Lyme disease or Lyme borreliosis is a spirochettal disease, whose etiological agent, the bacteria Borrelia burgdoferi, is transmitted by ticks. The bacteria spreads hematogenously, thus determining the three stages of the disease.

The signs and symptoms in the first stage of Lyme disease consist in cutaneous manifestations. After the incubation period, which lasts up to 30 days, erythema migrans, the characteristic, expanding skin lesion appears at the site of the bite. The erythema migrans is at first a red macule but in time it slowly expands to an anular lesion with a bright red outer border and central clearing. In some cases the center of the lesion may become necrotic, vesiculous or erythematous. This type of lesion is not usually painful. The most common sites of erythema migrans are thigh, axilla and groin, but the lesion may virtually be located anywhere.

In the second stage of Lyme borreliosis the bacteria spreads hematogenously to many sites. The early signs and symptoms of the disease are usually changing and sometimes intermittent, except for fatigue which is constant. The most common symptoms in this stages are skin lesions, fever, severe headaches,chills, musculoskeletal pain, malaise, arthralgias.

Less common features of the disease are: hepatitis, lymphadenopathy, splenomegaly, iritis, nonproductive cough, dyspnea and sore throat.

In this stage it may appear symptoms suggesting meningeal irritation and after several weeks up to 15% untreated patients present neurological abnormalities such as meningitis, encephalitic signs, radiculoneuropathy, myelitis an cranial neuritis. A serious complication of neurological involvement happens in children, where due to the inflammation and the increased intracranial pressure the optic nerve may be affected, leading to blindness.

Another 8% of the untreated patiens develop cardiac symptoms, the most common cardiac abnormality being atrioventricular block, myopericarditis and chronic cardiomyopathy, pancarditis and cardiomegaly.
A very common feature of Lyme disease in this stage is articular and musculoskeletal pain. This typical feature consist in migratory pain in muscles, joints, bones, and tendons.In the third stage of the disease , several months after the infection more than 60% of the untreated patients develop arthritis. This feature usually presents as intermittent attacks of oligoarticular arthritis, especially in large joints (most commonly the knee).

A less common feature, chronic neurologic involvement may also manifest. The most common forms of neurological involvement are:encelopathy affecting mood, memory and sleep and axonal polyneuropathy (manifested as distal paresthesia or spinal radicular pain).In this stage of the disease the late skin manifestation is acrodermatitis chronica atrophicans. This lesion usually begins with reddish-violaceous discoloration; over the years it becomes sclerotic or atrophic.