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OverviewAetiologyPathophysiologyClinical features and red flagsInvestigationsDifferential diagnosisManagementComplicationsMonitoring and follow-upSpecial situationsCommon pitfallsQuestionsSources
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Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.

Cryptogenic organising pneumonia

Respiratory · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

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Time-critical presentation

Organising pneumonia can occasionally produce rapidly progressive hypoxaemic respiratory failure. Admit urgently when oxygenation, respiratory effort or haemodynamics are compromised, and investigate severe infection, pulmonary embolism, oedema, diffuse alveolar haemorrhage and acute eosinophilic pneumonia. Do not give outpatient corticosteroids for an undifferentiated acute bilateral infiltrative illness; obtain early respiratory and critical-care input and treat time-critical alternatives.

Overview

Recognise organising pneumonia as a clinicoradiological syndrome, exclude secondary causes and infection, and use specialist corticosteroid treatment with relapse-aware monitoring.

Organising pneumonia is a response to alveolar injury rather than a unique aetiology. Loose connective-tissue plugs occupy distal airspaces while underlying architecture is relatively preserved, explaining why treatment can produce substantial improvement. The clinician first recognises the syndrome, then searches for a cause. Only after reasonable exclusion of medicines, connective-tissue disease, recent infection, radiation, cancer and other associations should the prefix cryptogenic be used.

Presentation often resembles community-acquired pneumonia, but symptoms evolve over several weeks, inflammatory markers may remain raised and consolidations persist or move despite antibiotics. HRCT distribution is frequently bilateral, peripheral or peribronchovascular. Bronchoscopy is useful when infection, malignancy or eosinophilic disease must be excluded. Transbronchial biopsy may establish organising pneumonia in an appropriate case, while surgical biopsy is reserved for consequential uncertainty after MDT review.

Aetiology

01

Idiopathic organising pneumonia

Cryptogenic disease is diagnosed when the characteristic clinicoradiological process remains unexplained after a careful search for secondary triggers.

02

Post-infective injury

Viral or bacterial lung injury can initiate an organising repair response that persists after active infection has resolved.

03

Autoimmune and inflammatory disease

Connective-tissue disease, inflammatory bowel disease and transplantation can produce a secondary organising pneumonia pattern, and its contribution is interpreted alongside the other recognised causes.

04

Medicines, radiation and inhalation

A range of drugs, thoracic radiotherapy and toxic exposures may trigger organising lung injury; the exposure timeline is therefore central.

Pathophysiology

  1. 1
    Alveolar epithelial injury

    A pulmonary insult damages distal airways and alveoli, prompting an exudative inflammatory response, and the downstream physiological effect determines clinical severity.

  2. 2
    Granulation tissue plugs

    Fibroblasts and connective tissue grow within alveolar ducts, alveoli and bronchioles as intraluminal buds while the underlying lung architecture remains relatively preserved.

  3. 3
    Patchy airflow and gas-exchange loss

    Affected regions become poorly ventilated, producing subacute cough, breathlessness, systemic symptoms and migratory peripheral consolidation, which helps produce the characteristic physiological impairment.

  4. 4
    Potential resolution

    Because the organising tissue is intraluminal rather than established destructive fibrosis, it may regress, although relapse or residual change can occur.

Clinical features and red flags

Migratory peripheral consolidation

Serial imaging shows patchy peripheral or peribronchovascular consolidation that appears in different sites, often with ground-glass change or perilobular linear opacities.

Secondary organising pneumonia

Recent new medicine, connective-tissue symptoms, radiotherapy field, transplantation, inflammatory disease, cancer treatment or antecedent infection provides a possible cause that changes management and naming.

Severe diffuse presentationRed flag

Rapidly spreading bilateral opacity, profound desaturation, tachypnoea or exhaustion can resemble ARDS and requires emergency respiratory and critical-care assessment.

Malignancy warningRed flag

A persistent focal mass-like consolidation, haemoptysis, unilateral nodes or weight loss out of proportion to inflammation should enter an urgent lung-cancer pathway.

Atypical non-responseRed flag

Failure to improve after an adequate supervised corticosteroid trial should prompt urgent reconsideration of infection, lymphoma, adenocarcinoma, eosinophilic pneumonia, vasculitis or an incorrect pathological label.

Investigations

  1. 01
    Chest radiograph and HRCTFirst step
    Why
    Define extent, distribution and features requiring another pathway.
    Interpretation and limitations
    Peripheral or peribronchovascular consolidation, ground glass and perilobular change support organising pneumonia. Cavitation, a fixed focal lesion, marked nodes or pleural disease broadens the differential.
  2. 02
    Full blood count, CRP, renal and liver profiles
    Why
    Assess inflammatory burden, eosinophilia, organ dysfunction and treatment safety.
    Interpretation and limitations
    Raised inflammatory markers are common but nonspecific. Marked eosinophilia redirects toward eosinophilic disease, while renal injury or anaemia may suggest systemic vasculitis or haemorrhage.
  3. 03
    Microbiology
    Why
    Exclude infection before starting systemic immunosuppression.
    Interpretation and limitations
    Use sputum, blood cultures, viral testing and opportunistic investigations according to severity and immune status. Prior antibiotics reduce yield but do not make infection impossible.
  4. 04
    Autoimmune and medicine review
    Why
    Identify a secondary driver that changes long-term management.
    Interpretation and limitations
    Target serology to clinical features and build a precise medicine timeline including oncology, antiarrhythmic and rheumatology agents. Temporal association supports but rarely proves causality.

Differential diagnosis

01

Persistent infection

Bacterial, mycobacterial and fungal infection can mimic organising consolidation; microbiology and exposure context require assessment before immunosuppression because treatment could worsen an unrecognised pathogen.

02

Lung cancer

Adenocarcinoma, lymphoma or an obstructing tumour may present as non-resolving consolidation, requiring adequate imaging and sometimes tissue.

03

Eosinophilic pneumonia

Blood or lavage eosinophilia and a compatible medicine or exposure history favour eosinophilic disease, despite similar peripheral opacities.

04

Pulmonary vasculitis

Haemoptysis, renal injury, purpura, neuropathy or destructive nodules suggest vasculitis rather than isolated organising pneumonia, and corroborating objective findings prevent an incorrect diagnostic label.

05

Pulmonary infarction

Acute pleuritic symptoms and thromboembolic risk with peripheral wedge-shaped opacity should prompt pulmonary embolism assessment, and the distinction changes the subsequent clinical pathway.

Additional chapter-specific clues

Subacute pneumonia mimic

Several weeks of cough, dyspnoea, feverishness, fatigue and weight loss persist despite appropriate antibacterial treatment, with multifocal rather than a single resolving lobar opacity.

Management

01Diagnostic work-upMove beyond non-resolving pneumoniaFirst stepSubacute multifocal consolidation persists despite appropriate initial antimicrobial care.+
  1. 1Reassess physiological stability and obtain HRCT, looking for organising distribution while identifying pleural, nodal or mass-like features that require a cancer or infection pathway.
  2. 2Review all medicines, radiotherapy, systemic inflammatory symptoms, immune status and microbiology; do not use the word cryptogenic until secondary causes have been addressed.
  3. 3Discuss at respiratory or ILD MDT whether clinicoradiological confidence is sufficient or lavage and tissue would change the decision.
  4. 4Document the working diagnosis and planned response measures, including when non-response will trigger biopsy or a renewed malignancy and infection search.
02TreatmentUse corticosteroids with an endpointClinically important organising pneumonia is sufficiently established.

Complications

01

Hypoxaemic respiratory failure

Extensive bilateral disease can cause marked shunt physiology and rapidly increasing oxygen requirements, particularly when baseline cardiopulmonary reserve is limited.

02

Relapse

Symptoms and opacities may recur during or after corticosteroid reduction, prompting reassessment for adherence, secondary causes and diagnostic alternatives.

03

Residual fibrotic change

A minority develop persistent architectural distortion and impaired gas transfer rather than complete radiological resolution, and increasing the burden of otherwise local respiratory disease.

04

Treatment toxicity

Prolonged systemic corticosteroids increase infection, osteoporosis, diabetes, adrenal suppression and psychological adverse effects, and increasing the burden of otherwise local respiratory disease.

Monitoring and follow-up

  • Review breathlessness, cough, fever, weight, activity and oxygenation early after treatment to confirm the expected clinical direction.
  • Repeat chest imaging after an appropriate interval to document clearing or migration and ensure a focal suspicious opacity has not persisted.
  • Trend spirometry and TLCO in physiologically significant disease, recognising that symptom improvement may precede complete radiographic resolution.
  • Monitor corticosteroid metabolic, bone, ocular, psychiatric and infection complications throughout the taper, with prevention measures documented.
  • At every recurrence review the original secondary-cause screen and cumulative medicine history rather than recording 'COP relapse' by default.
  • If long-term macrolide therapy is used, follow the BTS ECG, liver, hearing, microbiology and benefit-review framework.

Special situations

Cryptogenic is a conclusion

The pathological pattern becomes cryptogenic organising pneumonia only after a reasonable search for drug, infection, autoimmune, radiation, malignant and transplant associations.

Migration is a useful clue

Consolidation disappearing in one region and appearing in another is more suggestive of organising or eosinophilic pneumonia than an untreated fixed bacterial lobar process.

Response is not proof

Rapid improvement with corticosteroids supports but does not confirm COP; lymphoma, eosinophilic inflammation and some infections can also change after steroids.

Histology needs its surroundings

Organising tissue is a common reaction at the edge of infection, infarction or tumour. A small biopsy must be correlated with radiology and clinical behaviour.

Relapse need not mean catastrophe

Recurrence during taper is frequent and often responsive, but it should prompt confirmation and toxicity-aware replanning rather than automatic indefinite high-dose treatment.

Common pitfalls

  1. 01

    Calling persistent consolidation COP after one antibiotic course without HRCT, microbiology and malignancy consideration.

  2. 02

    Using the reverse-halo sign as pathognomonic and overlooking fungal infection, infarction or granulomatous disease.

  3. 03

    Starting outpatient steroids in an unstable hypoxaemic patient with an undifferentiated diffuse infiltrate.

  4. 04

    Retaining the word cryptogenic when a causative medicine, connective-tissue disease or radiation field becomes apparent.

  5. 05

    Interpreting early steroid response as final diagnostic proof and abandoning planned imaging follow-up.

  6. 06

    Escalating repeated steroid courses without measuring cumulative bone, metabolic, ocular and infection harm.

Practice

Two practice questions

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Question 1 of 2
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RespiratoryOriginal SBA

When cryptogenic is premature

A patient develops patchy migrating consolidation six weeks after starting a medicine known to cause lung injury. Biopsy shows organising pneumonia. What is the most accurate classification?

Choose one answer, then submit
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Sources and review status4 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • BTS interstitial lung disease guidelineArchived UK reference for organising pneumonia; use current MDT and local protocols for modern treatment decisions.
  • BTS long-term macrolide guidelineSpecialist safety framework; evidence in organising pneumonia remains limited.
  • NICE suspected cancer referral guidanceUrgent referral framework for suspicious persistent pulmonary findings.
  • Prednisolone summary of product characteristicsCorticosteroid contraindications, interactions and adverse-effect profile.

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateComplete draftClinical stateAwaiting reviewJurisdictionUnited Kingdom
Systemic corticosteroids are customary for significant symptomatic or physiological disease, yet evidence for the ideal dose and taper is limited. Mild cases may improve spontaneously or be observed by specialists. Relapse is frequent as prednisolone falls, but repeated recurrence should trigger a second look for a missed secondary driver, poor adherence, resistant infection or an alternative diagnosis. Long-term macrolide use has been discussed by BTS for organising pneumonia, but evidence is limited and specialist governance is essential.

Key points

  • Organising pneumonia is a tissue-repair pattern with intra-alveolar granulation tissue; cryptogenic organising pneumonia is diagnosed only when no cause is found.
  • Secondary triggers include infection, connective-tissue disease, medicines, radiotherapy, malignancy, inflammatory bowel disease and transplantation.
  • Patients often have weeks of dry cough, breathlessness, fever, malaise and weight loss that fail to resolve with routine antibiotics.
  • HRCT commonly shows patchy peripheral or peribronchovascular consolidation, ground glass and migrating opacities, but no single sign is pathognomonic.
  • The reverse-halo sign can support the pattern but also occurs in fungal infection, infarction, granulomatous disease and malignancy.
  • A brisk corticosteroid response is typical but is not retrospective proof; lymphoma, eosinophilic disease and infection can transiently improve or fluctuate.
  • Relapse during taper or after stopping treatment is common and usually prompts diagnostic and exposure review before simply increasing steroids.
  • Biopsy is unnecessary in every typical case but becomes important when imaging, clinical behaviour or treatment response is atypical.
  • Cryptogenic disease has no ongoing causal treatment beyond controlling the inflammatory process; secondary organising pneumonia requires the trigger addressed.
  • 05
    Bronchoscopy with lavage
    Why
    Sample for infection, malignant cells, eosinophilia and haemorrhage in selected cases.
    Interpretation and limitations
    A mixed inflammatory differential may be compatible but is not diagnostic. Lavage is most valuable when it changes the safety of corticosteroid treatment.
  • 06
    Transbronchial or surgical lung biopsy
    Why
    Confirm morphology when diagnosis remains uncertain and consequences are substantial.
    Interpretation and limitations
    Organising plugs must be interpreted alongside the wider specimen because they can sit adjacent to tumour, infection or another ILD. Surgical sampling carries morbidity and is not automatic.
  • 07
    Pulmonary function and exercise oxygenation
    Why
    Measure physiological severity and provide a response baseline.
    Interpretation and limitations
    Restriction and reduced TLCO are common; hypoxaemia or exertional desaturation increases urgency. Improvement should be judged with symptoms and imaging rather than spirometry alone.
    • +
    1. 1Correct hypoxaemia and address an identified trigger; complete appropriate infection assessment before immunosuppression and involve oncology or rheumatology for secondary disease.
    2. 2For significant cryptogenic disease, begin a specialist prednisolone regimen under the local ILD protocol, explaining expected early improvement and the possibility of relapse.
    3. 3Measure response through symptoms, oxygen need, inflammatory markers, physiology and interval imaging; begin a gradual taper rather than maintaining an arbitrary full dose.
    4. 4If improvement is absent or toxicity is excessive, revisit diagnosis and seek specialist advice before adding steroid-sparing or long-term macrolide treatment.
    03RelapseRecheck cause before repeating treatmentSymptoms and compatible infiltrates recur during taper or after apparent recovery.+
    1. 1Confirm objective recurrence and reassess oxygenation; distinguish relapse from bacterial or opportunistic infection, embolism, oedema and steroid withdrawal symptoms.
    2. 2Repeat the medicine, autoimmune, exposure and cancer review, paying attention to a fixed rather than migrating lesion or new systemic signs.
    3. 3AlternativeDiscuss a slower corticosteroid strategy or alternative specialist therapy according to severity and cumulative toxicity, using the minimum exposure that controls disease.
    4. 4Strengthen bone, metabolic and infection prevention, and define an urgent plan for future fever, hypoxaemia or focal symptoms.
    Key medicines and prescribing safety2 treatments · regimens, roles and cautions+
    Usual first-line anti-inflammatory treatment for symptomatic, hypoxaemic or physiologically important cryptogenic organising pneumonia.

    Prednisolone

    There is no single current UK regimen for COP; specialist practice uses a daily induction tailored to physiological severity, followed by a slow response-guided taper over months under the local ILD protocol.

    Establish reasonable diagnostic confidence and assess infection first. Monitor glucose, blood pressure, mood, weight, bone and eye health; relapse is common during taper, while lack of response should challenge the diagnosis rather than trigger endless dose escalation.

    Occasional steroid-sparing or mild-disease strategy where specialist judgement finds potential benefit despite limited evidence.

    Long-term macrolide in selected cases

    No routine COP dose should be copied across services; if an ILD specialist uses azithromycin or clarithromycin off label, follow the BTS macrolide and local antimicrobial protocol exactly.

    Exclude non-tuberculous mycobacterial infection where relevant and review ECG QTc, liver function, hearing, interactions and antimicrobial resistance. This is not a substitute for investigating a focal lesion or treating severe hypoxaemia.

    Pulmonary function, oxygenation and imaging trajectory should guide treatment duration rather than pursuing complete radiographic clearing at any toxicity cost.