7.2 Systemic Autoimmune & Vasculitic Diseases

7.2 Systemic Autoimmune & Vasculitic Diseases

Systemic autoimmune connective tissue diseases and vasculitides present multi-organ pathology requiring precise serological interpretation, prompt immunosuppressive escalation, and vigilance for life-threatening complications.

Systemic Lupus Erythematosus (SLE)

Diagnostic Criteria & Entry Standard

Under the 2019 EULAR / ACR Classification Criteria, an Antinuclear Antibody (ANA) titer of ≥1:80 on HEp-2 cells is the mandatory entry criterion. Once satisfied, clinical and immunological domains are scored. A total score of ≥10 points classifies SLE.

Autoantibody Panel & Clinical Correlations

• ANA: Sensitivity >95%. Highly sensitive screening tool, but low specificity.
• Anti-double-stranded DNA (anti-dsDNA): Sensitivity ~60–70%, Specificity ~95%. Levels correlate dynamically with disease activity and predict active Lupus Nephritis flares.
• Anti-Smith (anti-Sm): Sensitivity ~20–30%, Specificity ~99%. Pathognomonic for SLE; levels do not fluctuate with disease activity.
• Anti-Ro (SSA) & Anti-La (SSB): Associated with Subacute Cutaneous Lupus (SCLE), Sjögren syndrome, and transplacental IgG passage causing Neonatal Lupus and congenital complete heart block.
• Anti-ribosomal P: Specific for Neuropsychiatric Lupus (lupus psychosis, severe depression).
• Anti-U1-RNP: High titers are characteristic of Mixed Connective Tissue Disease (MCTD) (overlap of SLE, systemic sclerosis, and polymyositis).
• Serum Complements (C3, C4): Hypocomplementemia indicates active classical complement pathway consumption during active lupus flares.

Lupus Nephritis Staging & Management

Lupus nephritis affects up to 50% of SLE patients. Renal biopsy is essential:

• Class I: Minimal mesangial lupus nephritis.
• Class II: Mesangial proliferative lupus nephritis.
• Class III: Focal lupus nephritis (<50% of glomeruli involved).
• Class IV (Diffuse Proliferative): Most common and severe pattern (>50% glomeruli involved; wire-loop lesions on light microscopy). Requires immediate induction therapy with high-dose corticosteroids PLUS Mycophenolate Mofetil or IV Cyclophosphamide.
• Class V: Membranous lupus nephritis (severe nephrotic-range proteinuria).
• Class VI: Advanced sclerotic lupus nephritis (>90% sclerotic glomeruli).

Universal Rule: Every SLE patient without contraindications MUST receive long-term Hydroxychloroquine (200–400 mg/day, capped at <5 mg/kg actual body weight to prevent retinal toxicity), which reduces flares, organ damage accumulation, thrombotic risk, and overall mortality.

Antiphospholipid Syndrome (APS)

Diagnostic Sydney Criteria

Diagnosis requires at least 1 Clinical Criterion AND 1 Laboratory Criterion:

1. Clinical Criteria:
   • Vascular Thrombosis: ≥1 episode of arterial, venous, or small vessel thrombosis confirmed by imaging or histopathology.
   • Pregnancy Morbidity:
     • ≥3 unexplained consecutive spontaneous abortions <10th week of gestation, OR
     • ≥1 unexplained fetal loss ≥10th week of gestation (morphologically normal fetus), OR
     • ≥1 premature birth <34th week of gestation due to eclampsia, severe pre-eclampsia, or placental insufficiency.
2. Laboratory Criteria (Confirmed on ≥2 occasions at least 12 weeks apart):
   • Lupus Anticoagulant (LA): Prolonged phospholipid-dependent coagulation assay (APTT, dRVVT) that fails to correct with 1:1 normal plasma mix, but corrects upon adding excess phospholipids.
   • Anti-β₂-Glycoprotein I antibodies (IgG or IgM >99th percentile).
   • Anti-Cardiolipin antibodies (IgG or IgM medium/high titer >40 GPL/MPL).

Catastrophic Antiphospholipid Syndrome (CAPS)

Rapidly fatal microvascular thrombosis leading to organ failure in ≥3 organ systems within <1 week. Emergency Management: High-dose IV Corticosteroids + Therapeutic Anticoagulation (Heparin) + Plasma Exchange + IVIG.

Anticoagulation Management Protocols

• Primary Prevention (Asymptomatic positive antibodies): Low-dose Aspirin (75–100 mg daily).
• Secondary Prevention (Post-Venous Thromboembolism): Lifelong Warfarin targeted to an INR of 2.0–3.0.
• Arterial Thrombosis or Recurrent Venous Events on Warfarin: Warfarin targeted to an INR of 3.0–4.0 or INR 2.0–3.0 plus low-dose Aspirin.
• DOAC Warning: Direct Oral Anticoagulants (Rivaroxaban, Apixaban) are contraindicated in high-risk triple-positive APS due to significantly increased rates of arterial thrombotic events compared to Warfarin.
• Pregnancy in APS: Warfarin is teratogenic. Switch immediately to Therapeutic LMWH plus Low-dose Aspirin.

Systemic Sclerosis & Sjögren Syndrome

Systemic Sclerosis (Scleroderma)

Autoimmune vasculopathy, immune activation, and excessive collagen deposition leading to skin fibrosis and visceral organ disease.

                    Systemic Sclerosis Subtypes
                                 │
       ┌─────────────────────────┴─────────────────────────┐
       ▼                                                   ▼
[Limited Cutaneous (lcSSc)]                       [Diffuse Cutaneous (dcSSc)]
 • Skin: Distal to elbows/knees, face             • Skin: Proximal to elbows/knees, trunk
 • CREST Syndrome features                         • Rapid onset skin thickening
 • Autoantibody: Anti-Centromere (~70–80%)         • Autoantibodies:
 • Major Risk: Isolated Pulmonary Arterial           - Anti-Scl-70 (Anti-topoisomerase I; ILD)
   Hypertension (PAH late in disease)                - Anti-RNA Polymerase III (Renal Crisis)

• CREST Acronym: Calcinosis cutis, Raynaud phenomenon, Esophageal dysmotility, Sclerodactyly, Telangiectasias.
• Scleroderma Renal Crisis (SRC): Abrupt onset of malignant hypertension, acute kidney injury, oliguria, and microangiopathic hemolytic anemia. Almost exclusively seen in diffuse systemic sclerosis (anti-RNA polymerase III positive).
  • Emergency Management: Immediate introduction of short-acting ACE Inhibitors (oral Captopril) titrated aggressively. Continue ACE inhibitor even if serum creatinine initially rises.
  • STEROID WARNING: Moderate-to-high dose corticosteroids (Prednisolone >15 mg/day) are strictly contraindicated in diffuse cutaneous systemic sclerosis as they directly precipitate Scleroderma Renal Crisis!

Sjögren Syndrome

• Pathophysiology: Autoimmune lymphocytic infiltration and destruction of exocrine glands (lacrimal and salivary glands).
• Clinical Presentation: Keratoconjunctivitis sicca (dry eyes), Xerostomia (dry mouth), bilateral parotid gland enlargement, and systemic features (arthralgia, fatigue, interstitial nephritis).
• Diagnostic Evaluation:
  • Schirmer Test: Standardized filter paper placed in lower conjunctival sac; ≤5 mm wetting in 5 minutes indicates severe tear deficiency.
  • Autoantibodies: Anti-Ro/SSA (70%) and Anti-La/SSB (50%).
  • Minor Salivary Gland Biopsy: Focal lymphocytic sialadenitis with a Focus Score ≥1 focus per 4 mm² (a focus = collection of ≥50 lymphocytes).
• Malignancy Complication: Patients have a 15- to 20-fold increased risk of B-cell Non-Hodgkin Lymphoma (specifically MALT lymphoma of the parotid gland). Suspect lymphoma if persistent asymmetric parotid swelling, palpable purpura, monoclonal gammopathy, or sudden drop in C4 levels occurs.

Inflammatory Myopathies

Polymyositis (PM) vs. Dermatomyositis (DM)

Symmetrical, subacute, progressive proximal muscle weakness (shoulder girdle, hip flexors—difficulty rising from a chair, climbing stairs, or combing hair). Sensory examination is normal.

• Laboratory Profile: Markedly elevated Creatine Kinase (CK, 10–50x upper limit of normal), AST, ALT, LDH, and Aldolase.
• Electromyography (EMG): Triad of short, small-amplitude polyphasic motor unit action potentials, fibrillations, and complex repetitive discharges.
• Muscle Biopsy Distinctions:
  • Polymyositis: Endomysial inflammation with CD8+ T-lymphocytes invading non-necrotic muscle fibers.
  • Dermatomyositis: Perimysial and perivascular inflammation with CD4+ T-lymphocytes and B-cells, accompanied by characteristic perifascicular atrophy.

Dermatomyositis Cutaneous Signatures

• Gottron Papules: Erythematous/violaceous flat papules over the dorsal aspect of MCP and PIP joints (pathognomonic).
• Heliotrope Rash: Violaceous periorbital edema affecting upper eyelids.
• Shawl Sign & V-Sign: Erythematous rash across shoulders/upper back (shawl) or anterior neck/chest (V-sign).
• Mechanic's Hands: Hyperkeratosis, scaling, and painful fissuring along the lateral aspects of fingers.

Myositis Autoantibodies & Malignancy Risk

• Anti-Jo-1 (Histidyl-tRNA synthetase): Associated with Antisynthetase Syndrome (myositis, severe Interstitial Lung Disease, Raynaud phenomenon, fever, mechanic's hands).
• Anti-Mi-2: Classic dermatomyositis with prominent skin features and favorable response to corticosteroids.
• Anti-MDA5: Amyopathic dermatomyositis with rapidly progressive ILD and palmar cutaneous ulcerations.
• Malignancy Screening: Dermatomyositis carries a 3- to 6-fold increased risk of underlying adenocarcinoma (ovarian, breast, lung, gastric, nasopharyngeal carcinoma). Mandatory age-appropriate cancer screening (CT chest/abdomen/pelvis, mammography, pelvic US, endoscopy) is required at diagnosis.

Inclusion Body Myositis (IBM)

• Epidemiology: Most common inflammatory myopathy in patients >50 years old (male predominance).
• Clinical Pattern: Insidious, asymmetrical distal and proximal weakness targeting wrist flexors, finger flexors (deep flexors), and quadriceps femoris. Dysphagia occurs in 50%.
• Biopsy: Rimmed vacuoles containing ubiquitin and beta-amyloid inclusions.
• Treatment: Remarkably resistant to corticosteroids and immunosuppressive therapy.

Systemic Vasculitis Classification & Serology Matrix

Vasculitides are categorized by the Chapel Hill Consensus Conference based on predominant vessel size: