SLE — Systemic Pathology

Systemic lupus erythematosus (SLE) is the prototypic multisystem autoimmune disease driven by immune-complex deposition (type III hypersensitivity) plus some type II (antibody-mediated cytopenias) mechanisms. For Pathology, the examiner cares less about the rheumatology checklist and more about the organ-level morphology — the wire-loop lesion of lupus nephritis, Libman–Sacks endocarditis, serositis, and the haematoxylin (LE) body. This note is organised around what slides and one-liners are actually asked.

Definition & basic concept

SLE is a chronic, remitting–relapsing autoimmune disorder characterised by autoantibodies against nuclear antigens (ANA) leading to widespread immune-complex–mediated injury. It overwhelmingly affects women of reproductive age (F:M ≈ 9:1), with higher prevalence and severity in Afro-Caribbean and Asian populations. The unifying pathological mechanism is failure of clearance of apoptotic cell debris → exposure of nuclear antigens → autoantibody formation → immune complexes that deposit in vessels, glomeruli, skin and serosa, activating complement and recruiting neutrophils.

High-yield: SLE is the classic type III (immune-complex) hypersensitivity disease. The autoantibody–antigen complexes deposit in tissues; complement is consumed, so serum C3 and C4 fall during active disease (especially active nephritis).

Etiology & pathophysiology

The disease is multifactorial: genetic susceptibility + environmental triggers + hormonal milieu.

• Genetic: Strongest single link is hereditary deficiency of early complement components (C1q, C2, C4) — these are needed to clear apoptotic debris and immune complexes. HLA-DR2 and HLA-DR3 associations exist.
• Defective apoptotic clearance: Persistence of nuclear antigens (DNA, histones, ribonucleoproteins) drives autoantibody formation.
• Environmental: UV light (causes keratinocyte apoptosis and a photosensitive rash), drugs, and oestrogens.
• Immunological: TLR engagement by nucleic-acid–containing immune complexes → type I interferon (IFN-α) signature, B-cell hyperactivity, loss of T-cell tolerance.

Drug-induced lupus (DIL)

A favourite distractor. DIL is milder, lacks severe renal/CNS disease, and resolves on stopping the drug.

Feature	Classic SLE	Drug-induced lupus
Antibody	Anti-dsDNA, anti-Sm	Anti-histone (>95%)
Renal / CNS	Common, severe	Rare
Sex ratio	Strongly female	Near equal
Complement	Low (consumed)	Usually normal
Course	Chronic	Resolves on drug withdrawal

High-yield: Mnemonic for drugs causing DIL — "HIP-Q-MM": Hydralazine, Isoniazid, Procainamide, Quinidine, Methyldopa, Minocycline. Procainamide has the highest risk; hydralazine the most cases. Anti-histone antibody is the marker.

Autoantibodies — the immunology that pathology asks

Antibody	Sensitivity / Specificity	Clinical/path association
ANA	~95–99% sensitive, low specificity	Best screening test; if negative, SLE very unlikely
Anti-dsDNA	Specific; titres track disease	Lupus nephritis, disease activity
Anti-Smith (anti-Sm)	Most specific (but low sensitivity)	Diagnostic marker
Anti-histone	—	Drug-induced lupus
Anti-Ro (SSA)/La (SSB)	—	Neonatal lupus + congenital heart block, SCLE, Sjögren overlap
Anti-phospholipid (lupus anticoagulant, anti-cardiolipin, anti-β2GP1)	—	Thrombosis, recurrent fetal loss, false-positive VDRL, prolonged aPTT
Anti-ribosomal P	—	Lupus psychosis/CNS

High-yield: Anti-dsDNA and anti-Sm are the two most specific for SLE. Anti-dsDNA correlates with renal disease and activity; anti-Sm does not track activity. ANA is the screen, anti-dsDNA/anti-Sm confirm.

Antiphospholipid antibody paradox: they prolong the aPTT in vitro (lupus anticoagulant) yet cause thrombosis in vivo, and produce a biological false-positive VDRL/RPR.

The LE cell & haematoxylin (Gross) body — a NEET PG favourite

This is the single most "Pathology-flavoured" SLE fact.

• Antibodies against nuclear material (anti-histone/anti-DNP) bind exposed nuclei of damaged cells. The opsonised, homogeneous nuclear mass is phagocytosed.
• A phagocyte (neutrophil/macrophage) that has engulfed this denatured nuclear material = LE cell — it shows a large homogeneous purple-blue inclusion that pushes the host nucleus to the periphery.
• The free, extracellular, smudgy purple-staining nuclear mass seen in tissue is the haematoxylin body (Gross body) — it is the in vivo counterpart of the LE cell phenomenon and is the only histologically diagnostic lesion of SLE.

High-yield: Haematoxylin (Gross) body = in vivo LE cell phenomenon = the only pathognomonic histological finding in SLE. It is found in glomeruli, heart, lung, spleen and lymph nodes. The in-vitro LE cell test is now obsolete but still examined.

Lupus nephritis — the most tested organ

Renal involvement determines prognosis. Mechanism = immune-complex deposition (anti-dsDNA complexes) in mesangium and along the GBM, activating complement. The ISN/RPS 2003 classification (six classes) is high-yield.

Class	Name	Key morphology	IF pattern
I	Minimal mesangial	Normal LM; deposits only on IF/EM	Mesangial
II	Mesangial proliferative	Mesangial hypercellularity	Mesangial
III	Focal (<50% glomeruli)	Focal proliferation ± necrosis	Subendothelial
IV	Diffuse (≥50%)	Most common & most severe; wire-loop lesions, DPGN	Subendothelial, "full house"
V	Membranous	Diffuse GBM thickening, subepithelial deposits → nephrotic	Subepithelial
VI	Advanced sclerosing	≥90% globally sclerosed glomeruli	—

High-yield: Class IV (diffuse proliferative glomerulonephritis, DPGN) is the most common AND most severe form of lupus nephritis. It produces the wire-loop lesion and presents with nephritic/nephrotic features, hypertension and rising creatinine.

Wire-loop lesion — what it is

The wire-loop appearance is caused by massive subendothelial immune-complex deposition that markedly thickens the glomerular capillary wall, giving it a rigid, refractile, homogeneous "wire" look on H&E/PAS. It is most characteristic of Class IV (also seen in severe Class III).

High-yield: Wire-loop lesion = subendothelial immune-complex deposits in glomerular capillary walls, classically Class IV lupus nephritis. On IF, lupus nephritis shows a "full house" pattern — IgG, IgM, IgA, C3 and C1q all positive.

Approach to a lupus nephritis stem: Young woman + facial rash + proteinuria/active sediment → anti-dsDNA + low C3/C4 → renal biopsy for ISN/RPS class → if Class III/IV → induction immunosuppression. Flow: Suspicion → ANA screen → anti-dsDNA/anti-Sm + complement → biopsy → class-directed therapy.

Cardiac pathology — Libman–Sacks endocarditis

• Libman–Sacks (verrucous) endocarditis = sterile, fibrinous, small vegetations on heart valves.
• Vegetations are characteristically on BOTH surfaces of the valve leaflets and on adjacent endocardium — this distinguishes them from infective and rheumatic vegetations.
• Mitral and aortic valves most often involved; usually clinically silent but can embolise.
• Antiphospholipid antibodies increase the risk and severity.

High-yield: Libman–Sacks vegetations occur on BOTH sides of the valve leaflet and are sterile. Compare: rheumatic = small warty vegetations along lines of closure; infective = large, friable, on atrial surface of mitral / ventricular surface of aortic; NBTE (marantic) = bland, on lines of closure, in cachexia.

Other cardiac involvement: pericarditis (commonest cardiac lesion overall — part of serositis), myocarditis, and accelerated coronary atherosclerosis (a leading cause of late death).

Serositis — pleura & pericardium

Immune-complex deposition on serosal surfaces produces fibrinous pleuritis and pericarditis with effusions. Pleuritic chest pain and a pericardial rub are common. Chronic disease → fibrous adhesions. Serositis is one of the classification criteria.

Skin & vessels

• Acute cutaneous lupus: the malar ("butterfly") rash sparing the nasolabial folds; photosensitive.
• Histology: vacuolar (liquefactive) degeneration of the basal layer, dermal oedema, perivascular lymphocytic infiltrate; immunoglobulin + C3 deposition at the dermo-epidermal junction = the "lupus band test" on direct immunofluorescence.
• Discoid lupus: follicular plugging, hyperkeratosis, scarring.
• Vasculitis: small-vessel leukocytoclastic vasculitis; Raynaud phenomenon is common.

High-yield: Lupus band test = granular IgG/C3 deposition along the dermo-epidermal junction — positive in lesional and non-lesional skin in SLE.

Other organs & vessels

• Joints: non-erosive synovitis; Jaccoud arthropathy (reducible deformities without erosion).
• Spleen: "onion-skin" (concentric perivascular fibrosis) of penicilliary arterioles — a classic descriptor.
• CNS: small-vessel vasculopathy, microthrombi (often APLA-related) → seizures, psychosis (anti-ribosomal P).
• Haematology: Coombs-positive haemolytic anaemia, leucopenia, lymphopenia, thrombocytopenia — these are type II mechanisms.

High-yield: "Onion-skin" perivascular fibrosis of splenic central arteries is a buzzword for SLE.

Diagnosis & investigations

• Screening: ANA by indirect immunofluorescence (homogeneous/rim pattern). Highly sensitive — a negative ANA makes SLE very unlikely.
• Confirmatory/specific: anti-dsDNA and anti-Sm.
• Disease activity: rising anti-dsDNA titre + falling C3/C4 = active disease, especially nephritis.
• Renal: urinalysis (active sediment, proteinuria), and biopsy is investigation of choice to classify nephritis (ISN/RPS).
• Classification criteria: historically the ACR criteria (mnemonic "SOAP BRAIN MD"); the newer 2019 EULAR/ACR criteria require a positive ANA as an entry criterion plus weighted clinical/immunological items.

Mnemonic — SOAP BRAIN MD: Serositis, Oral ulcers, Arthritis, Photosensitivity, Blood disorders, Renal, ANA, Immunological (anti-dsDNA/Sm/APLA), Neurological, Malar rash, Discoid rash.

Management / drug of choice (pathology-relevant essentials)

• All SLE patients: hydroxychloroquine (reduces flares, improves survival) + sun protection.
• Mild disease/flares: NSAIDs, low-dose glucocorticoids.
• Severe / proliferative lupus nephritis (Class III/IV): induction with corticosteroids + cyclophosphamide OR mycophenolate mofetil (MMF); MMF and belimumab/voclosporin increasingly used. Maintenance with MMF or azathioprine.
• Antiphospholipid syndrome with thrombosis: lifelong warfarin anticoagulation.

High-yield: Hydroxychloroquine is the backbone for every SLE patient. For severe lupus nephritis, cyclophosphamide or MMF is the induction agent.

Complications

• Renal failure from progressive lupus nephritis (Class IV → VI).
• Accelerated atherosclerosis → premature MI (a top cause of late mortality).
• Infection — leading cause of death overall, compounded by immunosuppression.
• Antiphospholipid syndrome: arterial/venous thrombosis, recurrent miscarriage.
• Neonatal lupus / congenital heart block from transplacental anti-Ro/La.
• Thrombocytopenia, haemolysis; rarely lupus pneumonitis, pulmonary haemorrhage.

High-yield: Bimodal mortality in SLE — early deaths from active disease and infection; late deaths from accelerated coronary atherosclerosis.

Key differentials

Condition	Distinguishing point
Mixed connective tissue disease	High-titre anti-U1-RNP; overlap features
Drug-induced lupus	Anti-histone, resolves on drug stop, spares kidney/CNS
Sjögren syndrome	Sicca + anti-Ro/La, focal lymphocytic sialadenitis
Systemic sclerosis	Anti-Scl-70 / anti-centromere, skin fibrosis
Rheumatoid arthritis	Erosive arthritis, anti-CCP/RF
Other immune-complex GN (post-strep, MPGN)	Different IF/EM; SLE shows "full house"

Recently asked / exam angle

NEET PG and INI-CET tend to recycle these:

• "Wire-loop lesion is seen in which class of lupus nephritis?" → Class IV (diffuse proliferative).
• "In vivo LE cell is called?" → Haematoxylin (Gross) body, the only pathognomonic histological lesion.
• Vegetations on both surfaces of the valve → Libman–Sacks endocarditis.
• Most specific antibody for SLE → anti-Sm; antibody correlating with nephritis/activity → anti-dsDNA.
• "Full house" immunofluorescence → lupus nephritis.
• Antibody in drug-induced lupus → anti-histone (commonest culprit drug = procainamide highest risk, hydralazine most cases).
• Onion-skin lesion of splenic arteries → SLE.
• Antiphospholipid antibody → prolongs aPTT in vitro, causes thrombosis in vivo, false-positive VDRL.
• Neonatal heart block → maternal anti-Ro/La.
• Investigation of choice to classify lupus nephritis → renal biopsy.

Rapid revision

1. SLE = type III immune-complex disease; young women; ANA screen, anti-dsDNA + anti-Sm specific.
2. Anti-dsDNA tracks activity/nephritis; anti-Sm is most specific but doesn't track activity.
3. Active disease → low C3/C4 (complement consumed).
4. Haematoxylin (Gross) body = in vivo LE cell = only pathognomonic histology.
5. Class IV DPGN = most common + most severe lupus nephritis; produces the wire-loop lesion.
6. Wire-loop = subendothelial immune-complex deposits; IF shows "full house" (IgG/IgM/IgA/C3/C1q).
7. Libman–Sacks endocarditis = sterile vegetations on BOTH valve surfaces (mitral/aortic).
8. Pericarditis is the commonest cardiac lesion; serositis affects pleura + pericardium.
9. Lupus band test = IgG/C3 at the dermo-epidermal junction (lesional + non-lesional skin).
10. Drug-induced lupus = anti-histone; procainamide/hydralazine; spares kidney/CNS, reversible.
11. Onion-skin perivascular fibrosis of splenic arterioles = SLE buzzword.
12. Hydroxychloroquine for all; cyclophosphamide/MMF for severe (Class III/IV) nephritis; renal biopsy is the IOC to classify.