Autoimmune Disorders

Pediatric Autoimmunity Overview - Tiny Troublemakers

• Immune system mistakenly targets self-antigens, leading to tissue damage; a failure of "self-tolerance."
• Pediatric onset: Often more aggressive, potentially affecting multiple organ systems.
• Etiology: Multifactorial.
  • Genetic susceptibility (e.g., HLA-DR, PTPN22).
  • Environmental triggers (infections like EBV, Strep; UV light).
  • Hormonal factors (pubertal changes).
• Pathogenesis: Involves T & B cell dysregulation, autoantibody production, molecular mimicry.
• Common examples: JIA, SLE, Type 1 DM, Celiac disease, Autoimmune hepatitis.

⭐ Antinuclear Antibody (ANA) is a frequently positive screening test in pediatric rheumatology, but its presence alone is not diagnostic and requires careful clinical correlation.

Juvenile Idiopathic Arthritis (JIA) - Joint Jamboree

• Chronic arthritis (> 6 weeks) in children < 16 years; diagnosis of exclusion. 📌 JIA = Juvenile Inflammation of Articulations.
• Key Subtypes (ILAR):
  • Oligoarticular: ≤4 joints. Most common. High uveitis risk if ANA+.
  • Polyarticular (RF- & RF+): ≥5 joints. Symmetric involvement common.
  • Systemic (Still's Disease): Arthritis, quotidian fever (spikes daily), evanescent "salmon-pink" rash.
  • Enthesitis-related: Arthritis & enthesitis (e.g., heel pain). HLA-B27 often +.
  • Psoriatic: Arthritis & psoriasis (or family history).
• Complications: Uveitis (screen!), growth disturbances, Macrophage Activation Syndrome (MAS) in Systemic JIA.
• Rx: NSAIDs, DMARDs (Methotrexate), Biologics (e.g., anti-TNF), Corticosteroids.

⭐ Oligoarticular JIA, ANA-positive, has highest risk of chronic anterior uveitis; regular eye exams crucial.

Pediatric SLE & JDM - Systemic Storms

• Pediatric Systemic Lupus Erythematosus (SLE)
  • Multisystem autoimmune; F:M ratio ~4.5:1 (prepubertal), ↑ to 8:1 (postpubertal).
  • 📌 SOAP BRAIN MD criteria (Serositis, Oral ulcers, Arthritis, Photosensitivity, Blood, Renal, ANA, Immunologic, Neurologic, Malar, Discoid).
  • Key Abs: ANA (sensitive), Anti-dsDNA (specific, nephritis marker), Anti-Sm (highly specific).
  • Tx: Corticosteroids, Hydroxychloroquine (HCQ); severe: Mycophenolate Mofetil (MMF), Cyclophosphamide.
• Juvenile Dermatomyositis (JDM)
  • Characteristic rash + proximal muscle weakness.
  • Skin: Heliotrope rash (eyelids), Gottron's papules (extensor surfaces), malar rash.
  • Muscle: Symmetrical proximal weakness; ↑CK, ↑Aldolase, ↑LDH.
  • Key Abs: Anti-Mi-2 (classic), Anti-MDA5 (ulceration, ILD), Anti-NXP2 (calcinosis).
  • Tx: Corticosteroids, Methotrexate; IVIG for severe/refractory.
  • 
• ⭐ > In JDM, Anti-MDA5 antibodies are associated with rapidly progressive interstitial lung disease (RP-ILD) and skin ulcerations.

Pediatric Vasculitides (Kawasaki & HSP) - Vessel Vandals

Kawasaki Disease (KD): Mucocutaneous Lymph Node Syndrome

• Acute febrile illness, medium vessel vasculitis.
• 📌 CRASH & Burn: Fever ≥5 days PLUS ≥4 of:
  • Conjunctivitis (bilateral, non-exudative)
  • Rash (polymorphous, non-vesicular)
  • Adenopathy (cervical, ≥1.5cm, usually unilateral)
  • Strawberry tongue, red/cracked lips
  • Hand/foot edema, erythema, periungual desquamation
• Complication: Coronary artery aneurysms (CAA). Echo vital.
• Treatment: IVIG (2g/kg) + high-dose Aspirin (ASA) (80-100mg/kg/day initially), then low-dose ASA.

Henoch-Schönlein Purpura (HSP) / IgA Vasculitis

• Most common childhood systemic vasculitis. Small vessels.
• Often post-URI.
• 📌 Classic Tetrad (PAAR):
  • Palpable purpura (buttocks, lower limbs; non-thrombocytopenic)
  • Arthritis/arthralgia (large joints, esp. ankles/knees)
  • Abdominal pain (colicky; risk of intussusception, GI bleed)
  • Renal involvement (hematuria/proteinuria; IgA nephropathy)
• Diagnosis: Clinical. Skin biopsy (if atypical): leukocytoclastic vasculitis, IgA deposition.
• Treatment: Supportive (hydration, analgesia). Corticosteroids for severe GI/renal involvement.

⭐ Kawasaki Disease is the leading cause of acquired heart disease in children in developed countries; timely IVIG reduces coronary aneurysm risk from ~25% to <5%.

High‑Yield Points - ⚡ Biggest Takeaways

• JIA: Most common pediatric rheumatic disease; oligoarticular often ANA+, risk of uveitis.
• SLE: Malar rash, nephritis, cytopenias; anti-dsDNA & anti-Sm are specific markers.
• Kawasaki Disease: Fever, conjunctivitis, rash, mucositis; risk of coronary artery aneurysms.
• IgA Vasculitis (HSP): Palpable purpura, arthritis, abdominal pain, nephritis.
• JDM: Proximal muscle weakness with Gottron's papules & heliotrope rash.
• Type 1 DM: Autoimmune destruction of pancreatic β-cells; linked to HLA-DR3/DR4.