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Organising pneumonia (OP) is a relatively rare interstitial lung disease. It´s definition is based on a characteristic histological pattern in the presence of certain clinical and radiological features. Organising pneumonia represents also what has been called Bronchiolitis Obliterans Organising Pneumonia (BOOP). Recently it has been recommended to call OP cryptogenic organising pneumonia (COP) when no definite cause or characteristic clinical context is found and secondary organising pneumonia (SOP) when causes can be identified such as infection or it occurs in a characteristic clinical context such as connective tissue disorder. The most common clinical symptoms are dyspnea, cough, fever and general malaise. It is common that symptoms have been present for some weeks before the diagnosis is made. Patients commonly have lowered PO2 and a mildly restrictive spirometry. Radiographic features are most often patchy bilateral airspace opacities but an interstitial pattern or focal opacities can also be seen. Most of patients respond well to steroids but relapses are quite common. The aim of this paper is to present an overview of the disease and the main results from studies on OP in Iceland. The mean annual incidence for OP in Iceland was 1.97/100,000 inhabitants. Annual incidence for COP was 1.10/100,000 and 0.87/100,000 for SOP. This is higher than in most other studies. In Iceland patients with OP had a higher standardized mortality ratio than the general population despite good clinical responses. No clinical symptoms could separate between SOP and COP.

Correspondence: Gunnar Gudmundsson, ggudmund@landspitali.is

Table I. Classification of organising pneumonia

Cryptogenic organising pneumonia	Previously called bronchiolitis obliterans organising pneumonia (BOOP)
Organising pneumonia of a known cause
Bacteriae	Example: Clamydia pneumoniae, Legionella pneumophilia, Mycoplasma pneumoniae, Streptococcus pneumoniae and Staphylococcus aureus.
Viruses	Example: HIV, Influenza virus, Herpes virus, Cytomegalovirus and parainfluenza virus.
Fungi	Example: Cryptococcus neoformans.
Parasites	Example: Plasmodium vivax.
Drugs	Example: amiodarone, nitrofurantoin, busulfan, bleomycin, amphoterecin B, karbamazepin, methotrexate, fenytoin, sotalol, sulfasalazine and tacrolimus.
Irradiation	Most commonly in connection with breast cancer.
Organising pneumonia within a specific context
Connective tissue disorders	Rheumatoid arthritis, Sjögren´s syndrome, inflammatory myopathies and Polymyalgia rheumatica.
Vasculitides	Wegener’s vasculitis and Polyarteritis nodosa.
Transplantation	Lung and bone marrow.
Gastrointestinal disorders	Ulceritis colitis and Crohn´s disease.
Hematological disorders	Leukemia, myelodysplastic syndrome.
Lung diseases	Middle lobe syndrome, aspiration pneumonia, bronchiectasis and pulmonary infarction.

Figure I. Early stage organising pneumonia. The lung architecture is preserved. A polypoid structure (yellow arrow) of loose myxoid fibroconnective tissue with scattered fibroblasts (black arrow) is seen within a respiratory bronchiole. Also noted are reactive type 2 pneumocytes (green arrow) and mild chronic interstitial inflammation (red arrows).

 

Figure II. Later stage organising pneumonia with granulation tissue (red arrow), increased number of fibroblasts (black arrows) and newly formed blood vessels (blue arrows).

 

Figure III. Geographic distribution for organising pneumonia in Iceland.

 

Figure IV. Typical cryptogenic organising pneumonia showing patchy bilateral alveolar opacities on a) chest radiograph and b) high-resolution computed tomography scan. Published with permission from The European Respiratory Journal (12).

 

Figure V. High-resolution computed tomography showing typical cryptogenic organising pneumonia with consolidation in the left-upper lobe with an air bronchogram. Published with permission from The European Respiratory Journal (12).

 

Figure VI. High-resolution computed tomography of cryptogenic organising pneumonia presenting as solitary opacity. Published with permission from The European Respiratory Journal (12).

 

 

Figure VII. Kaplan-Meier curve of observed and expected survival in 104 patients with organising pneumonia in Iceland.