Cryptogenic Organising Pneumonia
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Direct answer
Cryptogenic organising pneumonia is an idiopathic interstitial lung disease in which patchy, migratory consolidation responds to corticosteroids and not to antibiotics. The CT often shows a reversed halo sign, a central ground-glass area surrounded by a ring of consolidation. Biopsy shows intraluminal plugs of granulation tissue in bronchioles and alveolar ducts. Corticosteroids are the mainstay of treatment, and relapse on tapering is common.
What you must remember
- Former name: bronchiolitis obliterans organising pneumonia, now called cryptogenic organising pneumonia when no underlying cause is found.
- Clinical picture: a subacute illness over weeks, with cough, breathlessness, low-grade fever, malaise and weight loss.
- Radiology: patchy, bilateral, peripheral or subpleural consolidation that shifts from one area to another on serial films.
- Histology: intraluminal granulation tissue plugs, called Masson bodies, in bronchioles, alveolar ducts and alveoli, with preserved alveolar walls.
- Secondary causes: connective tissue disease, drugs such as amiodarone and methotrexate, infection and haematological malignancy must be excluded first.
- Treatment: oral corticosteroids give a good response, but relapse on tapering is common, so a slow taper or a steroid-sparing agent is needed.
Where the exam tests pattern recognition
The exam tests whether you recognise the pattern and whether you can avoid mislabelling it.
- Trap: treating the reversed halo as diagnostic on its own Correct: it is typical of organising pneumonia but also appears in other conditions, so biopsy and clinical context are still needed.
- Trap: assuming a migrating infiltrate will clear with another antibiotic course Correct: repeated antibiotic failure in a subacute illness should raise suspicion of organising pneumonia.
- Trap: calling the disease fibrotic like usual interstitial pneumonia Correct: the lesion is intra-alveolar granulation tissue, which is generally steroid-responsive and often reversible.
- Trap: stopping steroids as soon as the film clears Correct: the taper must be slow, because relapse is common.
Frequently asked questions
What is the reverse halo sign in organising pneumonia?
The reverse halo sign is a central area of ground-glass attenuation surrounded by a ring of consolidation on CT. In cryptogenic organising pneumonia it is a characteristic pattern, but it can also be seen in other conditions, so it supports rather than proves the diagnosis.
Which histological features confirm cryptogenic organising pneumonia?
Biopsy shows intraluminal plugs of granulation tissue, often called Masson bodies, within bronchioles, alveolar ducts and alveoli. The alveolar walls are generally preserved, which helps distinguish organising pneumonia from usual interstitial pneumonia.
How is cryptogenic organising pneumonia treated?
Oral corticosteroids are the mainstay of treatment, and most patients improve within weeks of starting them. Because relapse on tapering is common, the dose is reduced slowly, and a steroid-sparing agent is added if relapses recur.
Which conditions must be excluded before diagnosing cryptogenic organising pneumonia?
Connective tissue disease, drug toxicity, infection and haematological malignancy must be excluded before the disease is labelled cryptogenic. Amiodarone and methotrexate are classic drug causes, so a detailed medication history is essential.