"Black scabs were coming out of her skin," said her mother, Kathy Gary. "The nails would grow so long and come out and regrow themselves. They are hard to touch and stick you."
The disease so far has affected not only her skin, but her bones and her vision. Because Isom is unable to walk without a cane, her mother helps her out of bed each day.
Doctors at Johns Hopkins Medical Center in Baltimore, where Isom is being treated, told her family that she is the only person in the world with this unknown condition.
And now she has $500,000 in unpaid medical bills. Isom has state insurance, but it doesn't cover medical care in Maryland. Her mother lost her job as a medical receptionist because she looks after her daughter at home, so savings have dried up.
(Handout/Shanyna Isom)Once a month, mother and daughter travel to Baltimore from Memphis to monitor her treatment.
But now, Isom has put all of her energy into creating the S.A.I. Foundation (so named for her initials) to help others with mystery illnesses.
Bank of America has agreed to take donations at any of their branch offices. Friends have organized fundraisers, and her high school has dedicated a football game to her charity.
Despite her debilitating illness, Isom told ABCNews.com, "I don't know whether to smile or cry. I am very blessed."
On her blog, Pray for Shanyna, she laments: "It has taken all of my hair out and has left my body with scabs all over it, plus I have lost about 200 pounds. Two years ago, I was a healthy woman on my own ... had big dreams and goals that I was following until one day my body completely shut down on me."
Isom was a junior studying criminal justice when the mystery illness first occurred in September 2009, according to WLBT in Memphis, which first reported the story.
She went to an emergency room for an asthma attack and was given a large dose of steroids, which doctors suspected caused an allergic reaction.
After returning home, Isom began itching. Doctors prescribed Benadryl, but it got worse.
"It was uncontrollable and we didn't know what it was," said her mother.
Soon, her legs turned black.
"It looked as if she had been in a house fire and gotten burned," said Gary.
Doctors thought she had eczema or a staph infection and prescribed drugs, but it got worse. Meanwhile, all tests came back negative.
"We could not figure out what was going on," said her mother. "She was just breaking out everywhere. Her body was scabbed all over."
At the same time, Shanyna was losing 10 to 15 pounds a week. A bone marrow biopsy turned up nothing.
It was then her Memphis doctor threw up his hands.
"He said she would be like that for the rest of her life," said Gary. "But I couldn't accept that."
Isom and her family persisted, and in August 2011, Shanyna went to Johns Hopkins.
There, doctors determined that she was producing 12 times the number of skin cells in each hair follicle. Instead of growing hair, the follicles were producing human nails.
Doctors think her skin isn't getting enough oxygen -- she is also lacking sufficient amounts of vitamins A, B, C, D and K, according to her mother.
But with treatment, she is improving.
"Her legs aren't covered in black scabs," said her mother. "They are looking better, and her face just looks like she has a real bad sunburn."
25 Medicines and Still No Cure Today Isom is on 25 medications, but her insurance only pays for five of them. She is awaiting the results of genetic tests that may give doctors clues to what is wrong.
"The doctors are so caring," said Gary. "It's just amazing how much they have done for her. We really didn't think she was going to make it."
Isom said she slipped into a depression, but now feels uplifted by the support of family and friends.
"I know it's a blessing that I can reach out and touch people's hearts," she said.
She remembers the day at Johns Hopkins when she felt sorry for herself, shuffling through the corridors on a walker.
"I saw a little girl, 4 or 5 years old, and she was walking through the same hall and had the biggest smile on her face," said Isom. "She had braces from [her] hip to her feet and had a walker and held her head up so high. I thought, 'If she can, I can. I had a life. This baby is trying to have a life.' ... I fed off her energy."
Isom said she prayed, "I will never be selfish again."
Gary said their ordeal has been a "nightmare ... to see her whole body shut down."
But she gets her strength from her daughter.
"Shanyna is remarkable," said Gary. "She has been able to hold her head high. I keep telling her we are going to make it, through the grace of God."