Dr. Philip McMillan,  John McMillan

On a December morning in 2022, Princess Bajrakitiyabha was out in a field training her dogs, seemingly healthy and full of energy. By that evening she had collapsed into cardiac arrest, and she never woke up. She stayed unconscious for three and a half years before she died on the 12th of June 2026, at the age of 47.

She was no ordinary patient. The eldest daughter of Thailand’s king, she was a lawyer and diplomat who spent her career championing justice and women’s rights, and who helped advance the United Nations Bangkok Rules for women prisoners. A nation grieved her. But some of the doctors following her case felt more than grief. To them, the official story never quite held together.

That story rested on a single diagnosis: mycoplasma pneumonia-associated myocarditis, a bacterial chest infection that can, in rare cases, inflame the heart muscle badly enough to stop it. It reads cleanly enough on a death certificate. It also runs against most of what is known about how the infection actually behaves. The account had shifted once already, too. The first explanation offered for her collapse was a brain hemorrhage, quietly dropped in favor of the mycoplasma diagnosis when no bleeding could be found.

Professor Sucharit Bhakdi, a microbiologist who met with senior Thai advisers soon after the collapse, was willing to say so out loud. He pointed out that the princess had received a third COVID-19 shot around twenty-three days before she fell ill, and he dismissed the bacterial explanation on mechanical grounds rather than political ones.

“There is not a single known case of mycoplasma myocarditis that develops within hours and causes cardiac arrest. It can’t happen,” Bhakdi said.

The timing is what makes the case so unsettling. A woman well enough to train dogs in the morning does not, as a rule, suffer fatal heart failure from a creeping bacterial infection by nightfall. That speed points toward something already waiting in the tissue, not something slowly working its way in from the lungs.

What “Walking Pneumonia” Usually Does

It helps to know what mycoplasma pneumonia normally does, because the distance between the usual case and this one is vast. Most people who catch it barely break stride. Doctors even call it “walking pneumonia,” since the typical course is a dry cough, a fever, a sore throat and some fatigue while ordinary life carries on. The organism comes in through the nose, settles in the lungs, and tends to stay there.

Now and then it spreads further, into the heart, brain, skin or blood, and when it reaches the heart it can set off myocarditis. The patients who end up that sick, though, are almost always gravely ill and already in a hospital bed by the time the heart becomes involved. They are not out walking their dogs an hour before they arrest. Nothing in medicine is ever flatly impossible, but a great deal of it is improbable, and weighing that improbability is most of what diagnosis really comes down to.

A Diagnosis Reached With a Line Missing

A case published in 2024 shows how easily that weighing can fail. A healthy 29-year-old man came into an emergency department with palpitations, breathlessness and an odd fullness in his abdomen after four days of feeling unwell. His oxygen had fallen to 89 percent. His heart was enlarged and failing, with an ejection fraction of just 30 percent and fluid backing up into his lungs. A blood marker of heart strain had climbed past 9,000, the reading of a heart in serious trouble. Tests came back positive for mycoplasma, and the chart duly read “mycoplasma myocarditis.”

One detail on the scan should have given the team pause. Parts of the heart muscle were no longer contracting properly, a finding called regional wall motion abnormality, and it usually points to damage from some time ago rather than to an infection picked up the previous week. A four-day cough rarely leaves a mark like that. Yet the man’s vaccination status appears nowhere in the report. It was not recorded, not weighed, not entered as one of the possibilities worth ruling out. Sound medicine runs on the differential diagnosis, the working list of every condition that might account for what the doctor is seeing, each one tested and ranked by likelihood. When the most plausible cause is missing from that list, the conclusion is compromised before it is even reached.

The Scars No One Went Looking For

The strangest evidence of all has gone almost entirely unnoticed. In early 2025, a team of Japanese pathologists published an autopsy study of three people who had died of unexplained cardiac arrest. Their hearts held something the pathologists had never encountered: many small scars scattered through the muscle, quite unlike the single broad scar a heart attack leaves behind. Across roughly thirty years of clinical pathological conferences, they wrote, microscars of this kind, in hearts with no history of heart attack, had simply never turned up. All three patients had been boosted.

A result that unusual ought to have sent a jolt through cardiology. Instead it has been cited only about six times, a couple of those by one physician who grasped its weight. Work that should be anchoring hundreds of follow-up studies has been left to sit.

The Question Medicine Won’t Ask

Dr. Philip McMillan, who has gone through these cases closely, makes the point that an answer in the princess’s case was always within reach. A full autopsy was not even necessary. A simple punch biopsy of her heart muscle could have shown whether her tissue carried the same scattered microscars the Japanese team had found. The means were there the whole time, and they went unused.

“Without the autopsy research, we are just blowing in the wind. Nothing will make a difference because the critical research that needs to be done has not been done,” McMillan said.

This is the part that lingers. A woman who was well one morning was gone by night, handed a diagnosis the underlying biology struggles to support, and then never examined in the one way that might have told her family what really happened. Would they not want to know? Her situation is admittedly tangled, three and a half years of further illness piled on top of the first collapse, so a clean answer may no longer be possible. The trouble, though, runs deeper than any single patient.

Somewhere tonight another person will drop without warning, and a family will be handed a tidy label that closes the file rather than opening it. The tissue that might explain it will be buried with no one having looked, and whatever pattern connects these deaths, if a pattern is there at all, stays out of sight for want of a few biopsies. The hard part was never the science. The hard part is finding someone with the authority to ask the question and the will to follow where it leads. Until then it simply hangs there, unanswered.