Infection causing behaviors

In today’s post, I’m tracing a line from a 17th-century observation to what many families are living through right now. Same pattern, new name — and help is possible.

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A 17th-Century Clue

In 1686, a London physician named Thomas Sydenham—now known as the English Hippocrates—described something strange happening in otherwise healthy children.

Out of the blue, these kids would begin writhing, flailing, and twisting their bodies. Their emotions would spiral too — they might sob uncontrollably, laugh hysterically, or have huge outbursts of aggression.

Sydenham called it St. Vitus dance. He couldn’t explain why it happened — this was the 1600s, after all — but his detailed description turned out to be the first record of something we still recognize today.

Hundreds of years later, we know those odd, jerky movements (called choreiform movements) are one of the hallmark symptoms of rheumatic fever, which is caused by strep bacteria.

What Sydenham saw — and what we continue to see — is that an infection can cause neurological and psychiatric changes. Children who were once healthy suddenly developed obsessive thoughts, abnormal movements, or bursts of aggression — all traced back to a strep infection.

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The Modern Connection

Today we understand that strep and other infections can trigger inflammation in the brain, leading to dramatic shifts in mood, behavior, and function. Two of the best-known conditions in this category are PANS (Pediatric Acute-onset Neuropsychiatric Syndrome) and PANDAS (Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal infections).

These children often experience a sudden, overnight change — one day they’re fine, the next they’re flooded with anxiety, OCD-like behaviors, emotional instability, or even tics. Parents often describe it as if their child was “possessed” or “replaced.”

The trigger? The immune system, trying to fight infection, mistakenly attacks the brain, particularly regions involved in emotion, movement, and decision-making.

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Why It Matters

The brain and immune system are in constant conversation. When that communication goes awry, it can look like mental illness — but the underlying cause is often inflammation, not intention.

This is why it’s so important for physicians to look beyond behavior alone and consider medical triggers for psychiatric symptoms, especially when the onset is abrupt and extreme.

The challenge is that many families go from doctor to doctor hearing, “It’s anxiety,” “It’s just OCD,” or “They’ll grow out of it.” Meanwhile, the root cause — immune dysfunction from infection — goes unaddressed.

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What We Can Learn from History

Sydenham didn’t have the tools we have now — no lab tests, no MRI, no antibiotics — yet his careful observation revealed a pattern we can still learn from: infection-driven brain changes are real.

We’ve just given them new names.
We’ve built better science around them.
And we now know how to treat them with compassion and precision.

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Moving Forward with Hope

Families dealing with PANS or PANDAS often feel isolated and misunderstood. But you’re not imagining it. There’s centuries-old evidence — and modern medical understanding — that back up what you’re seeing in your child.

Healing starts with awareness, accurate diagnosis, and comprehensive care that addresses both infection and inflammation.

And as we keep learning, we can offer these kids what Thomas Sydenham couldn’t: a path back to themselves.

Note: We do see these children and their families in our clinic and recently started accepting some insurances for these visits. These are specialized visits and we have limited availability but are happy to do evaluations and management for these amazing kids and families. To get started, fill out this contact us form so our team can see how we can help.

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