Connective-tissue-disease associated ILD

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

CTD-ILD is not one disease. The lung may show cellular inflammation, irreversible fibrosis, airway disease, pleural involvement or pulmonary vascular disease, sometimes in combination. The same HRCT pattern has different implications across systemic sclerosis, rheumatoid arthritis and inflammatory myopathy. A useful formulation names the systemic condition, radiological pattern, severity and behaviour—for example, systemic-sclerosis associated fibrotic NSIP with recent physiological progression—rather than stopping at 'autoimmune lung'.

Assessment is inherently multidisciplinary. Respiratory clinicians define physiology and imaging, rheumatology establishes systemic phenotype and treatment priorities, and radiology identifies pattern and progression. Autoantibody tests are chosen and interpreted in clinical context; a broad panel can generate incidental positives, whereas carefully sought clinical signs may reveal an antisynthetase or scleroderma phenotype. Some patients remain classifiable only as autoimmune-featured ILD and require longitudinal reassessment.

Management distinguishes reversible inflammatory activity from established progressive fibrosis while respecting disease-specific hazards. Immunomodulatory choices such as mycophenolate are specialist and often indication-dependent or off-label. Nintedanib has a licensed role in systemic-sclerosis ILD and progressive fibrosing ILD, subject to NICE and local criteria. Supportive respiratory care and management of reflux, aspiration, pulmonary hypertension, cardiac disease and muscle weakness are not optional add-ons.

Key points

Connective-tissue disease may precede ILD, appear concurrently or emerge after lung disease, so absence of a previous rheumatology diagnosis is not exclusion.
Systemic sclerosis, rheumatoid arthritis, inflammatory myopathy, Sjögren disease, mixed connective-tissue disease and lupus produce different patterns and risks.
Ask about Raynaud phenomenon, digital ulcers, skin tightening, inflammatory joints, sicca, dysphagia, reflux, photosensitive rash, proximal weakness and mechanic's hands.
NSIP is a common CTD-ILD pattern; UIP is especially important in rheumatoid arthritis, while organising pneumonia and lymphoid interstitial pneumonia occur in selected contexts.
Serology supports a clinically coherent phenotype but does not replace examination, HRCT interpretation or multidisciplinary discussion.
Rapidly progressive myositis-associated ILD can deteriorate over days to weeks even when muscle symptoms or creatine kinase elevation are limited.
Before escalating immunosuppression, consider bacterial, viral, fungal and opportunistic infection, particularly after corticosteroids or multiple agents.
In systemic sclerosis, corticosteroid exposure—especially higher doses—requires specialist caution because of scleroderma renal crisis risk.
Treatment targets inflammatory activity, fibrosis or both; the connective-tissue disease, HRCT behaviour, physiology and comorbidities determine the regimen.
Joint respiratory-rheumatology follow-up should track lung function, extrapulmonary activity, drug toxicity, vaccination, infection prevention and reproductive planning.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Systemic sclerosis

Autoimmune vascular and fibroblast activation commonly affects lung interstitium, often alongside reflux, pulmonary vascular disease and other systemic manifestations.

Inflammatory myopathy

Dermatomyositis, polymyositis and antisynthetase-spectrum disease can produce organising, non-specific interstitial or rapidly progressive lung injury, sometimes before obvious muscle weakness.

Rheumatoid and other autoimmune disease

Rheumatoid arthritis, Sjögren syndrome, lupus and mixed connective-tissue disease generate varied inflammatory or fibrotic ILD patterns.

Medicine and exposure interaction

Immunomodulators, infection, smoking and occupational exposures can mimic, precipitate or compound lung disease attributed to systemic autoimmunity.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Immune-mediated epithelial injury
Autoantibodies, lymphocytes and innate immune pathways injure alveolar epithelium and pulmonary microvasculature in a susceptible host.
2
Interstitial inflammation
Inflammatory cells and oedema thicken alveolar walls, reducing compliance and diffusion before substantial fibrosis is established.
3
Aberrant repair
Persistent injury activates fibroblasts and extracellular-matrix deposition, producing reticulation, traction bronchiectasis and sometimes honeycombing, and the downstream physiological effect determines clinical severity.
4
Gas-transfer impairment
Thickened or destroyed gas-exchange units cause exertional desaturation, while coexisting pulmonary hypertension or muscle weakness may amplify breathlessness.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Systemic sclerosis phenotype

Raynaud phenomenon, puffy fingers or sclerodactyly, digital ulcers, telangiectasia, reflux and dysphagia accompany basal NSIP or UIP-pattern fibrosis. Pulmonary arterial hypertension may coexist or dominate symptoms.

Rheumatoid arthritis lung disease

Established or evolving inflammatory polyarthritis can associate with UIP, NSIP, organising pneumonia, pleural disease, nodules and airway disorders. Smoking and some medicines complicate causal interpretation.

Myositis and antisynthetase clues

Proximal weakness, dysphagia, mechanic's hands, Gottron papules, heliotrope rash, inflammatory arthritis or Raynaud phenomenon may accompany NSIP or organising pneumonia, sometimes with little muscle enzyme elevation.

Rapidly progressive inflammatory ILDRed flag

Escalating cough, dyspnoea and oxygen requirement over days or weeks with new ground glass or consolidation can occur in inflammatory myopathy and requires urgent specialist assessment.

Diffuse alveolar haemorrhageRed flag

Haemoptysis may be absent; falling haemoglobin, hypoxaemia and diffuse opacities with vasculitic renal or systemic findings demand emergency respiratory, renal and rheumatology coordination.

Pulmonary hypertension or cardiac involvementRed flag

Syncope, chest pain, oedema, disproportionate TLCO reduction or breathlessness unexplained by HRCT raises pulmonary vascular disease, myocarditis or ventricular dysfunction and warrants prompt evaluation.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Targeted connective-tissue history and examinationFirst step
Why
Define the systemic phenotype that gives lung findings meaning.
Interpretation and limitations
Inspect skin, nailfolds, hands and joints; assess proximal power, swallowing and sicca features. Subtle or historical Raynaud phenomenon may be more informative than an isolated autoantibody.
02
HRCT chest
Why
Characterise ILD pattern, extent and competing pathology.
Interpretation and limitations
NSIP commonly shows basal ground glass and fine reticulation with traction change; UIP, organising pneumonia, LIP and mixed patterns occur. Compare serial imaging only with attention to technique and interval.
03
Spirometry, lung volumes and TLCO
Why
Quantify severity and detect progression.
Interpretation and limitations
A falling FVC can reflect progressive ILD, while a disproportionately low TLCO may signal pulmonary hypertension, emphysema or anaemia. Muscle weakness can reduce volumes without parallel radiological fibrosis.
04
Autoantibodies and muscle enzymes
Why
Support classification and identify high-risk systemic associations.
Interpretation and limitations
Use ANA pattern, ENA, rheumatoid markers, myositis-specific testing, creatine kinase and other tests according to phenotype and local laboratory pathways. Negative enzymes do not exclude amyopathic inflammatory myopathy.
05
Full blood count, renal, liver and inflammatory markers
Why
Identify organ involvement, infection clues and treatment baseline.
Interpretation and limitations
Cytopenia, eosinophilia, renal injury or transaminitis may redirect diagnosis and affect medicine safety. Inflammatory markers are nonspecific and may be blunted by immunosuppression.
06
Echocardiography, ECG and cardiac biomarkers
Why
Screen when cardiac disease or pulmonary hypertension is suspected.
Interpretation and limitations
An echocardiogram estimates probability rather than proving pulmonary hypertension; specialist right-heart catheterisation or cardiac MRI may be required after multidisciplinary review.
07
Microbiology and bronchoalveolar lavage when indicated
Why
Exclude infection or haemorrhage before major treatment escalation.
Interpretation and limitations
Sampling is tailored to immune status and imaging. A differential cell count is supportive rather than diagnostic; progressively bloodier lavage aliquots can support alveolar haemorrhage in the correct context.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Idiopathic interstitial pneumonia

An identical radiological pattern may occur without systemic disease; clinical phenotype, targeted serology and longitudinal review determine whether autoimmunity is causal.

Drug-induced lung disease

A compatible temporal relationship with methotrexate, biologics or other medicines and improvement after withdrawal may indicate toxicity rather than autoimmune progression.

Opportunistic infection

Fever, acute ground-glass change and immune suppression demand microbiological assessment because infection can closely mimic an inflammatory flare.

Pulmonary oedema

Cardiac or renal involvement can cause hydrostatic bilateral opacities; haemodynamics and response to volume management help distinguish them from ILD activity.

Chronic hypersensitivity pneumonitis

Bird, mould or occupational antigen exposure with air trapping or characteristic distribution supports exposure-driven disease despite positive low-specificity autoantibodies.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01Case findingConnect the lung and systemic phenotypeFirst stepILD is found in known connective-tissue disease or autoimmune clues appear in unexplained ILD.

1AlternativeAssess oxygenation and tempo, obtain complete physiology and HRCT, and document medication, infection, smoking and exposure histories that could provide alternative explanations.
2Perform a directed rheumatological examination and phenotype-led serology rather than treating a laboratory panel as a diagnosis.
3Discuss the case jointly with ILD radiology and rheumatology, naming pattern, extent, systemic disease confidence and whether inflammation or fibrosis appears dominant.
4Establish a shared monitoring plan and tell the patient which team to contact for respiratory decline, systemic flare or treatment toxicity.

02Rapid declineEscalate without missing infectionEscalationBreathlessness, physiology or oxygen need deteriorates substantially over days to weeks.

1Admit or urgently assess according to severity, support oxygenation, send early microbiology and investigate embolic, cardiac, aspiration and drug-related causes in parallel.
2Review immunosuppressive exposure and opportunistic infection risk; involve microbiology or infectious diseases when empirical treatment or invasive sampling is being considered.
3EscalationSeek rapid respiratory-rheumatology consensus on inflammatory ILD, alveolar haemorrhage or systemic vasculitis and agree any corticosteroid or immunosuppressive escalation through the acute local protocol.
4Monitor gas exchange, haemoglobin, renal function, imaging and treatment response closely, with early critical-care and treatment-ceiling discussion if the trajectory remains adverse.

03Chronic treatmentMatch therapy to disease behaviourCTD-ILD is clinically important, symptomatic or objectively progressing.

1Decide whether the priority is inflammatory control, antifibrotic treatment, systemic disease control or a combination, using serial physiology, HRCT and extrapulmonary activity.
2Select specialist therapy with explicit discussion of evidence, licensing, fertility, pregnancy, vaccination, infection risk and required laboratory monitoring.
3In systemic sclerosis, minimise avoidable corticosteroid exposure and monitor blood pressure and renal function closely whenever steroids are judged necessary.
4Return progressive fibrotic disease to MDT for NICE nintedanib eligibility, research or transplant consideration while continuing rehabilitation, oxygen and symptom care.

Key medicines and prescribing safety3 treatments · regimens, roles and cautions

Steroid-sparing immunomodulation for selected inflammatory or progressive CTD-ILD, particularly systemic-sclerosis associated disease.

Mycophenolate mofetil

A specialist often titrates from a low oral dose towards a locally agreed divided maintenance regimen; exact dosing, formulation and off-label indication must follow rheumatology or ILD protocol and current BNF advice.

Check full blood count, renal and liver function; counsel regarding serious infection, gastrointestinal effects and skin-cancer precautions. It is teratogenic, needs robust reproductive counselling and should not be started or altered without specialist supervision.

Antifibrotic therapy intended to slow lung-function decline rather than treat systemic autoimmune inflammation.

Nintedanib

For licensed adult SSc-ILD or eligible progressive fibrosing ILD, specialist initiation is generally 150 mg orally twice daily with food; use interruption or 100 mg twice daily for adverse effects under the SmPC.

Monitor liver function and gastrointestinal tolerance. Consider bleeding, arterial thrombotic and gastrointestinal perforation risks, hepatic impairment, pregnancy and drug interactions; combining with immunosuppression requires coordinated specialist oversight.

Rapid anti-inflammatory treatment for selected active organising pneumonia, myositis-associated ILD or vasculitic manifestations while longer-term therapy is planned.

Prednisolone in selected inflammatory disease

Dose and taper vary greatly by CTD phenotype, organ threat and infection risk; use the lowest effective specialist-prescribed regimen and verify the current local pathway rather than applying an ILD-wide dose.

Exclude or cover serious infection as clinically appropriate and monitor glucose, blood pressure, bone and mental-health effects. Higher-dose exposure can precipitate scleroderma renal crisis, so systemic sclerosis requires particular specialist caution.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Progressive pulmonary fibrosis

Continuing matrix deposition reduces lung volumes, gas transfer and exercise capacity despite control of some systemic inflammatory features.

Acute respiratory deterioration

Rapid inflammatory progression, acute exacerbation, infection or treatment toxicity can produce severe hypoxaemia and require urgent multidisciplinary distinction.

Pulmonary hypertension

Fibrotic vascular loss, hypoxic vasoconstriction or primary autoimmune vasculopathy can raise pulmonary pressures and cause right-heart failure.

Treatment-related infection

Immunosuppression increases bacterial, viral and opportunistic infection risk, which may present with the same symptoms as active ILD.

Respiratory muscle failure

Inflammatory myopathy can weaken inspiratory, expiratory and bulbar muscles, adding hypoventilation, ineffective cough and aspiration to parenchymal disease.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Track cough, dyspnoea, functional capacity, oxygen saturation and extrapulmonary symptoms at coordinated respiratory-rheumatology reviews.
Repeat FVC and TLCO every three to six months during early systemic sclerosis or active disease, then adjust to stability and the local guideline.
Re-image when symptoms or physiology worsen unexpectedly, not by automatic frequent CT schedules that add radiation without a decision point.
Monitor full blood count, renal and liver indices at the medicine-specific frequency, with additional infection and pregnancy-safety review where relevant.
In systemic sclerosis, measure blood pressure and renal function promptly with headache, visual symptoms or steroid exposure because renal crisis requires urgent recognition.
Screen for pulmonary hypertension or cardiac involvement when gas transfer, exercise capacity or symptoms decline out of proportion to parenchymal disease.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

The lung may present first

Inflammatory myopathy, rheumatoid arthritis or systemic sclerosis can declare itself after ILD. Repeat focused systemic assessment when new features emerge rather than permanently labelling disease idiopathic.

NSIP describes pattern, not cause

A basal NSIP appearance should trigger autoimmune and exposure thinking but can also be idiopathic or drug related; clinical synthesis remains essential.

Normal creatine kinase is not exclusion

Clinically amyopathic dermatomyositis can produce severe, rapidly progressive ILD with minimal muscle weakness and without a striking enzyme rise.

FVC has confounders

Respiratory muscle weakness, pleural disease, obesity and test effort alter vital capacity. Pair serial physiology with HRCT, TLCO and functional change.

Systemic sclerosis changes steroid calculus

A corticosteroid regimen tolerated in another inflammatory ILD may be hazardous in systemic sclerosis; renal-crisis risk makes disease-specific judgement indispensable.

11Common pitfallsFrequent interpretation and management errors.

01
Calling ILD idiopathic after a negative ANA alone without directed history, examination or appropriate phenotype-led testing.
02
Escalating immunosuppression for new ground-glass opacity before assessing opportunistic infection and cardiogenic oedema.
03
Using high-dose corticosteroids casually in systemic sclerosis without recognising renal-crisis risk.
04
Attributing disproportionate dyspnoea solely to fibrosis and missing pulmonary hypertension, myocarditis, anaemia or muscle weakness.
05
Allowing respiratory and rheumatology teams to monitor the same patient independently without a shared treatment and laboratory plan.
06
Assuming antifibrotic treatment controls joints, skin or inflammatory alveolitis; it addresses fibrotic progression, not the systemic disease.