sections include: symptoms of lyme disease, diagnosis and treatment
Although Lyme disease has taken on almost mythical proportions in the public mind, it is in fact a simple bacterial infection. Caused by a spirochete (a corkscrew-shaped bacterium) known as Borrelia burgdorferi, this infection is transmitted almost exclusively by bites from hardshelled Ixodes ticks. The bacteria live in a unique ecosystem—their survival requires a reservoir of infected animals, usually a combination of field mice and larger mammals such as deer, bear, and sheep. Ticks transmit the bacterium from one animal to another. When humans live or play in areas where these infected ticks reside, such as rural and suburban areas, they can become infected too.
When an infected tick attaches to a host, it ingests some blood, which triggers the spirochetes to proliferate. The multiplying bacteria ultimately spread to the tick’s salivary glands and can then be injected into the host. This sequence typically requires at least 24 to 48 hours; if a tick is attached for a shorter time, therefore, it is highly unlikely to transmit an infection. In fact, experts have estimated that only about 2 percent of bites by infected ticks result in human infection. Since the incidence of side effects from the antibiotic treatment is at least that high, doctors do not recommend routine antibiotic treatment for all tick bites.
Symptoms of Lyme Disease
If a person becomes infected with B. burgdorferi, the most common first sign is a unique rash called erythema migrans. This consists of a slowly enlarging circular or oval red rash, which surrounds the site of the initial bite. Typically the rash is not particularly painful or itchy, but if left untreated, it can grow to become many inches in diameter over the course of days to weeks. Diagnosis of this rash does not require laboratory testing since it is virtually unique to Lyme disease. Physicians usually give an infected person antibiotics immediately, which almost without exception results in a cure.
If the bacteria spread from the initial site through a person’s body, he or she may develop a fever, diffuse achiness, and a generally run-down feeling, just as with any disseminated infection. Several specific problems may arise from this early bacterial spread. Some people may develop the erythema migrans rash in several spots. About 5 percent develop irregular heartbeats or a slow pulse. Occasionally patients develop joint pains or, rarely at this stage in the illness, arthritis, with painful, red swelling of individual joints.
About 15 percent of people with the spreading infection will experience problems with their nervous systems. The most common manifestation is meningitis: an infection within the central nervous system that inflames the lining of the brain. Symptoms typically include headaches, sensitivity to light, and fever and may be mild or severe; individuals usually recover regardless of treatment, but, as with all neurologic forms of infection, antibiotics speed recovery and limit the possibility of persistent infection.
Some people suffer damage to the nerves that exit from the central nervous system. Involvement of the cranial nerves can lead to different problems, depending on the nerve affected. The most common is Bell’s palsy, a paralysis of one side of the face; on occasion this palsy can be bilateral. Involvement of other cranial nerves can result in double vision, facial numbness or pain, vertigo, hearing loss or in rare cases, difficulty swallowing or vocalizing. When the nerves exiting the spinal cord are involved, individuals can develop symptoms mimicking those of pinched nerves—severe burning or shooting pain in a limb or on the trunk, often associated with some weakness of nearby muscles or loss of sensation in the region of the affected nerve.
Other neurologic manifestations can be somewhat subtler, coming about because B. burgdorferi grows unusually slowly and does not provoke a very vigorous or effective response from our immune systems. As a result, some people may develop syndromes that evolve slowly— again with a loss of neurological function. Most common is neuropathy with damage to peripheral nerves either singly, in groups, or in widespread fashion. This leads to loss of sensation, muscle strength, or reflexes. Infected people may experience symptoms of nerve damage—burning, tingling, or other abnormal sensations. However, these symptoms must accompany other evidence of nerve damage to indicate a serious problem; when they occur in isolation, they are generally not considered evidence of a serious disease.
Similarly, B. burgdorferi infection can involve the central nervous system. In rare cases, this can be severe, with damage to the brain or spinal cord resulting in weakness or paralysis; difficulty with sensation, coordination, or sphincter function; and even alteration of consciousness. This is encephalitis. Fortunately, it can be treated, and it occurs in less than 0.1 percent of people not originally treated for Lyme disease. Like anything that damages the brain, it may cause some longterm effects. If these problems are treated early, however, they tend to be manageable.
Some patients develop alterations of memory and reasoning. In some, this is a manifestation of a mild form of encephalitis. These people’s brains often display abnormal areas on magnetic resonance imaging (MRI) scans, and their cerebrospinal fluid (CSF) is virtually always abnormal. More often, this syndrome appears in people who do not have encephalitis but rather a chronic inflammatory arthritis or other form of systemic disease. For these individuals, the problem is analogous to that seen in other non–nervous system infections—when people have a disseminated infection, they usually do not function at their intellectual best. Unfortunately, this has created a great deal of confusion and concern among individuals who perceive a decline in memory and intellectual functioning, but who lack any other evidence of Lyme disease. In such a setting, invoking a diagnosis of Lyme disease is illogical and can lead to unnecessary treatment, with significant attendant cost and potential for complications. Finally, Lyme disease does not cause psychiatric problems any more than any other comparable chronic illness.
Diagnosis and Treatment
Diagnosis of a disseminated B. burgdorferi infection usually relies on testing for antibodies created by the individual’s immune response against the offending organism. An ELISA test measures the level of antibodies in a person’s blood. A more sophisticated test, known as a Western blot, demonstrates the specific constituent proteins of the bacterium against which the antibodies are directed and is used in combination with the ELISA. The Western blot tends to eliminate much of the confusion created when antibodies are actually responding to other bacteria. However it is not as sensitive as the ELISA and is not invariably positive in all patients with Lyme disease. Interpretation requires thoughtful consideration of the two tests and the individual’s symptoms.
If a person’s central nervous system (CNS) may be infected, examining the CSF can be invaluable. This requires a spinal tap (lumbar puncture). As in all other CNS infections, a local inflammatory reaction to B. burgdorferi is almost always evident, with increased numbers of white blood cells and increased concentration of protein. Specific testing to find local production of antibodies directed against B. burgdorferi can be highly informative. Moreover, reexamining CSF after treatment can be helpful in showing a decrease in the intensity of the inflammatory reaction (decreased white count, protein), although antibody production may remain elevated for years.
Two common misconceptions about antibody testing can lead to confusion. First, it takes time for the body to generate a measurable level of antibodies. Hence, at the time of the rash, very early in infection, a test may not find any Lyme disease antibody. This does not negate the diagnosis. If the rash looks like erythema migrans, a person should receive antibiotic treatment regardless of the test result. Second, our immune systems are designed to remember past infections in order to prevent reinfection, so antibody measures typically remain elevated for years, or even permanently. Therefore, a positive test may reflect prior exposure but have nothing to do with current symptoms or how well a treatment has succeeded.
Treatment for Lyme disease is highly effective. Early in the disease, a course of oral antibiotics for three to four weeks results in a cure for about 95 percent of infected people. Doxycycline/ Vibramycin (which should not be taken by pregnant women or children under age eight) or amoxicillin is highly effective. There is good evidence that these regimens also work against more advanced forms of the disease, such as arthritis or even meningitis. For those individuals with more severe disease (typically central nervous system disease, arthritis, or other manifestations that have not responded to oral medications), doctors usually prescribe intravenous drugs—usually ceftriaxone, cefotaxime, or a very high dose of penicillin. Carefully performed studies have indicated that treatment with these medications for two weeks cures the vast majority of infections. There has been a tendency for doctors to expand this treatment to four weeks because some patients have relapsed after two. However, there are no data to indicate that routine treatment for any period longer than four weeks is either necessary or reasonable.
A partially effective vaccine against Lyme disease has been developed, but incomplete efficacy and concerns about possible adverse effects resulted in limited acceptance and withdrawal from the market. Individuals at risk of tick exposure because of where they live and work will still need to exercise caution.
In sum, Lyme disease is a somewhat unusual infection that can affect the nervous system in a variety of ways. Diagnosis and treatment are usually quite straightforward, although some controversies remain to be resolved. The best treatment is prevention—avoiding tick bites in the first place, or removing ticks carefully and rapidly after they have attached. But even if infection occurs, we are fortunate to have readily available and safe antibiotics that do an excellent job eliminating the bacteria.
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