Amos Williams is a typical 9-year-old with a shock of brown hair who can bust out laughing just by saying "banana."

Until the rage comes.

Then his pupils dilate as if he is possessed, and he starts swearing and screaming and kicking and punching and biting and spitting. His parents restrain him to prevent him from hurting himself or his sister.

"The dark cloud comes over him and ... he becomes sinister and vengeful," said his mother, Claire Williams. "It's not him and yet it's who we are living with in those moments."

Severe flare-ups have been an off-and-on reality in the Williams home in Arden Hills since early 2022. The family felt relief this spring when they found treatment for their son's condition, which is triggered by the immune system's overreaction to colds and infections.

But they said that care is in jeopardy. Their son's M Health Fairview doctor is stepping down — and nobody else is stepping up.

The coming departure of Dr. Bazak Sharon on Nov. 15 has stunned Minnesota families whose children have conditions known as PANS or PANDAS. The U initially gave them two weeks to find other doctors, then agreed to maintain treatment through 2023. After that, parents may take their children out of state or exhaust savings at a local out-of-network clinic.

Few doctors seem interested in treating the condition and taking on frustrating children, distraught parents and insurance battles, Williams said. "There is a lot of hot potato going on," she said.

PANDAS is an acronym for a neuropsychiatric disorder touched off by strep throat. PANS is similar but associated with other infections. Both involve an immune response — perhaps to a combination of viruses and bacteria — that evokes physical tics and aggressive and compulsive behaviors.

Sally Rafowicz likened her 22-year-old son to an "uncaged tiger" whose symptoms emerged after he contracted strep in grade school. The scent of his sister's yogurt could turn him into a "berserker," she said.

"They are so powerful, physically, in that rage," she said. Treatment prevents his episodes.

Medical centers such as Stanford and the University of Arkansas have PANS/PANDAS clinics, but others aren't sold on how to treat it, or whether it exists. Some doctors say it is a form of Tourette syndrome or autism. Mayo Clinic's exhaustive library of diseases doesn't list it, but Wisconsin researchers this year estimated that it strikes about 1 in 12,000 children ages 3 to 12.

Antibiotics and steroids appear to help, along with immunoglobulin infusions that reset patients' out-of-whack immune systems. But doctors don't know precisely what the drugs do, and they lack clinical trials to prove that the benefits outweigh risks.

"I can count on my fingers the number of scientists in the field," said Dritan Agalliu, a neurological researcher at Columbia University Medical Center in New York. He is studying how the immune system's critical T-cells overcome the brain's protective barrier and become toxic.

Sharon said he first heard of PANDAS in medical school and encountered a few cases as a hospitalist and infectious disease specialist at M Health Fairview's University of Minnesota Medical Center. As medical director of the U's pediatric COVID-19 clinic, he started to see more cases during the pandemic — especially last fall when RSV infections surged.

"That was the exclamation mark that, 'Yes, it's a thing!' I might not understand it, but I know what it looks like," he said. The doctor then reported "remarkable" results with immunoglobulin infusions, which are costly because they amass antibodies from multiple blood donors to dilute or counteract patients' own harmful antibodies.

Sharon said he feels terrible for his PANS/PANDAS patients but that he resigned from University of Minnesota Physicians because of an unrelated dispute over the clinical management of head trauma in infants.

The U in its correspondence steered families to a Madison, Wis., clinic.

"Given the prolonged process of recruiting and credentialing physicians, the responsible step is to direct patients to a clinic that already has established the unique care they may be seeking," said Dr. Joseph Neglia, the U's chair of pediatrics.

Alternatives include a nurse practitioner at Newbridge Health & Wellness in Edina, which typically doesn't bill insurance — leaving families to pay thousands of dollars out of pocket.

Brittny Vollmer and her husband have exhausted savings and are accruing credit card debt to continue treatment of their three sons.

They can no longer afford out-of-pocket treatments at Newbridge, so they are considering flying their sons to a clinic in Colorado that accepts health insurance.

Vollmer is a nurse practitioner in the southwest metro and has thought of opening a PANDAS clinic, but not now. It would be exhausting, she said, while managing the time-consuming care of her sons to prevent any more flare-ups and outbursts.

"It makes me emotional when I think about how things used to be," Vollmer said after looking at pictures of her kids smiling and laughing when they were younger.

Minnesota lawmakers in 2019 mandated coverage of treatment for PANS/PANDAS, but it governs only public and fully insured plans — not self-funded plans used by many large employers.

Williams and her husband fought for months to get coverage of immunoglobulin, only to learn after one infusion that they were losing access to their doctor. They are flying their son to California to try to resume treatment.

The flare-ups are traumatic, but Williams said it is equally hard watching her son in the aftermath — unable to understand his rage and overwhelmed with shame. A video showed him sobbing and hiding behind a piano after one episode at home.

"I'm not even a me," he wailed. "I'm just a bad thing inside a body."

Inconsistency is a problem. Some children with PANS/PANDAS have the same antibodies in their blood, which could be used to diagnose the condition. Others don't. Some children benefit from single treatments while others progress over years — or only until their next infections.

But many get better. Natalie Barnes, a nurse, and her son were featured in a 2018 ABC News story on PANS/PANDAS.

The news program showed her son, who was 11 at the time, screaming, lashing out and shaking his head and arms. With treatment, he is on schedule to graduate from high school and has signed up for cross country this fall. Barnes said it was thrilling just watching him cross a finish line.

"No one else understands," she said, "but this is like winning the Olympics."