Lyme Disease

At a glance

It is an infectious disease caused by a spirochete with significant immune response possibly leading to neurologic problems. Most patients consult within 7 days of the initial tick bite. The incubation period varies between 3 and 30 days. The skin lesion is characteristically an annular erythematous lesion greater than 5 cm in diameter that slowly increased in size and is painless and nonpruritic. The skin lesion is called erythema migrans and often appears as a bull’s-eye shape with a large hallow around. The second stage includes the formation of large blisters and purple skin masses. Other clinical features include fatigue, arthralgia, headache, and low-grade fever. With time, cardiovascular manifestations (AV blocks, tachycardia) and potentially severe neurological complications (encephalopathy, aseptic meningitis, cranial neuropathy—especially the facial nerve, and sensorimotor neuropathy) are seen within the first 3 months.

Synonyms

Erythema Migrans Disease; Tick-Borne Disease.

History

Named after the town of Lyme, Connecticut, USA, where a mysterious clustering of arthritis cases was reported in 1970.

Incidence

The incidence is established at 0.15 to 4.4:1,000 in the general population. The spirochete Borrelia burgdorferi that causes Lyme disease is transmitted to humans by Ixodes ticks. The nymph-stage ticks feed on humans from the months of May through July, transmitting the spirochete in the process. Endemic areas include the northeastern coastal states of the United States, Wisconsin and Minnesota in the Midwest, and the coast of Oregon and northern California. Lyme disease is the most common disease transmitted by an insect in the United States. It is also prevalent in Europe and Asia.

Genetic inheritance

There is no genetic association. It is an infectious disorder.

Pathophysiology

Results from both direct infection and the host’s immune response to the spirochete Borrelia Burgdorferi, which is carried by the tick Ixodes Dammini Scapularis. The spirochete is injected into the bloodstream through the saliva of the tick or deposited on the skin with fecal material. After incubation period of 3 to 32 days, which the spirochete may migrate to the skin, causing erythema chronicum migrans, or it may enter the bloodstream, thereby migrating to other organs. The first clinical sign of the disease can be a facial nerve palsy, followed by arthritis and a meningitis-like symptom. The late complications are probably caused by a direct effect of infection with viable organisms and the immunologic response to them. The arthritis is thought to be a result of localization of immune complexes to the synovium, resulting in joint inflammation. The B-cell alloantigen HLA-DR4 is common in patients with severe and prolonged illness, particularly arthritis or neurologic disease.

Diagnosis

Clinical evidence of erythema chronicum migrans together with symptoms of influenza or meningitis.