Clinical Manifestations and the Role of Visual Diagnosis in Early-Stage Lyme Borreliosis
The diagnosis of Lyme disease, caused primarily by the spirochete Borrelia burgdorferi, begins with a rigorous clinical evaluation.
In the early localized stage, the most definitive diagnostic marker is the Erythema Migrans (EM) rash. This skin lesion typically appears within 3 to 30 days of a tick bite and is pathognomonic—meaning its presence in an endemic area is sufficient for a clinical diagnosis without the need for supplemental laboratory testing.
A standard EM rash expands over several days, often reaching a diameter of more than 5 cm. While frequently described as a "bullseye" with central clearing, many EM rashes are uniformly erythematous (solid red). Because the immune system has not yet produced a measurable quantity of antibodies during this early phase, blood tests often return false negatives. Therefore, healthcare providers are trained to initiate antibiotic treatment immediately upon visual confirmation of the rash to prevent the bacteria from disseminating to the nervous system or joints.