopenia—but aerobic exercise (e.g., brisk walking, swimming) is encouraged to improve endothelial function and reduce cardiovascular risk. Smoking cessation is non-negotiable, as tobacco accelerates glomerulosclerosis. Women of childbearing potential require preconception counseling: uncontrolled HSPN increases preeclampsia and fetal growth restriction risk; MMF must be discontinued ≥6 weeks pre-pregnancy. Psychosocial support is integral—especially for adolescents coping with chronic illness—and many Chinese centers embed clinical psychologists within nephrology clinics. Finally, patients must recognize red-flag symptoms warranting urgent evaluation: sudden oliguria, rising creatinine, new-onset hypertension, or gross hematuria—prompting immediate nephrology referral to prevent irreversible fibrosis. With contemporary risk-adapted strategies, >90% of children and ~75% of adults achieve complete or partial remission, underscoring the importance of early diagnosis, precise histologic grading, and culturally responsive, evidence-based stewardship.