These symptoms can last for years after the patient has been given the all-clear after successful high-dose antibiotic therapy.
It's been believed the drugs can reverse Lyme disease—which is caused by a tick bite—if it can be treated within the first month or so.
But researchers from Johns Hopkins Medicine have used brain scans to discover that around 10 per cent of those successfully treated had brain inflammation that caused debilitating fatigue, pain, insomnia and 'brain fog'.
The sufferers, who had been diagnosed with PTLDS (post-treatment Lyme disease syndrome), had high levels of a chemical marker that indicated widespread brain inflammation.
Although researchers knew that PTLDS sufferers had chronic inflammation, they didn't know it accumulated in the brain. The Johns Hopkins researchers used a sophisticated PET (positron emission tomography) scanner to see for the very first time just where the inflammation was happening. They compared the scans of 12 PTLDS patients against those from 19 healthy controls and found that the patients had signs of inflammation in eight regions of the brain.
Their discovery proves that PLTDS fatigue and cognitive problems has a real biological cause and isn't just 'in the mind', as some doctors have believed, the researchers say.
It doesn't explain other symptoms of PLTDS, such as muscle weakness, the researchers added.
Lyme disease is a bacterial infection caused by tick bites. Around 300,000 Americans are diagnosed with the condition every year.