Enhancement of cranial nerves in Lyme neuroborreliosis: incidence and correlation with clinical symptoms and prognosis

Abstract

Purpose: Symptoms of cranial neuritis are a common presentation of Lyme neuroborreliosis (LNB). Imaging studies are scarce and report contradictory low prevalence of enhancement compared to clinical studies of cranial neuropathy. We hypothesized that MRI enhancement of cranial nerves in LNB is underreported, and aimed to assess the prevalence and clinical impact of cranial nerve enhancement in early LNB.

Methods: In this prospective, longitudinal cohort study, 69 patients with acute LNB were examined with MRI of the brain. Enhancement of cranial nerves III-XII was rated. MRI enhancement was correlated to clinical findings of neuropathy in the acute phase and after 6 months.

Results: Thirty-nine of 69 patients (57%) had pathological cranial nerve enhancement. Facial and oculomotor nerves were most frequently affected. There was a strong correlation between enhancement in the distal internal auditory canal and parotid segments of the facial nerve and degree of facial palsy (gamma = 0.95, p < .01, and gamma = 0.93, p < .01), despite that 19/37 nerves with mild-moderate enhancement in the distal internal auditory canal segment showed no clinically evident palsy. Oculomotor and abducens nerve enhancement did not correlate with eye movement palsy (gamma = 1.00 and 0.97, p = .31 for both). Sixteen of 17 patients with oculomotor and/or abducens nerve enhancement had no evident eye movement palsy.

Conclusions: MRI cranial nerve enhancement is common in LNB patients, but it can be clinically occult. Facial and oculomotor nerves are most often affected. Enhancement of the facial nerve distal internal auditory canal and parotid segments correlate with degree of facial palsy.

Keywords: Central nervous system infections; Cranial nerves; Lyme neuroborreliosis; Magnetic resonance imaging; Vector borne diseases.

Fig. 1

Flow chart of sample and data selection for this cranial neuritis cohort study. Patients with newly diagnosed Lyme neuroborreliosis were invited to join a non-inferiority randomized clinical oral treatment trial and a longitudinal case–control study with MRI and neuropsychology markers in the same research project (BorrSci). Patients who received intravenous treatment were also invited in the MRI-neuropsychology study. Invitation was declined by 13 eligible patients

Fig. 2

Demonstration of no versus strong enhancement of the oculomotor nerves on 1 mm axial image reconstruction from 3D T1-weighted and fat-suppressed acquisition. The subject in (a) demonstrates no enhancement of oculomotor nerves (arrows), while subject in (b) shows bilateral strong enhancement (arrows)

Fig. 3

Evaluation of the facial nerve is complex due to a long course where some segments have physiological enhancement. Axial reconstruction from 3D T1-weighted and fat-suppressed acquisition shows no enhancement of the distal IAC segments (arrows in a), also there is no enhancement in the narrow labyrinthine segments that curve anterior toward the normal enhancing geniculate ganglions seen in the same axial slice. Axial images (b and c) are from a different subject at the level of the distal IAC and parotid gland, respectively. They demonstrate mild-moderate enhancement in the right distal IAC and strong enhancement in the left distal IAC (arrows in b), while no enhancement is seen in the right parotid segment (circle in c) and strong enhancement is present in the left parotid segment where the nerve is depicted as it curves anterior to approach the pes anserinus (arrow in c)

Fig. 4

Bar charts provide a graphical summary of the main study findings. The bars are number of nerves for each enhancement degree (right and left side for each subject, possible enhancement was considered as no enhancement), clustered by palsy or no palsy at baseline and follow up. Facial palsy is in the top row, and eye movement palsy in the bottom row

Fig. 5

Receiver operating characteristic curves for enhancement rate show that parotid enhancement is more specific, but less sensitive compared to distal IAC enhancement in predicting if facial palsy is present or not, both at baseline and after 6 months