LabMed

Lymphoid Interstitial Pneumonia (LIP)

At a Glance

Lymphoid interstitial pneumonia (LIP) is characterized by dyspnea, cough, and fever accompanied by bibasilar interstitial pulmonary infiltrates. Lymphoid interstitial pneumonia is uncommon but occurs worldwide in both children and adults. The overwhelming majority of LIP patients have an associated autoimmune/collagen vascular disease, lymphoma, chronic viral infection, or graft-versus-host disease (GVHD) following allogeneic bone marrow or hematapoietic stem cell transplant. The most common associated viral infections are human immunodeficiency virus (HIV) type 1, Epstein-Barr virus, and human T-cell leukemia virus (HTLV) type 1 (especially in patients from the Caribbean, Africa, and southwestern Japan). Pediatric LIP patients are more prone than adults to develop lymphadenopathy and hepatosplenomegaly.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

No laboratory tests can confirm a specific diagnosis of LIP. Clinical setting, a chest radiograph that reveals interstitial infiltrates, and either transbronchial biopsies or an open wedge lung biopsy that reveals lymphoid infiltrates are critical to diagnosis. Laboratory testing that supports an "associated disease" diagnosis (e.g., autoimmune serology, viral serology, and either specific antigen or nucleic acid studies) is contributory. Some patients exhibit nonspecific laboratory findings, such as polyclonal hypergammaglobulinemia and/or elevated lactate dehydrogenase concentrations. In addition to dense interstitial infiltrates of small, mature lymphocytes, lung tissue may contain plasma cells, occasionally small noncaseating granulomas, and interstitial fibrosis. In some cases, lymphocytes are also found within alveolar spaces.

HIV-1-infected patients who possess HLA-DR5 or HLA-DR6 alleles are predisposed to LIP. Lymphocytic interstitial pneumonia is relatively frequent (22-75%) in children with HIV-1 infection and lung disease. A much lower proportion of HIV-1-infected adults suffer from LIP. In addition, a variety of cytokines, including IL-2, IL-18, IL-12, MIP-1 alpha, MIP-1 beta, and RANTES, are found in high concentrations in affected lung tissue. Again, none of these findings are diagnostically specific.

The most important follow-up tests in LIP patients are studies to rule out infectious complications and, in rare patients, malignant lymphoma.

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications - OTC drugs or Herbals - that might affect the lab results?

The chief issue relevant to laboratory testing in patients suspected of having LIP is that this entity occurs in the setting of many different diseases (e.g., autoimmune, inflammatory, lymphoproliferative, GVHD, chronic viral infection) and yet is not characterized by specific laboratory abnormalities.

What Lab Results Are Absolutely Confirmatory?

There are no absolutely confirmatory laboratory test results. Diagnosis of LIP is made based on clinical setting, clinical manifestations, and lung biopsy.

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications - OTC drugs or Herbals - that might affect the lab results?

Nearly all of the disorders that constitute a setting in which LIP may occur also predispose affected patients to infections that may be difficult to distinguish. Careful diagnostic testing for easily confused infectious diseases is very important. Failure to consider infectious diseases that may mimic LIP can lead to misdiagnosis.

Additional Issues

Lymphoid interstitial pneumonia is seen in a wide variety of clinical settings, varies in severity, and can vary somewhat between pediatric and adult patients. Clinical suspicion is paramount.

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