Aug. 23 issue - What do you call a headache that lasts five years? Andy Eckl of Trumbull, Conn., came down with a skull-splitter in 1997, when he was 5 years old, and he got no relief until he was 10. He muscled through first and second grade on Advil, but by third grade the pain had spread to his joints, and by fifth grade it had taken over his life. "The other kids were all learning how to throw and catch," his mom, Nancy, recalls. "Andy could barely walk." Suspecting migraines, family doctors prescribed Maxalt and moved on to Neurontin and Depakote (anticonvulsants that some patients find helpful), but nothing made much difference. Finally, a homeopath advised the parents to get Andy tested for Lyme disease. The results were negative—but blood tests can't rule out Lyme, so an infectious-disease specialist prescribed antibiotics anyway. Andy got his first dose on Nov. 11, 2002, and by Nov. 16 the pain had lifted. The headache from hell wasn't a migraine after all. Chances are, the whole thing was caused by a tick bite.

Lyme disease is nothing unusual in places like Trumbull. Every summer brings an onslaught of new cases as ticks spread the bacterium Borrelia burgdorferi from birds, mice and chipmunks into people (deer carry ticks but they don't get the infection). In its classic form, Lyme starts with a bull's-eye rash and causes a flu-like illness that responds quickly to oral antibiotics. But experts are now developing a far scarier picture of Lyme disease. When the infection goes unrecognized—or doesn't respond to treatment—it can become a chronic and devastating neurological condition. Some patients are hobbled by fatigue and arthritis, others by depression or anxiety. Still others suffer memory loss or even psychosis. "Lyme disease is the new 'great imitator'," says Dr. Brian Fallon of Columbia University and the New York State Psychiatric Institute. That's the term doctors once used to describe syphilis when it caused psychiatric illness.

Like the syphilis bacterium, the Lyme microbe can escape the bloodstream through vessel walls and invade the heart, brain and nervous system, where it causes persistent inflammation. Fallon is now using nuclear imaging techniques to gauge the effects on patients' brains. Viewed through an MRI scanner, some of them display lesions typical of multiple sclerosis. Other tests, known as PET and SPECT, reveal uneven blood flow and glucose metabolism—a common sign of vascular inflammation. "You don't see that in a healthy brain," Fallon says. "It's associated with conditions like lupus, HIV and chronic cocaine abuse."

No one knows exactly how Borrelia burgdorferi causes all this trouble. It's possible that some patients remain chronically infected, while others suffer from persistent inflammation after the infection itself is gone. And each type of patient may need a different type of care. Most people with advanced, neurological Lyme disease get better after four weeks of intravenous antibiotics, but some 40 percent either fail that regimen or relapse after responding to it. Alice Levitt got sick at the age of 11 while growing up in Greenwich, Conn., and suffered for five years before she was diagnosed in 1997. After six years of failed antibiotic therapy, she had the good fortune to meet Dr. Amiram Katz, a Yale neurologist with a private practice in Orange, Conn. Katz used an experimental regimen of intravenous immunoglobulins (naturally occurring antibodies) to tame her overzealous immune system, and within a month Levitt had her life back. Now 23, she lives in Essex, Vt., where she is working for a theater company and writing a musical comedy. "I've ended up in such a good place," she says. That should encourage anyone haunted by the new great imitator. Unfortunately, many sufferers still don't know they have Lyme.