# Systemic Lupus Erythematosus: Pediatric Onset vs. Adult Onset

## Overview
SLE is a chronic, multisystem autoimmune disease characterized by autoantibody production and immune complex deposition. ~15-20% of SLE cases are diagnosed before age 18 (childhood-onset SLE, cSLE) cSLE is more aggressive than adult-onset SLE: higher rates of nephritis, CNS involvement, hematologic abnormalities, and damage accrual. Female predominance in both populations (adult 9:1; pediatric 4-5:1 before puberty, increases post-puberty) Racial disparities are striking: higher incidence and severity in Black, Hispanic, and Asian populations.

## Diagnosis

### Classification Criteria
**2019 EULAR/ACR Classification Criteria**: entry criterion of ANA >= 1:80, then additive scoring across clinical and immunologic domains; score >= 10 classifies as SLE. Clinical domains: constitutional, hematologic, neuropsychiatric, mucocutaneous, serosal, musculoskeletal, renal. Immunologic domains: antiphospholipid antibodies, complement (low C3/C4), SLE-specific antibodies (anti-dsDNA, anti-Smith) Same criteria apply to children and adults. Sensitivity ~96%, specificity ~93%.

### Key Autoantibodies

| Antibody | Sensitivity | Specificity | Clinical Association |
|----------|-------------|-------------|---------------------|
| ANA | ~95% | Low | Screening test; nearly universal in SLE |
| Anti-dsDNA | 60-70% | ~95% | Nephritis; correlates with disease activity |
| Anti-Smith | ~30% | ~99% | Highly specific for SLE |
| Anti-Ro/SSA | 30-40% | Moderate | Neonatal lupus, photosensitivity, SCLE |
| Anti-La/SSB | 10-15% | Moderate | Neonatal lupus, Sjogren overlap |
| Antiphospholipid Abs | Variable | Moderate | Thrombosis, pregnancy complications |
| Anti-ribosomal P | 10-20% | High | NPSLE, hepatitis (especially cSLE) |

**ANA**: sensitive (~95%) but not specific; nearly universal in SLE. **Anti-dsDNA**: specific for SLE (~95%); levels correlate with disease activity, especially nephritis. **Anti-Smith (anti-Sm)**: highly specific for SLE (~99%) but less sensitive (~30%) **Anti-Ro/SSA and anti-La/SSB**: associated with neonatal lupus, photosensitivity, subacute cutaneous lupus. **Antiphospholipid antibodies** (lupus anticoagulant, anticardiolipin, anti-beta-2 glycoprotein): thrombosis and pregnancy complications. **Anti-ribosomal P**: associated with neuropsychiatric lupus and hepatitis in cSLE.

### Complement
Low C3 and C4 levels indicate active disease (consumption by immune complexes) CH50 screens for total complement function. Homozygous complement deficiency (C1q, C2, C4) predisposes to early-onset SLE.

<image>Diagnostic approach to SLE showing EULAR/ACR 2019 classification criteria with weighted scoring across clinical and immunologic domains and key autoantibody profiles</image>

## Clinical Manifestations: Pediatric vs. Adult

### Mucocutaneous
**Malar (butterfly) rash**: spares nasolabial folds; present in ~60-80% of cSLE vs ~50% of adults. **Discoid lupus**: more common in adults; can cause permanent scarring and alopecia. **Photosensitivity**: common in both; requires rigorous sun protection. **Oral/nasal ulcers**: often painless; can be missed on exam. **Non-scarring alopecia**: diffuse or patchy; common during flares. **Raynaud phenomenon**: vasospasm of digits; more common in adults.

### Renal (Lupus Nephritis)
**cSLE**: 50-80% develop nephritis (vs 30-50% in adults) Earlier onset and more severe in cSLE; ISN/RPS Classification:; Class I: minimal mesangial; Class II: mesangial proliferative; Class III: focal proliferative (< 50% glomeruli); Class IV: diffuse proliferative (>= 50% glomeruli) — most common and most severe. Class V: membranous; Class VI: advanced sclerotic; Presentation: proteinuria, hematuria, hypertension, edema, rising creatinine; Urine sediment: RBC casts, dysmorphic RBCs; Renal biopsy is essential for classification and treatment guidance; 10-year renal survival has improved to >90% with modern therapy.

### Neuropsychiatric (NPSLE)
19 recognized NPSLE syndromes (ACR classification) More common in cSLE (20-40%) than adult SLE. Most common: cognitive dysfunction, headache, mood disorder, seizures, cerebrovascular disease. Serious manifestations: psychosis, transverse myelitis, cerebral vasculitis. Diagnosis is challenging: exclude infection, metabolic causes, medication effects. MRI, CSF analysis, neuropsychological testing as indicated. Anti-ribosomal P and antiphospholipid antibodies associated with NPSLE.

### Hematologic
Cytopenias are common and often the presenting feature in cSLE. **Autoimmune hemolytic anemia** (AIHA): Coombs-positive; more common in cSLE. **Leukopenia/lymphopenia**: lymphopenia <1000 is a classification criterion. **Thrombocytopenia**: can be severe; may be the presenting feature. **Antiphospholipid syndrome**: thrombosis risk in both populations.

### Musculoskeletal
Non-erosive polyarthritis is the most common manifestation of SLE across all ages. Jaccoud arthropathy: reducible deformities from ligament laxity (not erosive) Avascular necrosis (osteonecrosis): especially hip and knee; related to corticosteroid use.

### Cardiovascular
Pericarditis (most common cardiac manifestation); Libman-Sacks endocarditis (verrucous vegetations, usually on mitral valve); Accelerated atherosclerosis: major cause of late mortality in adult SLE; Myocarditis: rare but life-threatening.

## Treatment

### General Principles
**Hydroxychloroquine (HCQ)**: CORNERSTONE of SLE management at ALL ages. Reduces flares, damage accrual, thrombosis, and mortality. Continue during pregnancy (safe; reduces neonatal lupus risk) Dose: 5 mg/kg/day (max 400 mg/day) to minimize retinal toxicity risk. Annual ophthalmologic screening (OCT) after 5 years of use (or earlier if risk factors) Retinal toxicity risk: cumulative dose-dependent; irreversible if not detected early.

### Mild Disease (Skin, Joints, Serositis)
HCQ + NSAIDs; Low-dose prednisone for flares (target lowest effective dose); Topical steroids and calcineurin inhibitors for skin disease; Methotrexate or azathioprine for steroid-sparing.

### Moderate Disease
HCQ + moderate-dose corticosteroids (0.5 mg/kg/day) + steroid-sparing DMARD. Mycophenolate mofetil (MMF): increasingly first-line for maintenance. Azathioprine: safe in pregnancy; alternative maintenance agent. Belimumab (anti-BLyS/BAFF): approved as add-on therapy for adults and children >= 5 years; reduces flares and steroid use.

### Severe Disease (Nephritis Class III-V, CNS, Severe Cytopenias)
**Induction therapy**: Pulse IV methylprednisolone (1g x 3 days) followed by oral prednisone taper. MMF (preferred induction for many patients, especially Black and Hispanic patients per ALMS trial) OR. IV cyclophosphamide (Euro-Lupus protocol: 500 mg every 2 weeks x 6 doses; or NIH protocol: higher doses monthly x 6) **Maintenance therapy**: MMF or azathioprine. Continue HCQ. Taper steroids to lowest dose (goal: prednisone <= 5 mg/day or off) **Voclosporin**: calcineurin inhibitor approved for lupus nephritis in adults; added to MMF background; AURORA trial showed superior renal response. **Anifrolumab**: anti-type I interferon receptor; approved for moderate-severe adult SLE; not yet in pediatric indications but studied.

### Refractory Disease
Rituximab (anti-CD20): used off-label for refractory nephritis, refractory cytopenias, NPSLE; RCTs were negative but real-world evidence supports benefit. Cyclophosphamide for severe refractory disease. Plasma exchange for catastrophic antiphospholipid syndrome or TTP-like presentations. HSCT: investigational for severe refractory SLE. CAR-T cell therapy: emerging reports of durable remission in refractory SLE (KYV-101 and others)

<image>Treatment algorithm for lupus nephritis showing biopsy-guided classification-based management from induction through maintenance therapy with key differences in pediatric versus adult regimens</image>

## Monitoring and Disease Activity Assessment

### Disease Activity Scores
**SLEDAI-2K**: most widely used; composite score of 24 weighted items. **BILAG**: organ-specific; useful for clinical trials. **Physician Global Assessment (PGA)**: VAS scale.

### Routine Monitoring
CBC, CMP, ESR, CRP at every visit; Anti-dsDNA and complement levels (C3, C4) — correlate with activity; Urinalysis with microscopy at every visit (detect nephritis flares early); Spot urine protein/creatinine ratio; Lipid panel (cardiovascular risk), blood glucose (steroid effects); Bone density monitoring with chronic steroid use.

### Growth and Development in cSLE
Linear growth: impaired by active disease and corticosteroid use. Delayed puberty: may occur with active disease or cyclophosphamide. Monitor growth velocity, bone age, Tanner staging. Minimize steroid exposure; use steroid-sparing agents aggressively.

## Pregnancy and Reproductive Health
Pregnancy in SLE is high-risk: increased preeclampsia, preterm birth, flares. Pre-pregnancy: disease should be quiescent for >= 6 months; switch to pregnancy-safe medications. **Safe in pregnancy**: HCQ (continue!), azathioprine, low-dose prednisone, calcineurin inhibitors. **Contraindicated**: MMF (teratogenic — neural tube defects), methotrexate, cyclophosphamide, belimumab (insufficient data) Anti-Ro/SSA positive women: risk of neonatal lupus (rash, congenital heart block); serial fetal echocardiograms from 16-26 weeks; HCQ reduces risk. Antiphospholipid syndrome in pregnancy: aspirin + LMWH prophylaxis. Fertility preservation: discuss before cyclophosphamide (gonadotoxic); GnRH agonist co-treatment may be protective.

## Clinical Pearls
Any child with unexplained cytopenias, nephritis, rash, or arthritis should have ANA checked — cSLE is often the unifying diagnosis. Hydroxychloroquine should essentially NEVER be discontinued in SLE — it reduces mortality, flares, damage, and thrombosis; compliance should be verified (serum HCQ levels available) cSLE patients with nephritis need renal biopsy — class guides treatment; do not treat empirically. Fatigue is the most common and most debilitating symptom reported by SLE patients — it is often undertreated and multifactorial (disease activity, depression, sleep disruption, deconditioning) Steroid use is the strongest modifiable predictor of damage accrual in SLE — strive for prednisone <= 5 mg/day (or off) in all patients. Adolescents with cSLE need proactive reproductive health counseling: effective contraception (avoid estrogen-containing OCPs if antiphospholipid antibodies positive), pregnancy planning, teratogenic medication management. CAR-T cell therapy represents a potential paradigm shift in refractory SLE — early data show deep, drug-free remission in selected patients.

## References
- Aringer M, Costenbader K, Daikh D, et al. 2019 EULAR/ACR Classification Criteria for Systemic Lupus Erythematosus. Arthritis Rheumatol. 2019;71(9):1400-1412.
- Harry O, Yasin S, Gideon B. Childhood-Onset Systemic Lupus Erythematosus: A Review and Update. J Pediatr. 2018;196:22-30.
- Fanouriakis A, Kostopoulou M, Cheema K, et al. 2019 Update of the Joint EULAR/ERA-EDTA Recommendations for the Management of Lupus Nephritis. Ann Rheum Dis. 2020;79(6):713-723.
- Rovin BH, Teng YKO, Ginzler EM, et al. Efficacy and Safety of Voclosporin versus Placebo for Lupus Nephritis (AURORA 1). Lancet. 2021;397(10289):2070-2080.