Mathilde Ørbæk, Nitesh Shekhrajka, Rosa Maja Møhring Gynthersen, Jacob Bodilsen, Lykke Larsen, Merete Storgaard, Christian Brandt, Lothar Wiese, Birgitte Rønde Hansen, Hans R Luttichau, Åse Bengård Andersen, Helene Mens, Henrik Nielsen, Klaus Hansen, Anne-Mette Lebech, The DASGIB Study Group
OBJECTIVE: To explore pathological findings on magnetic resonance imaging (MRI) and their diagnostic implications in early-stage neuroborreliosis (NB). METHOD: Adult patients from the Danish neuroinfections cohort (DASGIB, 2015-2019) with confirmed NB, symptom duration < 6 months, and MRI performed within 14 days of diagnosis were included. MRIs were retrospectively reinterpreted by an unblinded neuroradiologist. RESULTS: In 116 patients, 123 MRIs were performed (99 brain, 44 spine, 46 with contrast). White matter lesions (WML) were common, but non-specific and associated with increasing age (p < 0.001). Six patients showed WML not typical for small vessel disease. Acute infarctions occurred in four patients. Encephalitis was clinically diagnosed in five patients; one showed brainstem FLAIR hyperintensities. In 45 contrast-enhanced brain scans, leptomeningeal enhancement was identified in 6 (13%) and cranial nerve enhancement in 29 (64%). There was poor correlation between facial palsy and enhancement. Spinal cord lesions (1.6-14 cm) were identified in 10 of 44 scans (23%) without symptoms of transverse myelitis. Among 13 contrast-enhanced spine scans, 8 showed leptomeningeal enhancement (61%), and 8 showed nerve root enhancement (61%). Most enhancements did not match symptoms. CONCLUSION: Pathological findings were found in 35 of 46 patients with contrast-enhanced MRIs. Key findings included cranial nerve, spinal nerve root, and leptomeningeal enhancement-often without clinical correlation. Spinal cord lesions were relatively frequent; cerebral infarction was rare. While key findings can support the diagnosis, their absence does not exclude NB.