Lupus and the Connective Tissue Diseases

TL;DR. Systemic lupus erythematosus is the disease that can imitate almost anything. The immune system produces antibodies against the contents of the cell nucleus, those antibodies form complexes with their targets, and the complexes deposit in whatever tissue they reach: skin, joints, kidneys, blood cells, brain, the lining of the heart and lungs. Which organs are hit determines whether someone has a manageable illness of rashes and joint pain or a life-threatening one destroying their kidneys. It affects women roughly nine times more than men, strikes during the childbearing years, and is more common and more severe in people of African, Hispanic, and Asian ancestry. Five-year survival was about 50 percent in the 1950s and exceeds 90 percent at ten years now, and the single drug most responsible is one of the oldest and cheapest available.

Key takeaways

• Lupus affects roughly 3.4 million people, about 90 percent of them women, with onset typically between 15 and 45.
• Hydroxychloroquine is recommended for essentially every patient, indefinitely. It reduces flares, organ damage, clotting, and death, and it costs very little.
• Lupus nephritis affects up to 40 to 50 percent and is the main determinant of long-term outcome. It is silent early, which is why urine is tested at every visit.
• A positive ANA test does not mean lupus. Around 10 to 15 percent of healthy people have one, and the test is useful for ruling out rather than ruling in.
• Antiphospholipid syndrome causes clots and recurrent pregnancy loss, and it is the reason some patients need lifelong anticoagulation rather than immunosuppression.
• Systemic sclerosis has the highest mortality of the connective tissue diseases, and its most dangerous complications are in the lungs and, acutely, the kidneys.

Systemic lupus erythematosus

In short: Antibodies against your own cell nuclei, forming complexes that deposit anywhere, producing a disease that can look like almost any other.

What it is

Lupus is a chronic multisystem autoimmune disease characterised by antibodies against nuclear components: DNA, histones, and the protein-RNA complexes inside the nucleus.

The name is medieval and descriptive: lupus is Latin for wolf, applied to the facial rash because it was thought to resemble a wolf bite or a wolf's facial markings. Erythematosus means reddened. The butterfly or malar rash across the cheeks and bridge of the nose, characteristically sparing the folds beside the nose, is the classic sign and is present in fewer than half of patients.

Diagnosis uses classification criteria (EULAR/ACR 2019) requiring a positive ANA as an entry criterion, then weighted points across clinical and laboratory domains. In practice it is a pattern recognised over time, and the average patient sees several clinicians before it is made.

What actually goes wrong

The mechanism, in sequence:

1. Cells die and are not cleared properly. Normally, cells dying by apoptosis are rapidly engulfed and their contents never seen by the immune system (Chapter 3). In lupus, clearance is impaired, so nuclear material is exposed.
2. The immune system treats nuclear material as foreign. Because DNA and RNA are exactly what the innate immune system evolved to detect in viruses, sensors including toll-like receptors are triggered.
3. Type I interferon. This produces a sustained interferon response, and an interferon signature is measurable in the blood of most patients. It is why interferon given as a drug can induce a lupus-like illness, and why anifrolumab, which blocks the interferon receptor, works.
4. Autoantibodies are produced: against double-stranded DNA, Smith antigen, Ro, La, and many more.
5. Immune complexes form and deposit in small vessels and basement membranes, activating complement (Chapter 13) and drawing in inflammatory cells. This is why complement levels (C3, C4) fall during active disease, as they are consumed, which is a useful and slightly counterintuitive marker.
6. Whatever tissue the complexes land in becomes inflamed.

Genetics and triggers. Heritability is substantial, with over 100 associated loci. Rare complete deficiencies of early complement components (C1q, C4) cause lupus with very high penetrance, which is strong evidence for the clearance-failure model. Environmental triggers include ultraviolet light (which causes skin cell death and reliably triggers flares), Epstein-Barr virus, smoking, silica exposure, and certain drugs.

Drug-induced lupus is a distinct entity caused by hydralazine, procainamide, isoniazid, minocycline, and TNF inhibitors among others. It typically spares the kidneys and brain, is associated with anti-histone antibodies, and resolves when the drug stops.

What it does to the body

The reason lupus is called a great imitator:

Lupus nephritis is the pivotal complication. It is graded by biopsy into six classes, which determines treatment, and it is silent until advanced. This is why every visit includes a urine test for protein: catching nephritis early is the difference between preserved kidney function and dialysis.

The cardiovascular risk is easy to miss because of the age of the patients. Young women with lupus have a risk of myocardial infarction many times that of their peers, and a heart attack in a 30-year-old woman is not what anyone is looking for.

Is it deadly?

Survival has been transformed. Five-year survival was roughly 50 percent in the 1950s; ten-year survival now exceeds 90 percent in high-income settings.

Mortality now follows a bimodal pattern: early deaths from active disease and infection, and later deaths from cardiovascular disease and the accumulated damage of both the disease and its treatment. Infection, driven by immunosuppression, is a leading cause throughout.

Outcomes are substantially worse in people of African and Hispanic ancestry, in those with lower income, and in those with limited access to specialist care, and the contributions of biology and of access have not been fully separated.

Is it contagious?

No. Lupus cannot be transmitted. It clusters in families through shared genes, and the Epstein-Barr virus association is a trigger rather than a transmissible cause: almost everyone carries EBV and almost nobody develops lupus.

Who gets it

• Roughly 90 percent female, with onset usually between 15 and 45. The sex difference narrows in childhood-onset and late-onset disease.
• Ancestry matters substantially. Incidence and severity are higher in people of African, Hispanic, Asian, and Indigenous ancestry than in those of European ancestry, with more nephritis and worse outcomes. Genetic factors, socioeconomic factors, and healthcare access all contribute and have not been cleanly separated (Chapter 70).
• Family history, silica exposure, smoking, and certain drugs.

Treatment, and how it works

Hydroxychloroquine for essentially everyone, indefinitely. It alters lysosomal pH and interferes with toll-like receptor signalling, reducing the interferon response. It reduces flares, prevents organ damage, reduces clotting, improves survival, and is safe in pregnancy. Its main long-term concern is retinal toxicity, which is why annual eye screening is done after five years, and the risk at correct weight-based dosing is low. It is inexpensive. Stopping it is one of the commonest causes of a flare.

CAR-T cell therapy deserves specific mention. Small series of patients with severe refractory lupus treated with CD19-directed CAR-T cells, the technology developed for blood cancers (Chapter 26), have achieved drug-free remission with the immune system apparently resetting after B-cell depletion and repopulation. If this holds up in larger trials it is the most significant development in autoimmune disease in decades.

What the person can do

• Take hydroxychloroquine, permanently, including when you feel well.
• Protect yourself from UV rigorously: shade, clothing, high-factor sunscreen, and awareness that fluorescent lighting and window glass transmit some UVA.
• Attend for urine testing at every visit, because nephritis is silent.
• Do not smoke: it worsens lupus, reduces hydroxychloroquine effectiveness, and adds to an already raised cardiovascular risk.
• Treat cardiovascular risk actively, despite being young.
• Plan pregnancy. Conceive during a period of stable, well-controlled disease, switch to pregnancy-compatible drugs beforehand, and be tested for anti-Ro and antiphospholipid antibodies, which change monitoring.
• Get vaccinated before immunosuppression where possible, and avoid live vaccines during it.
• Report new symptoms rather than assuming they are lupus. Infection is a leading cause of death and can look like a flare.

Antiphospholipid syndrome

In short: Antibodies that make blood clot, causing thrombosis and pregnancy loss, and treated with anticoagulation rather than immunosuppression.

Antiphospholipid syndrome (APS) is an autoimmune clotting disorder defined by persistent antiphospholipid antibodies (lupus anticoagulant, anticardiolipin, or anti-beta2-glycoprotein I) plus a clinical event: thrombosis (venous, arterial, or small vessel) or pregnancy morbidity (recurrent early miscarriage, fetal death, or severe pre-eclampsia).

It occurs alone or alongside lupus, in roughly 30 to 40 percent of lupus patients by antibody positivity, though many never have an event.

Why it matters:

• It is an important and treatable cause of stroke in young people (Chapter 22) and of recurrent miscarriage.
• Treatment is anticoagulation, not immunosuppression. After a thrombosis, indefinite anticoagulation is usual. Notably, warfarin remains preferred over direct oral anticoagulants in high-risk (triple-positive) APS, because a randomised trial found more arterial events on rivaroxaban. This is one of the few remaining places where warfarin is clearly better.
• In pregnancy, aspirin plus low molecular weight heparin substantially improves live birth rates.
• Catastrophic APS is a rare emergency with widespread small-vessel thrombosis and multiorgan failure, with high mortality.

Don't be confused: "lupus anticoagulant" causes clotting, not bleeding. The name comes from a laboratory artefact: these antibodies prolong a clotting time in the test tube while promoting clot formation in the body. It is one of the most misleading names in medicine, and patients reasonably assume it means the opposite of what it does.

Sjögren's disease

In short: Immune destruction of the glands that produce tears and saliva, plus fatigue and pain that are frequently dismissed.

Sjögren's is an autoimmune disease targeting exocrine glands, principally lacrimal (tear) and salivary. It occurs alone (primary) or with another connective tissue disease (secondary, most often with rheumatoid arthritis or lupus). It affects women roughly nine times more often than men, usually presenting in middle age.

Symptoms: persistent dry eyes (gritty, burning) and dry mouth (difficulty swallowing dry food, speaking at length, dental decay accelerating because saliva is the mouth's main defence), plus profound fatigue and widespread pain, which patients frequently rate as more disabling than the dryness and which is routinely under-recognised.

Beyond the glands: joint pain, Raynaud's phenomenon, interstitial lung disease, renal tubular problems, peripheral neuropathy, and vasculitis.

The complication that defines follow-up: Sjögren's carries a substantially increased risk of non-Hodgkin lymphoma, on the order of 5 to 20 fold, arising from the chronically stimulated B-cell populations in the glands. Persistent parotid swelling, low complement, or cryoglobulins are warning features.

Diagnosis: anti-Ro (SSA) and anti-La (SSB) antibodies, tests of tear and saliva production, and sometimes a minor salivary gland biopsy from the lip.

Treatment is largely symptomatic: artificial tears and saliva, pilocarpine to stimulate secretion, careful and frequent dental care, hydroxychloroquine for joint and fatigue symptoms (with modest trial evidence), and immunosuppression for organ involvement. Several B-cell targeted agents are in trials, and there is currently no treatment that restores gland function.

Systemic sclerosis (scleroderma)

In short: Autoimmune fibrosis, hardening the skin and internal organs, with the highest mortality of the connective tissue diseases.

Systemic sclerosis combines three processes: small-vessel damage, immune activation, and excessive collagen deposition producing fibrosis. The name means hard skin, and the skin is the visible part of a systemic problem.

Two forms, and the distinction predicts what happens:

Features:

• Raynaud's phenomenon in nearly all patients, often the first sign by years (Chapter 64). Digital ulcers and, in severe cases, loss of fingertips.
• Skin thickening, progressing from puffy fingers to tight, bound-down skin, restricting hand function and producing a characteristic tightening around the mouth.
• Gastrointestinal involvement in most patients: reflux (often severe), difficulty swallowing, bloating, malabsorption from small intestinal bacterial overgrowth, and constipation.
• Interstitial lung disease, now the leading cause of death.
• Pulmonary arterial hypertension, requiring annual screening with echocardiography.
• Scleroderma renal crisis: abrupt severe hypertension with acute kidney failure, historically a death sentence and now treated with ACE inhibitors, one of the clearest single-drug transformations in rheumatology. High-dose corticosteroids increase the risk of it, which is why steroids are used cautiously in systemic sclerosis.

Treatment targets the organs rather than the disease as a whole: immunosuppression (mycophenolate, and nintedanib as an antifibrotic) for lung disease, vasodilators for Raynaud's and pulmonary hypertension, proton pump inhibitors for reflux, ACE inhibitors for renal crisis, and autologous stem cell transplantation in selected patients with severe early diffuse disease, which improves survival at the cost of significant treatment-related risk.

Localised scleroderma (morphea) is a different, skin-limited condition without internal organ involvement, and the shared name causes considerable and unnecessary alarm.

Idiopathic inflammatory myopathies

In short: Immune attack on muscle, causing weakness rather than pain, and one form is strongly linked to underlying cancer.

The presenting complaint is weakness, not pain: difficulty climbing stairs, rising from a chair, or lifting arms above the head. Muscle enzymes (creatine kinase) are usually markedly raised. Involvement of swallowing muscles and of the lungs (interstitial disease, particularly with anti-synthetase antibodies) determines severity.

Treatment is corticosteroids plus a steroid-sparing immunosuppressant, intravenous immunoglobulin in severe or refractory cases, and, in dermatomyositis, treatment of any underlying cancer.

Mixed and undifferentiated connective tissue disease

In short: Overlapping features that do not fit one box, which is common and does not mean nothing is wrong.

Mixed connective tissue disease combines features of lupus, systemic sclerosis, and myositis with high titres of a specific antibody (anti-U1-RNP). Raynaud's and swollen fingers are typical, and pulmonary hypertension is the main risk.

Undifferentiated connective tissue disease describes patients with autoantibodies and clinical features insufficient to classify. A proportion evolve into a defined disease over years, and most remain mild. It is a legitimate diagnosis rather than a failure of diagnosis, and it needs monitoring rather than aggressive treatment.

Interpreting the antibody tests

In short: ANA is a screening test with poor specificity, and a positive result in someone without symptoms is usually a false alarm.

This causes an enormous amount of unnecessary anxiety and referral.

The practical rule: an ANA should be ordered when there is a clinical reason to suspect a connective tissue disease, not as a general screening test in someone with fatigue. Ordered indiscriminately, it produces far more false positives than diagnoses.

What the person can do

In short: Sun protection, hydroxychloroquine, pregnancy planning, and knowing which new symptom needs urgent attention.

• Take hydroxychloroquine if you have lupus, indefinitely, and attend the annual eye check after five years.
• Protect against UV if you have lupus or dermatomyositis.
• Keep warm and stop smoking if you have Raynaud's, and report any fingertip ulcer promptly.
• Get reflux treated aggressively in systemic sclerosis, because it damages the oesophagus and contributes to lung disease through aspiration.
• Attend annual screening for pulmonary hypertension and lung disease in systemic sclerosis, and for lymphoma warning signs in Sjögren's.
• Look after your teeth meticulously in Sjögren's, because saliva is the mouth's main defence and its loss accelerates decay dramatically (Chapter 62).
• Plan pregnancy in advance, in every disease in this chapter.
• Know the emergencies: sudden severe hypertension with reduced urine output in systemic sclerosis (renal crisis), new neurological symptoms in lupus or APS, a fingertip turning black, and any fever while immunosuppressed.

Sources and notes

Lupus prevalence of approximately 3.4 million: Global Burden of Disease and systematic reviews; estimates vary widely with case definition. EULAR/ACR 2019 classification criteria: Aringer et al. Survival improvement from roughly 50 percent at 5 years in the 1950s: historical cohort comparisons reviewed in Doria et al. Hydroxychloroquine benefits: Canadian Hydroxychloroquine Study Group, NEJM, 1991, and subsequent observational data on damage and mortality. Type I interferon signature: Baechler et al., PNAS, 2003. Anifrolumab: TULIP trials, NEJM and Lancet Rheumatology, 2020. Belimumab: BLISS trials. Voclosporin: AURORA. CAR-T in refractory lupus: Mackensen et al., Nature Medicine, 2022, and Müller et al., NEJM, 2024. Complement deficiency and lupus penetrance: standard immunology. APS classification: revised Sapporo criteria and the 2023 ACR/EULAR criteria; rivaroxaban inferiority in triple-positive APS: Pengo et al., Blood, 2018. Sjögren's lymphoma risk: multiple cohort studies. Scleroderma renal crisis and ACE inhibitors: Steen et al., Annals of Internal Medicine, 1990. Nintedanib in systemic sclerosis ILD: SENSCIS, NEJM, 2019. Stem cell transplantation: ASTIS and SCOT trials. ANA positivity in healthy populations: Satoh et al., Arthritis & Rheumatism, 2012.

Open questions. Whether CAR-T therapy produces durable drug-free remission in lupus, and in whom, is the field's most important current question. Why these diseases overwhelmingly affect women is not fully explained. Attributing neuropsychiatric symptoms to lupus itself, as opposed to its treatment or to coincidence, remains genuinely difficult.

Next: the family of inflammatory arthritis that attacks the spine and the places where tendons meet bone. 👉