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Pneumonia, Interstitial

Synonyms of Pneumonia, Interstitial

  • Bronchiolitis Obliterans Organizing Pneumonia (Boop)
  • Chronic Fibrous Pneumonia
  • Diffuse Alveolar Damage
  • Fibrous Interstitial Pneumonia
  • Giant Cell Interstitial Pneumonia
  • Idiopathic Interstitial Pneumonia
  • Usual Interstitial Pneumonia (UIP)

Disorder Subdivisions

  • Acute Interstitial Pneumonia (AIP)
  • Cryptogenic Organizing Pneumonia (COP)
  • Desquamative Interstitial Pneumonia (DIP)
  • Idiopathic Pulmonary Fibrosis (IPF)
  • Lymphoid Interstitial Pneumonia (LIP)
  • Nonspecific Interstitial Pneumonia (NSIP)
  • Respiratory Bronchiolitis-Associated Interstitial Lung Disease (RB-ILD)

General Discussion

The abnormal accumulation of inflammatory cells in lung tissue may lead to any one of several disorders with similar signs and symptoms. As white blood cells and protein-rich plasma build up in the air sacs of the lungs (alveoli), inflammation is generated. The inflammatory process, if it lasts long enough, may harden the fluid and the resultant firm, fibrous substance (scarring) may replace the lung tissue. If the scarring is extensive, the air sacs may be destroyed over time and the resultant space replaced by cysts.

The American Thoracic Society and the European Respiratory Society jointly studied the interstitial pneumonias during 2001 and issued a Multidisciplinary Consensus Classification of the Idiopathic Interstitial Pneumonias. This consensus statement was intended to replace several older classification schemes that had led to a confusion of names and syndromes.

Participants agreed that the Idiopathic Interstitial Pneumonias (IIPs) comprise a number of clinical entities that are each rare and sufficiently different from one another to be considered as distinct disorders. This report follows the joint ARS/ERS classification.


Symptoms of Interstitial Pneumonia may vary from mild to severe according to the extent of lung involvement, accumulation of tissue and cells not normally found in the lungs (infiltrate), the rate of progress, and the presence of complications (such as other lung infections). The patient often has no fever (afebrile). Occasionally, however, the onset may be rapid, with fever, suggesting an acute respiratory infection. Symptoms of lung disease may be few, except for shortness of breath on exertion (exertional dyspnea). Cough is not normally a prominent feature nor is overproduction of mucous; these symptoms are more likely to be present when there is a secondary airway (bronchial) infection. Blue coloring of the skin, fingernails and around the lips (cyanosis) may occur, signaling a low level of oxygen in the blood. Loss of appetite (anorexia), weight loss, fatigue, weakness, and vague chest pains may also be present.

Idiopathic Pulmonary Fibrosis (IPF)
Symptoms appear gradually over time and include considerable difficulty in breathing (dyspnea), in some cases to the point of disablement. The common age of onset is about 50 years with more males than females affected. The blood levels of a particular type of white blood cell may increase beyond the normal range. IPF is a distinctive type of long-standing (chronic), interstitial pneumonia that, upon surgical lung biopsy, shows a very particular, identifiable pattern of cell organization (histological) known as Usual Interstitial Pneumonia (UIP).

Nonspecific Interstitial Pneumonia (NSIP)
Some lung biopsies performed on patients with IP do not show cell patterns (histological patterns) that conform to expectations, so that a place for unclassified IP had to be created. This idea has helped to identify a group of lung disorders that have a more favorable prognosis. The puzzle remains regarding the identification of NSIP since there is no recognized and distinctive clinical description for patients with this histologic pattern on lung biopsy. Most cases appear when patients are in their 40s and 50s, although some cases involving children have been reported. Breathlessness, cough, and fatigue are the usual symptoms.

Cryptogenic Organizing Pneumonia (COP)
Although this was known for some time as bronchiolitis obliterans organizing pneumonia (BOOP), the ATC/ERS prefer the term Cryptogenic Organizing Pneumonia (COP) because it better describes the syndrome and avoids confusion with other thoracic diseases with similar names. A patient who presents with a peculiar, distinct organization of the cells of the air sacs (alveoli) and the air ducts (alveolar ducts) is said to present with organizing pneumonia. Thus, patients may present with organizing pneumonia associated with rheumatoid arthritis or organizing pneumonia secondary to viral pneumonia. The term cryptogenic is used to emphasize that the associated cause has to be unmasked. Clinical onset is usually around age 55, and patients usually present with a history of a short period of coughs and breathlessness. Recovery is usually complete with the possibility of relapse.

Acute Interstitial Pneumonia (AIP)
AIP progresses rapidly and is distinguished by the particular nature or pattern of cells found on biopsy of the lung. This pattern is almost identical to that found with Acute Respiratory Distress Syndrome and may be confused with it. The name and its abbreviation, AIP, are limited to those cases of unknown cause.

Respiratory Bronchiolitis-Associated Interstitial Lung Disease (RB-ILD)
RB-ILD is defined as the presentation of interstitial lung disease characterized by diseased lesions of inflamed bronchial tubes (bronchiolitis). It is almost invariably associated with smoking. The disorder is related, in some complex and little understood way, to Desquamative Interstitial Pneumonia (see below) and is generally benign. RB-ILD rarely presents symptomatically, but in rare instances significant breathing difficulties may be associated with abnormal radiological findings.

Desquamative Interstitial Pneumonia (DIP)
DIP is misnamed, but because of the rarity of this disorder, the members of the Consensus Committee decided to keep it. It is now understood that what, on histological examination, were thought to be cells from the lining of the affected bronchial air passages are really intra-alveolar macrophage accumulation. This term simply means that there is an accumulation of a particular type of large, infection-fighting, white blood cells (macrophages) in the spaces between the air-sacs (intra-alveolar). DIP is usually noticed in the fourth and fifth decades, and is more common among men because they are more often smokers. Breathlessness and a dry cough may be present for months and, in rare cases, may lead to respiratory failure or collapse.

Lymphoid Interstitial Pneumonia (LIP)
LIP is an uncommon form of interstitial pneumonia characterized by the presence of cells from the lymph system through the spaces between the lung tissue. It is important to remember that this disorder is not, as was once thought, a precursor of lung cancer. Gradually, a dry cough and breathlessness (dyspnea) will get worse over three or more years. Patients usually are diagnosed in their fifth decade, and LIP is more common in women than in men. Some authorities believe LIP to be an autoimmune disorder.


The causes of the different interstitial pneumonias are not well understood. Each type can be precisely diagnosed by the study of the lung tissue (histology). Unlike many other types of pneumonia, the IIPs are not usually caused by bacteria. Some are clearly linked to smoking and others are associated with working or exposure to heavy metals. Some cases of COP are linked to viruses or bacteria.

Affected Populations

Interstitial Pneumonia affects slightly more men than women. It has generally been reported within an age range between 12 and 63 years. A study limited to New Mexico found the prevalence of interstitial pneumonia to be about 81 per 100,000 males and 67 per 100,000 females. The IIPs are rare in children but increase with advancing age.

Related Disorders

Symptoms of the following disorders can be similar to those of Interstitial Pneumonia. Comparisons may be useful for a differential diagnosis:

Fibrosing Alveolitis is an inflammatory lung disorder characterized by abnormal formation of fibrous tissue between the alveoli or ducts in the lungs. Coughing and cyanosis may occur. (For more information on this disorder, choose "Alveolitis, Fibrosing" as your search term in the Rare Disease Database.)

Extrinsic Allergic Alveolitis is a lung disorder resulting from repeated inhalation of organic dust, usually in a work setting. (For more information on this disorder, choose "Alveolitis, Extrinsic Allergic" as your search term in the Rare Disease Database.)

Idiopathic Pulmonary Fibrosis is an inflammatory disease of the lung tissue characterized by cellular infiltration, an interstitial thickening, and may involve the alveoli, blood vessels, airways (bronchi) and membranes surrounding the lungs (pleura). The cause is unknown.

Standard Therapies

Treatment of Interstitial Pneumonia is usually with corticosteroid drugs in patients who have no evidence of extensive fibrosis. Oxygen may be prescribed in cases of lack of oxygen levels in the blood (hypoxemia). Antibiotics are required if secondary bacterial infection occurs. Other treatment is symptomatic and supportive.

Investigational Therapies

Information on current clinical trials is posted on the Internet at All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.

For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222
TTY: (866) 411-1010

For information about clinical trials sponsored by private sources, contact:

Organizations related to Pneumonia, Interstitial


American Thoracic Society/European Respiratory Society International Multidisciplinary Consensus Classification of the Idiopathic Interstitial Pneumonias. Am J Respir Crit Care Med. 2002;165:277-304.

Crystal RG, Bitterman PB, Mossman B, et al. Future research directions in idiopathic pulmonary fibrosis: summary of a National Heart, Lung, and Blood Institute working group. Am J Respir Crit Care Med. 2002;166:236-46.

Kuwano K, Hagimoto N, Hara N. Molecular mechanisms of pulmonary fibrosis and current treatment. Curr Mol Med. 2001;1:551-73.

Demedts M, Wells AU, Anto JM, et al. Interstitial lung diseases: an epidemiological overview. Eur J Respir Suppl. 2001;32:2s-16s.

Verleden GM, du Bois RM, Bouros D, et al. Genetic predisposition and pathogenetic mechanisms of interstitial lung diseases of unknown origin. Eur J Respir Suppl. 2001;32:17s-29s.

Taylor DA, du Bois RM. Idiopathic interstitial pneumonias: a reappraisal of idiopathic pulmonary fibrosis. Int J Tuberc Lung Dis. 2001;5:1086-98.

Nicholson AG, Fulford LG, Colby TV, et al. The relationship between individual histologic features and disease progression in idiopathic pulmonary fibrosis. Am J Respir Crit Care Med. 2002;166:173-77.

Brack T, Jubran A, Tobin MJ. Dyspnea and decreased variability of breathing in patients with restrictive lung disease. Am J Respir Crit Care Med. 2002;165:1260-64.

Bouros D, Hatzakis K, Labrakis H, et al. Association of malignancy with diseases causing institial pulmonary changes. Chest. 2002;121:1278-89.

Qureshi RA, Ahmed TA, Grayson AD, et al. Does lung biopsy help with interstitial lung disease? Eur J Cardiothorac Surg. 2002;21:621-26.

Altschuler EL. Consideration of mycophenolate mofetil for idiopathic pulmonary fibrosis. Med Hypotheses. 2001;57:701-02.

Shaw RJ, Djukanovic R, Tashkin DP, et al. The role of small airways in lung disease. Respir Med. 2002;96:67-80.

Du Bois RM, Wells AU. Cryptogenic fibrosing alveolitis/idiopathic pulmonary fibrosis. Eur Respir J Suppl. 2001;32:43s-55s.

Kuhn JP, Brody AS. High-resolution CT of pediatric lung disease. Radiol Clin North Am. 2002;40:89-110.

The Merck Manual. Acute Interstitial Pneumonia. In: Idiopathic Interstitial Lung Diseases. Sec. 6, Ch 78. 2pp.

Duke University School of Medicine. What is Pulmonary Fibrosis? nd. 4pp.

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Report last updated: 2008/03/22 00:00:00 GMT+0

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