Lyme disease overview

Overview
Lyme disease, or borreliosis, is an emerging infectious disease caused by spirochete bacteria from the genus Borrelia. The vector of infection is typically the bite of an infected black-legged or deer tick, but other carriers (including other ticks in the genus Ixodes) have been implicated. Borrelia burgdorferi is the predominant cause of Lyme disease in the US and Borrelia afzelii and Borrelia garinii are in Europe.

The disease presentation varies widely, and may include a rash and flu-like symptoms in its initial stage, then musculoskeletal, arthritic, neurologic, psychiatric and cardiac manifestations. In a majority of cases, symptoms can be eliminated with antibiotics, especially if treatment begins early in the course of illness. Late or inadequate treatment often leads to "late stage" Lyme disease that is disabling and difficult to treat. Controversy over diagnosis, testing and treatment has led to two different standards of care.

Diagnosis
Due to the difficulty in culturing Borrelia bacteria in the laboratory, diagnosis of Lyme disease is typically based on the clinical exam findings and a history of exposure to endemic Lyme areas. The EM rash, which does not occur in all cases, is considered sufficient to establish a diagnosis of Lyme disease even when serologies are negative. Serological testing can be useful, but is not diagnostic.

Clinicians who diagnose strictly based on the U.S. Centers for Disease Control (CDC) Case Definition for Lyme are in error, as the CDC explicitly states that this definition is intended for surveillance purposes only, and is "not intended to be used in clinical diagnosis."

Importantly, virtually no controlled studies of late lyme encephalopathy have been performed, and the CDC diagnostic criteria were not formulated for use on this entity. Once lyme disease is well established in the brain, it can occur as a very disabling diffuse encephalopathy which however is difficult to diagnose using standard serological or intrathecal testing for reasons outlined below. Lyme is a deep tissue infection and by the time encephalopathy is established, few if any CFS antibodies can be detetected, and PCR is unreliable. Seronegative disease can occur for the same reason that this phenomenon occurs in neurosyphilis, with incomplete or intercurrent antibiotic treatment abrogating the serum antibody response, but not eliminating the infection.

It is in this context that advanced imaging studies like SPECT or PET can provide objective evidence of global brain dysfunction. Resort is often made to neuropsychological testing, but a normal result does not rule out the illness, which can be very subtle and manifest as a disabling mood disorder accompanied by massive and debilitating fatigue, with few objective signs.

Diagnosis of late-stage Lyme disease it is often difficult due to the multi-faceted appearance which can mimic symptoms of many other diseases. For this reason Lyme has often been called the new "great imitator". Lyme disease may be misdiagnosed as Multiple sclerosis, rheumatoid arthritis, fibromyalgia, chronic fatigue syndrome (CFS), or other autoimmune and neurodegenerative diseases.