By Jacque Wilson and Deborah Brunswick

www.cnn.com 

It was just another day with another massive allergic reaction. 

She can always tell when one is coming on. "I just get this overwhelming sense of -- they call it impending doom." Her labradoodle, Moose, starts alerting, licking her hands frantically.

"I'll feel like I'm being stabbed in the stomach, and then it gets hard to breathe and my throat and tongue start swelling. And we have to treat it really fast." 

On that particular day in March, multiple EpiPens didn't slow the reaction. The paramedics who arrived to take Brynn to Greenville Memorial Hospital, or "Hotel Greenville" as she likes to call it, knew her well. When she asked for her security blanket, they knew to hand her her smartphone.

"New day, new crisis," Brynn quips as she tells the story, as if it's about her first day of college or a shopping trip gone wrong. It might as well be. When you're allergic to life, a near-death experience is no big deal. 

Center of attention

Less than a week after her trip to the hospital, Brynn, 21, is back at home in Easley, South Carolina. She lies on her back, her head near the foot of her bed, chattering away as her mom changes the access to her chest port. 

Melissa Duncan, a paralegal by day, dons a mask and surgical gloves before disinfecting the area around the tube that's connected to Brynn's jugular vein. The disinfectant burns, and Brynn's blood pressure hits 150/102. Her heart rate rockets to 128. 

"The meds we have to give her to keep her alive, she reacts to," Melissa says, shaking her head. "Never in a million years did I think I would be doing this. "

Brynn was seemingly a normal kid -- until she wasn't. Yes, she was a fussy baby. Yes, she got sick often as a child, Melissa muses out loud -- but what kid doesn't? Brynn was also incredibly energetic, always the center of attention. Her father, Barry, jokingly rues the day she learned to talk. She started taekwondo at the age of 9 and had her black belt by the time she was 11. That was the same year doctors diagnosed Brynn with IBS, or irritable bowel syndrome. 

"She's always been --" Melissa Duncan pauses. 

"High maintenance!" Brynn fills in with a laugh. 

It wasn't until shortly before her 16th birthday in 2010 that Brynn had her first serious allergic reaction. The next two years became a blur of sick days and doctors' appointments.

Brynn saw specialist after specialist. The gastrointestinologist diagnosed her with gastroparesis, or partial paralysis of the stomach muscles. A cardiologist said she had POTS, or Postural Orthostatic Tachycardia Syndrome -- meaning that when she stood up for longer than a few minutes, her blood pressure dropped, leaving her light-headed and nauseated. A Wake Forest doctor diagnosed her with Ehlers-Danlos syndrome, a connective tissue disorder that causes fragile skin and overly flexible joints. 

After doing hours of research, Melissa, Barry and Brynn came up with their own diagnosis: mast cell disease. They found a specialist online, Dr. Lawrence Afrin, who at the time was working in Charleston. They waited nearly nine months to see him, but hearing him confirm their suspicions was life-changing.

Mast cells are the regulators of your immune system. They're the ones that release histamine when a bug bites, or when you come into contact with an allergen. They basically sound the alarm that lets the rest of your immune system know something is wrong.

Until recently, the only mast cell disease doctors had identified was mastocytosis, which is characterized by "abnormal proliferation and activation" of the body's mast cells -- meaning there are way too many and they act in strange ways. 

But in the last few years doctors such as Afrin have started to recognize that there are many different layers to mast cell disease. For instance, Brynn has mast cell activation syndrome, meaning her mast cells act strangely, but they're not growing in number. 

"It's like I'm living in a 24/7 allergic reaction," Brynn explains simply. 

Fruit, vegetables, milk, soy, nuts, smoke, perfume, the sun -- you name it, Brynn is allergic to it. But it's not really about the specifics; the allergens change depending on how "angry" her mast cells are that day, she says. On good days, she can eat small amounts of plain meat or mashed potatoes. On bad days, even using her feeding tube causes her extreme pain. 

Not everyone with mast cell activation syndrome has it as bad as Brynn does. "Oh God, no," Afrin says when asked. "No, no, no, no." 

But mast cells are located in your connective tissue, including your skin and the lining of your stomach and intestine. They can affect every system in the body, Afrin says, so the disease is capable of causing all the symptoms Brynn experiences.

You have to ask yourself, he says: "Is this poor patient so uniquely unlucky to have acquired so many different, independent problems? Or is it more likely that there is just one thing going on?"

Of course, having a diagnosis didn't make living with mast cell disease any easier. 

In 2012, Brynn was admitted to the hospital 30 times. She started having seizures and episodes of dystonia -- painful, violent muscle contractions that are "scary to see and scary to experience." On multiple occasions, doctors have had to put casts on her legs to prevent her joints from bending in the wrong direction.

"I've seen doctors and nurses step back, kind of like 'What is this?'" Barry Duncan says. 

Every time she went to the ER, Brynn was given a large dose of steroids to calm the inflammation. She's now steroid dependent -- and likely will be for life. 

"We could be here for days, and you still would not understand all the inner workings of Brynn and all of her medical issues," Melissa Duncan says. "But I think the underlying one is the mast cell disease, which is a beast, and continues to become a bigger beast, day by day."

 Living in a bubble

Brynn spent her 19th birthday in the hospital. An allergic reaction made her miss a zip lining trip for her 20th. On December 31, her 21st birthday, when many young adults would be out celebrating the legal drinking age with friends, she was at home still recuperating from Christmas. She had joined the holiday festivities by eating a special pizza -- made with fake bread and fake cheese. 

"It's nasty," Barry Duncan says with a laugh. "It's the worst pizza you've ever tasted." But "for her, the worst pizza you've ever had ... tastes really good."

Brynn dreams about real stuffed crust pizza sometimes. And mozzarella sticks. Occasionally she lets her spunky attitude drop, and you see that she understands the effect her illness has on those around her. 

Her parents have spent weeks sleeping in cramped hospital chairs. Her younger siblings have missed vacations and school ceremonies; they've learned how to inject Brynn with an EpiPen, and how to hold her limbs still during a dystonia episode. 

"There's a lot of guilt that goes along with having a chronic illness," Brynn says. "You feel like a burden. And people can tell you you're not, but no matter what, in your head, you feel that you are."

She has moments when she gets jealous of her high school friends who are doing all the things she can't -- attending college, moving out, finding boyfriends. She and her new friends, others with chronic illnesses she met online, have a saying: "Single and ready to mingle -- as long as you have good health insurance."

And with a giggle, the dark moment passes. Skyping with her friends keeps her spirits up. She's prolific on Instagram, with more than 5,300 followers, and writes regularly on her blog, which is called "Brynn's Bubble." 

"A lot of people with this disease ... do, in a sense, have to live in a bubble, because it's really difficult to get the symptoms under control," Brynn says. "You spend a lot of time alone. And it can be very isolating. But thanks to social media, I haven't felt alone."

Over the last two years, Brynn and her family have made progress in managing her disease. She was one of the first patients in the nation to be put on a continuous IV of antihistamine. Intravenous immune globulin, or IVIG, therapy, when a healthy donor's plasma is used to boost a patient's immune system, cut in half the number of drugs she needs. 

Of course, she still needs a lot -- a compounding pharmacy delivers a box to her house once or twice a week. The meds make her brain foggy. She punctuates conversations with "Where'd that thought go?" But that doesn't stop her from talking. She plans to keep talking until mast cell disease receives the attention she feels it deserves. 

"'You don't look sick' -- that's one of the comments that I get a lot. Or they say, 'At least it's not cancer,' and that's another hard one, because these illnesses can be just as devastating," Brynn says. "The difference is they're not understood. And the only way to change that is to somehow bring awareness to it."

Early in her taekwondo career, Brynn's instructor told her that she could win a match before it even began -- just by staring down the opponent. She plans to fight mast cell disease the same way.