Pathology
Pulmonary fibrosis, scarring in the lungs

Rare Fibrotic Diseases



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Pulmonary fibrosis, scarring in the lungs
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"Rare Fibrotic Diseases"
Caption: Pulmonary fibrosis, scarring in the lungs
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Fibroinflammatory disorders are relatively new designations for rare heterogeneous disease states in which inflammation causes tissue damage and scarring, known as fibrosis. Idiopathic fibroinflammatory disorders have no known cause or mechanism, and those with known causes are secondary to these idiopathic processes. Meaning that the ultimate cause of these disorders is not currently understood. Making diagnosis and prevention even more difficult is the mistaken identity many of these disorders take on, presenting as other diseases. The one theory that seems most prevalent is the potential autoimmune basis for these disorders that have been described in nearly every organ.

Pseudotumors

A 1998 paper by Dehner and Coffin in Seminars in Diagnostic Pathology referred to these conditions as fibrosclerotic, and they described conditions that tend to occur in the same person in different organs, but with the same fibrotic etiology. Called pseudotumors, or nonneoplastic fibroinflammatory tumors, these masses compress various structures within the organ and displace the anatomic boundaries of the tissue. The suspected mechanism at that time, and accepted now, was inflammation.

In their paper, known primary pseudotumors included Riedel thyroiditis, a rare chronic inflammation of the thyroid that results in fibrotic tissue replacing the gland; retroperitoneal fibrosis, a condition in which the ureters between the kidneys and bladder are blocked; sclerosing mediastinitis, a buildup of fibrotic tissue in the chest due to chronic inflammation; sclerosing cholangitis, a form of chronic liver disease; and orbital pseudotumor, a swelling of the eye . Also mentioned were malignant fibroinflammatory tumors, known as inflammatory myofibroblastic tumors, which, though rare, have been noted to occur in many organs, especially the lungs.

Another form of fibroinflammatory disorder not mentioned by these researchers is sclerosing mesenteritis. This fibrotic lesion occurs in the lining of the small intestine. It may mimic more aggressive cancers, but is itself generally benign according to a 2007 case report.

Secondary fibroinflammatory disorders

In addition to pseudotumors, Dehner and Coffin named other fibroinflammatory disorders, as they might be related to the mechanism underlying their focus. Secondary fibroinflammatory processes include inflammatory polyps in the gastrointestinal tract; sclerosing peritonitis, which is thought to be a widespread version of retroperitoneal fibrosis;  focal myositis, a pseudotumor of the skeletal system, and calcifying fibrous pseudotumor, which is thought to be the late stage of inflammatory myofibroblastic tumor.

Tumefactive inflammatory lesions

Many of the pseudotumors can also be classified as tumefactive inflammatory lesions. Tumefaction is the process of swelling. This type of lesion has been described in the various glands of the head and neck region, with 20 percent of cases presenting with similar lesions in other parts of the body according to a textbook on Diagnostic Surgical Pathology of the Head and Neck published by Elsevier and Saunders in 2009. At that time, they noted only 30 known cases with such lesions.

Chronic periaortitis

One particular form of fibroinflammatory disease that has drawn interest is chronic periaortitis. Once thought to be secondary to atherosclerosis, this disorder has gained attention due to potential autoimmune mechanisms triggering the buildup of fibrosis around the abdominal aorta. The condition is diagnosed by imaging and treated with anti-inflammatories and surgery.

Possible pathogenesis

As mentioned already, autoimmune mechanisms are thought to play a role in these disorders. It is also clear that the presence of one type of pseudotumor often means the presence of multiple pseudotumors throughout the body. What is truly primary and secondary has yet to be fully sorted out. However, an example of this process is the work done on retroperitoneal fibrosis. It appears to be the manifestation of IgG4-related sclerosing disease, which was first characterized in 2006 and is most commonly seen as autoimmune pancreatitis. In fact, this reaction to increased levels of IgG4 (hyper-IgG4 disease) is now thought to be the common mechanism underlying these diseases.

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