A Common Fungus Fosters a Rare Disease: Fibrosing Mediastinitis

A Common Fungus Fosters a Rare Disease: Fibrosing Mediastinitis
Fibrosing mediastinitis is an often missed diagnosis.

In much of the U.S., histoplasmosis, a fungal infection that causes nearly all of the nation’s cases of fibrosing mediastinitis (FM), seldom occurs; clinicians in those areas often lack familiarity with FM, and affected patients frequently go undiagnosed or misdiagnosed. Patients are also often subjected to unnecessary, invasive testing, when a CT scan is often the only test needed.

Vanderbilt University Medical Center resides in the midst of the U.S. region where histoplasmosis is endemic, and the Vanderbilt Lung Institute focuses heavily on this rare illness.

“Our team probably has the deepest experience of fibrosing mediastinitis in the nation and the world,” said Justin Hewlett, M.D., an assistant professor of medicine in the Division of Allergy, Pulmonology and Critical Care Medicine at Vanderbilt. “We have managed the care of over 450 patients with the disease. That is a large number.”

Bats and Birds to Blame

The endemic area for histoplasmosis centers upon the Mississippi and Ohio River Valleys. In the U.S., the vast majority of FM cases are caused by histoplasmosis infections resulting from a person’s exposure to the fungus in the droppings of bats and birds, which wind up in soil.

According to the National Organization of Rare Diseases (NORD), far fewer than 1 percent of the people who develop histoplasmosis will also have the overblown healing response to that infection that can lead to FM. Although reliable prevalence data is not available for FM, NORD states that the population affected by the disease in the U.S. is several hundred people.

Histoplasmosis infections are common, but almost always follows a benign course, Hewett explained. Uncommon causes of FM in the U.S. include radiation therapy, autoimmune disease and tuberculosis.

“FM is commonly labelled as sarcoidosis or chronic granulomatous lung disease, but sarcoidosis treatments don’t work for FM.”

When FM does occur, its main features include the buildup of excess collagen, fibrosis tissues, and inflammatory cells in the mediastinum, which can eventually block airways or blood vessels that enter and leave the lungs. The disease typically develops decades after an exposure, Hewlett said.

Consulting with Clinicians in Less Affected Areas

In a mobile society, people from FM endemic regions fan out widely, and later develop symptoms. “We provide consultative services to clinicians all over, calling from states where they don’t get histoplasmosis complications often,” Hewlett said. Erroneous diagnoses and unneeded interventions occur frequently, he added.

“A patient at another institution will have a CT scan that shows scarring in the mediastinum. They’ll often undergo a series of biopsies and other tests seeking the cause.” In fact, FM can usually be diagnosed on the basis of a CT scan alone; further tests are not generally needed and are often unrevealing, Hewlett says.

Despite imaging, some patients may still not receive a diagnosis, and be left hanging. They are often misdiagnosed, too. “FM is commonly labelled as sarcoidosis or chronic granulomatous lung disease, but sarcoidosis treatments don’t work for FM,” Hewlett said.

FM is one of several lung diseases often subject to misidentification and mistreatment.

Most FM Patients Do Well

“Eighty percent of FM patients have one-sided disease, affecting only one lung; for them, quality of life is usually quite good,” said Hewlett, adding that there is no evidence that, for this group, life expectancy is decreased.

For the other 20 percent, with two-sided disease, the condition can be life-shortening, Hewlett explained, adding that common complications include coughing up blood and recurrent pneumonias. “These issues can be managed with stenting, embolization, and some inhaled medications; also, antibiotics as needed for the pneumonias,” he said.

“The Internet paints a terrible picture — that FM progresses and that nothing can be done, which is not true.”

Most FM interventions are not surgeries but procedures such as stenting an airway or a blood vessel. Furthermore, most FM patients do not require intervention, Hewlett explained.

“The Internet paints a terrible picture — that FM progresses and that nothing can be done, which is not true,” Hewlett said. He explained that his initial conversations with an FM patient usually focus on educating them, providing guidance on symptoms to watch for and report, and helping them manage expectations.