Comedian Bernie Mac died on Saturday (August 9) of complications from pneumonia. In the coverage of his death, the media has reported that in 1983, doctors diagnosed him with a mysterious ailment called sarcoidosis.

His publicist says that his three-week battle with pneumonia and his sarcoidosis were unrelated, and CNN reported earlier this week that Mac said his sarcoidosis had entered remission in 2005. But it can be fatal: Sarcoidosis of the heart and lungs was implicated in the death of pro football Hall of Famer, Reggie White, in 2004.

So what is sarcoidosis?

People with the disease typically develop shortness of breath or a dry cough as inflammation cuts down on their lung capacity. The disease—which may infect up to a million people worldwide—affects ethnic groups differently. For example, in 80 to 90 percent of Caucasians who develop it, it simply disappears over time, even without treatment. Meanwhile, in African-Americans, the disease progresses more aggressively, causing more symptoms and resulting in more hospital visits and longer courses of treatment.

Scientific talked to Om Sharma, a sarcoidosis expert at the LAC+U.S.C. Medical Center, to find out more about the illness. An edited interview transcript follows.

What is sarcoidosis?
It's an inflammatory lung disease. The cause of this inflammation is not known, but it almost always affects the lungs first. Ninety percent of the patients have lung involvement, but sarcoidosis can affect any organ in the body--lungs, skin, eyes, heart, brain, bones.

Most of the sarcoidosis patients go to a doctor because of shortness of breath or dry cough or maybe their chest X-ray is found to abnormal during a routine examination. The abnormality that is caused by sarcoidosis is quite typical: an enlargement of the glands in the lungs and scar tissue in the lungs.

What are the symptoms as the disease progresses?
In the beginning, it may be shortness of breath while playing a game of tennis or something. But, later on you might get shortness of breath by just walking a few blocks. And then later you might get shortness of breath while just doing housework. The same can happen to the cough, if it is mild. So, those are symptoms of the lung disease.

If you get skin sarcoidosis, you get lesions on the skin…. They don't go away--and they may progressively get worse. If someone gets sarcoidosis of the eye, then they have blurry vision or redness of the eyes and pain in the eyes. If it's not treated, one could get even blindness or glaucoma. If sarcoidosis affects the liver, then liver function could become abnormal. So, symptoms of the disease depend on the organ involved. But, most of the patients have lung disease.

What do the skin lesions typically look like?
The skin lesions can be of two main types. The first is always on the legs. They are large, red bumps, like small strawberries. They are very sudden--the patient wakes up with them. They often say, "I was all right yesterday, then I woke up this morning and these things had appeared." These are called erythema nodosum and they always indicate that the sarcoidosis will go away--it's a good prognosis. They always occur in Caucasians. And they will go away in about six weeks and the sarcoidosis will disappear in anywhere from six months to 18 to 24 months.

African-Americans get different lesions. They are on the face. They are either little nodules or big patches. They are almost always symmetrical, so if they are on one cheek, they will be on the other one, as well. If they are on the forehead, they'll be on the whole forehead. If they are on the trunk, both sides of [the] trunk will be affected. If they are on the limbs, the limbs on both sides will be affected. So, they are reddish, blue patches. They are not tender and they are not painful, so they are not like erythema nodosum. These are the chronic sarcoidosis skin legions and when they occur, it means the disease will stay with the patient for a long time.

But, the skin lesions by themselves don't reduce life expectancy because no other organ is involved. But, many times they are treated because they look ugly.

If it spreads to other organs, is it a fatal illness?
In [fatal diseases such as emphysema or diabetes], spontaneous remission [is never] seen. Cancer, once diagnosed, never goes away. In sarcoidosis, depending on your genes, in 80 to 90 percent of people it will go away. So, it's a fairly benign disease.

In African-Americans, it progresses, so there's a mortality of 5 to 6 or 7 percent in African-American patients.

Could sarcoidosis have killed Bernie Mac?
Bernie Mac's sarcoidosis was quite extensive. I understand he had lung disease and skin involvement. Then he was admitted to a hospital in Chicago somewhere where he developed pneumonia.

His sarcoidosis, I think, was stable; that means it was brought under control by medicine he was taking because he has been able to work. So, I have a feeling it was not causing too many problems.

The treatment which he might have been getting might have caused a depression of immunity and may have made him catch these infections that might have caused pneumonia that may have been the cause of his death. I don't know, because he was in Chicago and I am in Los Angeles.

What are the treatments for sarcoidosis?
Since we don't know the cause of sarcoidosis, there is no specific treatment. You have a treatment for, say, tuberculosis because we know that bacteria causes tuberculosis and we have a half a dozen antibiotics that kill the tuberculosis bug.

Most sarcoidosis patients receive corticosteroids, like prednisone, or steroids. Some patients receive other drugs called immunosuppressive drugs. And the function of all these drugs is similar: They suppress the inflammation. They suppress granuloma formation and prevent the granuloma from developing into scar tissue.

Not all the patients respond to treatment. Some patients take prednisone and steroids for years--20, 30 years--and their disease remains under control, but it never goes away. When you stop the medicine, it comes back. This happens most often in African-American patients—depending on one's genes it manifests either in a relatively harmless way or in a progressive, dangerous manner.

If one's genes can determine how the illness progresses, are there genes that predispose a person to developing sarcoidosis?
It's not like cystic fibrosis. We know exactly what gene is involved in cystic fibrosis. In sarcoidosis, there isn't one gene. There are what we call "polymorphism of many genes"--so, it's complicated.

There's no single genetic component involved in getting it in the first place. But, certain races have a bad prognosis. So, I think anybody can get sarcoidosis and it is caused by something that comes from the outside because it appears in the lungs first--so, it must be inhaled.

Because it occurs everywhere--here, in Japan, in South Africa, Australia--it can't be related to the geography of the patient or the occupation of the patient. It is not related to any inhalation of any dust or chemicals or molds. It usually affects young people between the ages of 20 and 45 or 50. There is a second peak a little later, at the age of 55 or 60, in women. Almost all [patients] are healthy before they develop sarcoidosis, so there is no predisposing illness that makes the individual prone.

What does the site of a sarcoidosis inflammation look like? What cells are involved?
If the glands are enlarged in the lungs, we take biopsy from those glands. And those glands will show what we call granulomas--which are nothing but collections of inflammatory cells that include the lymphocytes and the giant cells and macrophages.

They are probably there to get rid of something that has invited them [to that site]. We don't know what that something is, so we don't know the exact cause of sarcoidosis.