Thermographic Assessment of Lyme Borreliosis Without Erythema Migrans.

Background: In 11-18% of patients, infection with Borrelia is not accompanied by the characteristic skin lesion known as erythema migrans, complicating the timely diagnosis of Lyme borreliosis. To aid in identifying this atypical presentation, we assessed the tick bite site with thermographic imaging.

Aim: To determine the diagnostic value of infrared thermography in patients with Lyme borreliosis without erythema migrans.

Materials and methods: We observed 16 patients with Lyme borreliosis without erythema migrans. The diagnosis was based on a history of tick bite and laboratory confirmation using two-tiered serological testing, performed 10-20 days after tick exposure. Thermographic imaging was performed with the device positioned 100-150 cm from the area of interest. Temperature differences (ΔT) were recorded.

Results and discussion: Thermographic imaging revealed localized hyperthermia in all 16 patients at the site of tick attachment, presenting as annular thermal changes (ΔT = 0.6-3.8 °C) that persisted for at least two weeks, even with ongoing antibacterial therapy. Nearly one-third of patients had ΔT in the range of 0.6-1.1 °C, half showed values of 1.2-1.6 °C, and in 18.7% of cases, ΔT exceeded 1.6 °C. These measurements were obtained and quantified using software-assisted analysis of the thermograms. Therefore, the absence of visible erythema migrans does not rule out localized inflammatory changes: centrifugal spread of Borrelia from the bite site can still induce subclinical cutaneous inflammation detectable with infrared thermography.

Conclusion: Infrared thermography of the tick bite site can reveal a "thermal erythema migrans" pattern, an annular zone of hyperthermia corresponding to the distribution of erythema migrans even when no rash is visible on clinical inspection. This early thermographic sign, detectable when a temperature exceeds 0.5 °C between the bite site and adjacent or symmetrical areas, may support timely initiation of etiotropic therapy to prevent long-term complications of Lyme disease.