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Systemic lupus erythematosus (SLE)
SLE is a multisystem autoimmune disease that almost always starts with a positive ANA; anti-dsDNA and anti-Sm are the specific antibodies, and hydroxychloroquine is given to every patient as the base of treatment.
Why it matters in the exam
A typical question presents a young woman with a rash over the cheeks that spares the folds between nose and lip, sun sensitivity, mouth ulcers, joint pain without destruction, a pleural effusion and low blood counts, and asks for the next test. Under the 2019 EULAR/ACR criteria an ANA titre of at least 1:80 is the entry condition, after which points are collected from clinical and immunological domains — 10 points or more classify SLE. Remember that anti-dsDNA and low C3 and C4 reflect activity, especially kidney inflammation, and that in a lupus flare the ESR rises while the CRP usually stays normal — a high CRP points to infection or serositis.
Other themes recur: drug-induced lupus (hydralazine, procainamide, isoniazid, minocycline, anti-TNF) with anti-histone antibodies and no kidney or brain involvement; antiphospholipid syndrome with thrombosis or recurrent miscarriage, where warfarin is preferred over a DOAC; and anti-Ro antibodies in pregnancy, which put the fetus at risk of congenital heart block. In treatment: hydroxychloroquine for all patients with periodic retinal checks, steroids at the lowest possible dose (prednisone 5 mg or less for maintenance), and immunosuppressants or biologics (belimumab, anifrolumab) when the disease is active. Class III–IV nephritis is treated with mycophenolate or low-dose cyclophosphamide together with steroids.
Key points
- Entry condition: ANA 1:80 or more; 10 points or more classify SLE.
- Specific: anti-dsDNA and anti-Sm; low C3 and C4 in a flare.
- Hydroxychloroquine for every patient; steroids 5 mg or less for maintenance.
- Class III–IV nephritis: steroids + mycophenolate or cyclophosphamide.
- Antiphospholipid with thrombosis: warfarin; anti-Ro in pregnancy: fetal heart block.
Summary table
| Topic | Finding | Meaning | Exam note |
|---|---|---|---|
| Entry condition | ANA titre 1:80 or more | Without a positive ANA, SLE is not classified | ANA is sensitive but not specific |
| Specific antibodies | Anti-dsDNA, anti-Sm | Anti-dsDNA tracks activity and nephritis | Anti-Sm is the most specific |
| Activity | Low C3 and C4, high ESR | Flare | High CRP → look for infection |
| Drug-induced lupus | Hydralazine, procainamide, isoniazid, anti-TNF | Anti-histone; no kidney or brain | Resolves when the drug is stopped |
| Antiphospholipid | Lupus anticoagulant, anticardiolipin, anti-β2GPI | Thrombosis, recurrent miscarriage | Warfarin, not a DOAC, after thrombosis |
| Base treatment | Hydroxychloroquine for every patient | Reduces flares and mortality | Periodic retinal checks |
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Sources
- EULAR/ACR Classification Criteria for Systemic Lupus Erythematosus, 2019 — Entry criterion and weighted clinical and immunological domains
- EULAR recommendations for the management of systemic lupus erythematosus, 2023 — Hydroxychloroquine, glucocorticoid tapering, immunosuppressants and biologics
- Harrison's Principles of Internal Medicine, 21st edition (2022) — Systemic Lupus Erythematosus
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.