Eosinophilic lung disease

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

Eosinophilic lung disease is a differential framework, not a single treatment label. Primary eosinophilic pneumonias are largely confined to the lung; EGPA and hypereosinophilic syndromes have systemic consequences; ABPA reflects fungal sensitisation in susceptible airways; parasites and medicines are secondary causes. The tempo, asthma history, absolute eosinophil count, organ involvement, imaging distribution and exposures narrow the field. A normal eosinophil count at one time point cannot safely end the assessment.

Acute eosinophilic pneumonia can mimic severe infection or ARDS, sometimes after a new smoking or inhalational exposure. Chronic eosinophilic pneumonia often produces peripheral upper-lobe-predominant consolidation and pronounced blood eosinophilia, but this pattern is not exclusive. EGPA is considered when late-onset or difficult asthma and sinonasal disease are joined by neuropathy, purpura, cardiac disease, pulmonary infiltrates or renal findings. ANCA may support a phenotype but is absent in many cases.

Treatment depends on cause and organ threat. Stop a causative medicine, treat relevant infection or parasite, and use systemic corticosteroids for significant primary eosinophilic pneumonia under specialist care. Organ-threatening EGPA needs urgent rheumatology-vasculitis management and may require additional induction therapy; benralizumab applies to the narrower relapsing or refractory population defined by NICE. Repeated steroid courses without classification invite toxicity and can conceal a dangerous systemic disorder.

Key points

Pulmonary eosinophilia means eosinophils are implicated in lung disease; the task is to identify whether disease is primary, vasculitic, allergic, parasitic or drug induced.
Acute eosinophilic pneumonia presents over days with fever, diffuse infiltrates and hypoxaemia; blood eosinophilia may be absent initially.
Chronic eosinophilic pneumonia usually evolves over weeks with cough, breathlessness, constitutional symptoms, asthma and peripheral-predominant air-space opacity.
EGPA combines eosinophilic inflammation with variable necrotising small-vessel vasculitis, often in an adult with asthma and chronic rhinosinusitis.
Cardiac involvement, mononeuritis multiplex, renal injury, gastrointestinal ischaemia or CNS disease makes suspected EGPA urgent regardless of the chest radiograph.
ABPA should be considered when asthma or bronchiectasis coexists with high total IgE, Aspergillus sensitisation, eosinophilia and mucus plugging or central bronchiectasis.
Build a medicine and travel timeline: daptomycin and other drugs can cause eosinophilic pneumonia, while helminth infection changes both diagnosis and steroid safety.
Bronchoalveolar lavage eosinophilia supports acute disease when peripheral counts lag, but lavage findings still require exclusion of infection and other causes.
Corticosteroid response is often dramatic yet not diagnostic; relapse after taper is more typical of chronic disease than a completely treated acute episode.
Benralizumab is a NICE-approved add-on option for eligible relapsing or refractory adult EGPA, delivered through specialist vasculitis services rather than general eosinophilic pneumonia care.

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

Primary eosinophilic pneumonia

Acute or chronic eosinophilic pneumonia may arise without an identified systemic disease, sometimes following a new or changed inhalational exposure.

Allergic airway disease

Asthma and allergic bronchopulmonary aspergillosis recruit eosinophils through type 2 pathways, with mucus impaction and bronchiectasis in ABPA.

Secondary reactions

Medicines, parasites, fungi and other infections can drive pulmonary eosinophilia, making travel, exposure and treatment timelines essential.

Systemic eosinophilic disease

Eosinophilic granulomatosis with polyangiitis and hypereosinophilic syndromes involve lung alongside nerves, skin, heart, kidneys or other organs.

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

1
Eosinophil recruitment
Type 2 cytokines and chemokines promote marrow production, bloodstream survival and migration of eosinophils into pulmonary tissue.
2
Granule-mediated injury
Activated eosinophils release cytotoxic proteins, lipids and oxidants that damage epithelium and increase vascular permeability, with effects that increase as the pathological process progresses.
3
Airway and alveolar inflammation
The response causes bronchospasm, mucus, interstitial thickening or alveolar filling according to the specific syndrome, with effects that increase as the pathological process progresses.
4
Systemic extension
In vasculitic or hypereosinophilic disease, vascular inflammation and cellular infiltration injure nerves, myocardium, kidneys and other organs.

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

Acute eosinophilic pneumoniaRed flag

Days of febrile respiratory illness, diffuse bilateral opacity, severe hypoxaemia and often pleural fluid occur in a previously healthy person; recent smoking or inhalational change may be reported.

Chronic eosinophilic pneumonia

Weeks of cough, breathlessness, fever, night sweats or weight loss occur commonly with asthma, blood eosinophilia and peripheral-predominant consolidation that may migrate.

EGPA phenotype

Adult asthma and chronic rhinosinusitis coexist with substantial eosinophilia plus neuropathy, purpura, migratory infiltrates, cardiac disease, gastrointestinal symptoms or renal involvement.

Cardiac or neurological vasculitisRed flag

Chest pain, heart failure, arrhythmia, syncope, foot or wrist drop, asymmetric painful neuropathy, seizures or encephalopathy in suspected EGPA requires emergency organ-specific assessment.

Drug-related eosinophilic pneumoniaRed flag

Cough, fever, dyspnoea and infiltrates begin after a plausible medicine, sometimes weeks into treatment; daptomycin is a recognised trigger and blood eosinophilia can initially be normal.

Parasitic or fungal context

Travel, soil exposure, raw food, immunosuppression or asthma with recurrent mucus plugging redirects testing toward helminths, fungal infection or ABPA before corticosteroid escalation.

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
Serial full blood count with differentialFirst step
Why
Quantify eosinophilia and observe its trajectory before treatment.
Interpretation and limitations
Use the absolute eosinophil count, not percentage alone. A normal early count does not exclude acute eosinophilic pneumonia, and corticosteroids can suppress eosinophils rapidly.
02
Chest radiograph and HRCT
Why
Define air-space distribution, severity and alternative diagnoses.
Interpretation and limitations
Diffuse oedema-like change favours acute disease; peripheral consolidation supports chronic eosinophilic pneumonia. Nodules, cavitation, embolic infarcts, mucus impaction or bronchiectasis alter the differential.
03
Bronchoscopy with lavage
Why
Demonstrate pulmonary eosinophilia and sample for infection in selected cases.
Interpretation and limitations
A high lavage eosinophil proportion supports eosinophilic pneumonia, especially when blood counts are normal, but fungi, mycobacteria and other infections must be addressed before immunosuppression.
04
Renal, liver, cardiac and urinalysis assessment
Why
Detect systemic organ involvement that changes urgency and treatment.
Interpretation and limitations
Haematuria, proteinuria, renal decline, troponin elevation, BNP change or hepatic abnormality may indicate vasculitis or another systemic cause and should not be attributed to uncomplicated pneumonia.
05
ANCA and phenotype-led autoimmune tests
Why
Support evaluation for EGPA or another vasculitis.
Interpretation and limitations
MPO-ANCA can support EGPA but is neither required nor sufficient; organ pattern and exclusion of mimics are decisive. Positive tests can also occur with drugs or infection.
06
Total IgE and Aspergillus sensitisation tests
Why
Evaluate ABPA in a compatible asthma or bronchiectasis phenotype.
Interpretation and limitations
Interpret total IgE, specific IgE or skin testing, eosinophils and imaging together. Sensitisation alone is common and does not establish allergic bronchopulmonary aspergillosis.
07
Travel, parasite and medicine investigations
Why
Identify a reversible secondary cause and prevent unsafe steroids.
Interpretation and limitations
Select stool, serology or infectious-disease testing from geography and exposure. Review every recent antimicrobial, anticonvulsant, anti-inflammatory and supplement with start and stop dates.

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

Bacterial or viral pneumonia

Fever and pulmonary opacities overlap; microbiology, exposure history and eosinophilic blood or lavage patterns help distinguish infection.

Allergic bronchopulmonary aspergillosis

Asthma, fungal sensitisation, high total IgE and central bronchiectasis identify ABPA within the wider eosinophilic differential.

Eosinophilic granulomatosis with polyangiitis

Neuropathy, purpura, renal or cardiac involvement and vasculitic features indicate systemic disease rather than isolated eosinophilic pneumonia.

Drug-induced pneumonitis

A compatible medicine timeline and improvement after supervised withdrawal support a secondary eosinophilic reaction, and corroborating objective findings prevent an incorrect diagnostic label.

Parasitic infection

Travel, ingestion and migration exposure with species-directed testing may reveal a helminthic cause that would be worsened by uncritical immunosuppression.

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

01Syndrome classificationFrom eosinophils to a causeFirst stepPulmonary infiltrates coexist with blood or lavage eosinophilia, or acute disease remains strongly suspected.

1Assess respiratory severity and systemic organ danger first, obtaining urgent cardiac, neurological or renal input when features suggest EGPA rather than isolated pneumonia.
2Map onset against asthma, sinonasal disease, new smoking, medicines, travel, parasites, fungal sensitisation and systemic symptoms; repeat the eosinophil count if initially normal.
3Use HRCT, lavage and cause-directed blood, urine and microbiology tests to distinguish acute or chronic eosinophilic pneumonia, EGPA, ABPA and secondary disease.
4Discuss uncertain or organ-threatening cases with respiratory, vasculitis, infectious-disease and radiology specialists before defining the long-term treatment label.

02Acute respiratory illnessStabilise before the label is completeDiffuse infiltrates and hypoxaemia progress over hours or days.

1Admit, give oxygen to the appropriate target and involve critical care early for severe gas-exchange failure or exhaustion.
2Send microbiology, review inhalational and drug exposures, and consider lavage when safe; remember that the first blood eosinophil count can be normal.
3Stop a likely offending medicine with the prescribing team and begin specialist corticosteroid treatment when eosinophilic pneumonia is sufficiently likely and infection has been addressed.
4Track oxygenation, imaging and eosinophils, and reassess promptly if the expected rapid clinical response does not occur.

03EGPAMatch treatment to organ threatAsthma and eosinophilia coexist with evidence of systemic vasculitic disease.

1Urgently define cardiac, neurological, renal, pulmonary, gastrointestinal and skin involvement, using organ-specific imaging and tests rather than ANCA status alone.
2For life- or organ-threatening disease, follow the commissioned vasculitis induction pathway with rheumatology and relevant organ specialists; benralizumab evidence does not cover this emergency role.
3For relapsing or refractory non-organ-threatening adult EGPA, assess NICE benralizumab eligibility alongside standard care and steroid-reduction goals.
4Monitor disease activity, asthma control, eosinophils, steroid exposure and treatment toxicity; give patients a clear relapse and emergency plan.

Key medicines and prescribing safety2 treatments · regimens, roles and cautions

Usually produces rapid control of primary eosinophilic pneumonia and forms part of standard care for EGPA.

Prednisolone

Dose depends on acute respiratory severity, chronic eosinophilic pneumonia relapse risk or EGPA organ threat; use a specialist daily induction and taper specified by the local respiratory or vasculitis protocol.

Obtain appropriate infection and parasite assessment first when feasible. Monitor glucose, blood pressure, mood, bone, eyes and infection; premature taper can cause chronic eosinophilic pneumonia relapse, while repeated empiricism may conceal systemic vasculitis.

Add-on to standard care for eligible relapsing or refractory eosinophilic granulomatosis with polyangiitis, aiming for remission and reduced oral corticosteroid exposure.

Benralizumab for eligible adult EGPA

The licensed EGPA dose is 30 mg by subcutaneous injection every four weeks, initiated by an experienced specialist; follow the current SmPC and NICE commissioning conditions.

Not studied as rescue treatment for life-threatening EGPA; reassess continuation if such manifestations develop. Hypersensitivity can occur, helminth infection requires attention, and response is formally reviewed under the NICE pathway.

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

Acute respiratory failure

Rapid diffuse alveolar eosinophilic inflammation can cause severe hypoxaemia and need for ventilatory support, creating an additional need for recognition and targeted treatment.

Relapsing disease

Chronic eosinophilic pneumonia and related syndromes may recur during treatment reduction, requiring diagnostic review and steroid-sparing planning.

Cardiac eosinophilic injury

Systemic eosinophilic infiltration can cause myocarditis, thrombosis or fibrosis with arrhythmia and heart failure, with severity determined by its extent and the patient's underlying reserve.

Neurological and renal damage

Vasculitic disease may produce mononeuritis, glomerulonephritis and irreversible organ loss if systemic involvement is missed, with severity determined by its extent and the patient's underlying reserve.

Treatment toxicity

Prolonged corticosteroid and immune therapy increases infection, metabolic and skeletal complications, and increasing the burden of otherwise local respiratory disease.

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

Trend oxygen requirement, respiratory rate and imaging closely during acute disease; failure to improve should reopen infection and alternative diagnoses.
Repeat absolute eosinophil counts in context, recognising rapid suppression after corticosteroids or benralizumab and the possibility of an initially normal value.
For chronic eosinophilic pneumonia, follow symptoms, pulmonary function and relapse through taper, while tracking cumulative steroid burden.
For EGPA, assess asthma, sinonasal disease, skin, nerve, renal, cardiac and gastrointestinal activity rather than monitoring eosinophils alone.
Use ECG, biomarkers, echocardiography or cardiac MRI through the specialist pathway when cardiac symptoms or disease have been identified.
Review infection, vaccination, bone protection, reproductive safety and laboratory requirements for every immunomodulatory regimen.

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

Blood eosinophils can lag

Acute eosinophilic pneumonia may begin with a normal peripheral count; repeating the differential and considering lavage can prevent false reassurance in severe compatible illness.

ANCA is a phenotype clue

Many patients with EGPA are ANCA-negative. A negative result cannot dismiss vasculitis when asthma, eosinophilia and organ features fit.

The chest may not be the greatest danger

Cardiac inflammation or mononeuritis multiplex can define prognosis and treatment urgency even when pulmonary infiltrates or hypoxaemia are modest.

Peripheral opacity is not exclusive

The classic photographic-negative description of chronic eosinophilic pneumonia is memorable but neither sufficiently sensitive nor specific to close the differential.

Steroids erase evidence quickly

If clinically safe, obtain eosinophil counts, microbiology and key samples before treatment because corticosteroids can normalise eosinophilia and obscure subsequent classification.

11Common pitfallsFrequent interpretation and management errors.

01
Excluding acute eosinophilic pneumonia because the first peripheral eosinophil count is normal.
02
Calling asthma plus eosinophilia EGPA without looking for vasculitic organ disease and secondary causes.
03
Starting corticosteroids before considering Strongyloides or another parasite in an exposure-relevant patient.
04
Treating ANCA as a binary rule-in or rule-out test for eosinophilic granulomatosis with polyangiitis.
05
Missing daptomycin or another newly started medicine because only long-term prescriptions were reviewed.
06
Using benralizumab as sole emergency therapy for life-threatening cardiac, neurological or renal EGPA.