Actor Reveals Rare Disease Diagnosis After Complex History

Kelsie Mathews has lived with more health challenges in her 39 years than most people face in a lifetime. The actor, musician, and performer has dealt with endometriosis, lupus, breast tumors, fibromyalgia, seizures, and a rare disease that affects an estimated 32,000 people in the United States. Last October, the Los Angeles resident added systemic mastocytosis to her list of diagnoses.

Mathews said she is up to eight different diagnoses at this point. Because of her complex medical history, the road to a systemic mastocytosis diagnosis was not straightforward.

The first sign that something was wrong came in 2021, four years before her diagnosis. Mathews developed sudden, unexplained swelling. She swelled up over 100 pounds of fluid in a week. When her feet turned purple and became too swollen to fit into her flip-flops, she went to the emergency room.

Mathews recalled the doctor saying, ‘Oh, some people are just more prone to swelling.’ She thought it was her heart or something, but it didn’t make sense to her.

Over the next few years, new symptoms kept appearing. Hot baths that once helped ease her endometriosis pain suddenly left her covered in hives. Lesions spread across her body and lasted for months. Gastrointestinal problems became more frequent. While working an event one day, she became so sweaty that people stopped to ask if she was okay.

Mathews said she couldn’t stop sweating and was feeling lightheaded and dizzy.

At the time, none of the symptoms seemed connected. Because she was already living with several chronic health conditions, it was difficult to know what was causing what. The first major clue came after a colonoscopy and endoscopy revealed abnormal mast cells in her colon.

When the gastroenterologist called to tell her he suspected systemic mastocytosis, he said he would refer her to a hematologist-oncologist for additional testing. Mathews realized she had been having allergic reactions to hot water and swelling, and it was a profound moment for her because she didn’t feel crazy anymore.

After blood work and a bone marrow biopsy, Mathews received an official diagnosis from City of Hope in October 2025.

Shortly after her diagnosis, Mathews was prescribed avapritinib, an oral medication approved to treat adults with advanced and indolent systemic mastocytosis. Because her symptoms were severe, her care team started her on the highest dose possible.

They put her on the highest dose of avapritinib, but within three weeks, she ended up back in the hospital because she was having terrible side effects.

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She experienced fatigue, nausea, and diarrhea, and her long, red hair suddenly turned white at the roots and fell out in clumps.

Mathews said it was just so much.

Looking for answers, she requested a referral to see a systemic mastocytosis specialist at Stanford Medical Center. A friend joined her for the 16-hour round-trip drive.

Mathews cried a lot, but the doctor at Stanford was empathetic and told her she wasn’t crazy.

Her doctor at Stanford is now coordinating with her team at City of Hope and working to enroll her in a clinical trial for bezuclastinib, an investigational treatment under review by the U.S. Food and Drug Administration.

He’s trying to get her on it faster, so she doesn’t have to wait until December.

Living with systemic mastocytosis has taught Mathews the importance of advocating for herself. Because the disease is rare, many people, including healthcare providers, have never encountered it before.

Mathews said people don’t understand systemic mastocytosis, and when she tries to explain what’s happening to her, they say it doesn’t make sense.

She has been dismissed in medical settings, including emergency rooms, because some healthcare providers are unfamiliar with the disease.

Mathews said living with a rare disease can feel isolating, especially when others assume all cancer treatments look the same.

People think that’s just normal for all cancers, but it’s not the same, and it’s isolating.

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To help with that isolation, Mathews joined an online support group earlier this year. Connecting with others who have had similar experiences helps her feel understood, and they have the same symptoms and the same story as her.

Mathews didn’t want to join a group, she just wanted to hide from the world, but she’s glad she joined, and it’s been very helpful.

As her symptoms worsened, Mathews could no longer keep up with the long days required on film sets or touring for live performances, which forced her to take a break from her career.

Mathews always was in front of the camera, behind the camera, or on stage, but she’s had to take a step back because her body doesn’t have that capability anymore, and she only gets about two good hours a day.

While she has stepped away from performing, she hasn’t stopped creating, and she continues to write music, which has always been her therapy.

Mathews misses creating and being able to perform, but she’s learned to rely on humor to cope with her situation.

Her palliative care doctor actually wrote in her chart that she continues to use humor to cope with her situation.

Throughout her health challenges, Mathews said her friends have been a constant source of support and comfort, walking her dogs, bringing her meals, driving her to medical appointments, keeping her company in the hospital, helping pay bills, and stepping in whenever she needs them.

Mathews said she would not be surviving right now if she didn’t have her friends, and she’s very lucky to have found her tribe.

Accepting that support hasn’t always been easy for Mathews, but she said learning how to ask for and accept help is essential when you’re living with a rare disease, and she is showing up for others in the same way her friends have shown up for her.

Mathews has become increasingly public about her health journey because she wants others living with systemic mastocytosis to know they’re not alone, and she invites people with systemic mastocytosis to reach out if they need information or someone to lean on, including medical guidance and support.