Causes of Lyme Disease
Lyme disease is caused by bites from an infected tick. The human body mounts a reaction to the infecting organism that triggers production of inflammatory agents throughout the body. These "inflammatory agents" are the chemicals produced by the body's immune system that normally fight off infection.

Symptoms of Lyme Disease
Doctors divide the symptoms of Lyme disease into three phases: early localized, early disseminated, and late disease. The three phases of symptoms can overlap. Many patients never show early symptoms at all.

Early localized disease refers to a red rash in the area of the tick bite. This rash shows up within a month of infection. The bite itself is usually found near the waist or belt line, or in other warm, moist areas of the body. The bite may burn, itch, or hurt. The rash usually grows over a period of days and may be in a "bulls eye" pattern, red with a white spot in the middle, or completely red.

Most patients with early localized Lyme disease also complain of flu-like symptoms, such as headaches, fatigue, and muscle and joint pain.

Early disseminated disease shows up days to months after the tick bite. Patients may not remember any rashes or bites. The most common symptoms of early disseminated disease are cardiac and nervous system problems. Some patients who have the rash and are not treated with antibiotics develop heart problems. These may include heart blockage and weakening of the heart muscle. Heart symptoms may clear up on their own.

Some patients who don't receive antibiotics develop damage to the nervous system. Neurologic symptoms also tend to go away on their own, but very slowly. These neurologic symptoms can include meningitis and headaches. Individual nerves can be affected causing numbness, weakness, and pain in the areas the damaged nerve travels.

Late disease symptoms develop months or even years after the tick bite. Some patients who have late disease symptoms have never had any other symptoms of Lyme disease. Late disease causes arthritis pain that comes and goes in many joints. People with late Lyme disease may develop chronic arthritis of one knee.

Many patients who have had Lyme disease describe headaches, fatigue, and joint pain that can last for months after treatment. These problems generally go away without any extra treatment, but very slowly.

Doctors diagnose Lyme disease based on your health history and a physical exam. Your doctor may order blood tests, but they are only used to confirm the diagnosis. The techniques used to test your blood are called ELISA and Western blot. Both tests can sometimes give false positive or unclear results. If you have had the infection for less than six weeks, your body may not even be making enough antibodies to be detected in the tests.

In very rare cases, the lubricating fluid of a joint (synovial fluid) or spinal fluid may need to be analyzed to confirm Lyme disease.