She had this chest cold she couldn't seem to shake. Days turned into weeks, and yet it lingered. Over-the-counter medicine wasn't helping.

Friends told Rancho Cordova resident Denise Peña, 37, that, hey, feeling tired and nursing a weeks-long cold was a consequence of rearing two active young children born 22 months apart.

Sick of being sick, Peña finally went to her doctor in January. Diagnosis: Bronchitis. She was given antibiotics. A few weeks later, still sick, the doctor gave her a chest X-ray. Diagnosis: Pneumonia. She was given stronger antibiotics. Weeks afterward, she went to another doctor and had another chest X-ray.

"Then I got the phone call that said there was a spot on my lungs," Peña says. "I immediately thought the worst – cancer. The doctor wanted to do a CT scan on the day of my daughter's birthday party.

"At that point, I thought I was dying and didn't want to miss the party. I took the test a few days later."

And, at last, Peña was given a definitive diagnosis: sarcoidosis.

"They tried to explain it to my husband and I," she says, "but it's hard to understand at first."

They quickly learned that this immune-system disorder causes tiny lumps of cells to cluster in the body's organs. There is no cure, and researchers have yet to identify its causes. Often, the condition goes into remission and occasionally goes away with use of the steroid prednisone.

In some cases, sarcoidosis has led to complications – stroke, organ failure – and death.

This little-known disorder was thrust into the spotlight earlier this month when comedian Bernie Mac died of pneumonia at age 50. Though Mac's publicist says his sarcoidosis was in remission, pneumonia is said to be prevalent among patients.

"It affects mostly the lungs, but sarc is called the Great Mimicker," says Dr. Amit Karmakar, a pulmonologist at Mercy San Juan Medical Center. "Sometimes, people don't even know they have it because they are asymptomatic. Or they'll have some nonspecific complaints like fatigue or muscle aches."

In Peña's case, it was fatigue and chest tightness. But her CT scan showed that the sarcoidosis had settled in her lungs, spleen and liver. After three months of taking prednisone, Peña says she feels much better.

What she doesn't like are the side effects from the steroid – weight gain and acne, in her case – but she notices the fatigue and chest tightness return when her dosage goes down.

Her husband, Isaias, who is a jujitsu instructor, has encouraged her to exercise, but Peña says she has learned to conserve her energy for her children, son Nichos, 7, and daughter Arissa, 5.

"The thing that's bad about this disease is that people can't see it because it's internal," she says. "You look fine on the outside, and they expect you to keep going like you would normally if you weren't sick. You can't. They say, 'Why are you sitting there? Why don't you get up and do something?' "

When smoke blanketed the Valley during the recent fires, Peña says, she had to stay indoors. Mostly, she doesn't let the condition stop her from playing with the kids.

There is a trade-off.

"Last week, I took my children to Marine World, and it took two days to recover from that outing," she says. "The walking uphill and on stairs was taxing on the lungs. But you just have to get up and do it because you still have a family to raise."

Peña has plans to return to the work force this fall, when both children will be in school a full day. She's concerned how she'll hold up but remains optimistic.

"I try to talk myself up," she says. "There are times when you get depressed, but you can't let life go by."

Call The Bee's Sam McManis, (916) 321-1145.