Uncrossed epileptic seizures in Joubert syndrome

Abstract

Joubert syndrome and related disorders comprise a subgroup of ciliopathies defined by the presence of the 'molar tooth sign', a midbrain-hindbrain malformation identifiable by neuroimaging. Characteristically, the corticospinal tract and superior cerebellar peduncles do not decussate. Epileptic seizures are uncommon. We present a case of a 28-year-old man with a background of Leber's congenital amaurosis with nephronophthisis, requiring kidney transplantation, and mental retardation, who developed epileptic seizures consisting of a short muffled cry and involuntary shaking movements of the extremities beginning in the left upper limb; these episodes lasted several seconds and occurred in clusters. Simultaneous video-EEG recording showed an ictal pattern in the left frontal lobe. Brain MRI revealed the pathognomonic 'molar tooth sign'; diffusion tensor imaging (DTI)-tractography showed a lack of decussation of both corticospinal tracts. To the best of our knowledge, this is the first time that DTI-tractography has been used to uncover the anatomical substrate underlying the semiology of epileptic seizures.

Figure 1

(A) Sagittal MRI T1-weighted images through the cerebellum and brain stem of the patient, depicting the horizontalisation of the superior cerebellar peduncles and other hindbrain anomalies. (B) Note the ‘molar tooth sign’ on the axial plane.

Figure 2

EEG recording showing a diffused flattening followed by rhythmic delta activity in the left frontal area. Sensitivity 7 uV/mm, high frequency filter 70 Hz, low frequency filter 1 Hz, Notch 50 Hz, time base 30 mm/s. (B and C) Left frontal spike (*) shown in bipolar (B) and referential (C) montage.

Figure 3

(A) Diffusion tensor imaging (DTI)-tractography showing normal decussation of the corticospinal tract as a red dot between the cerebral pyramids (arrow). (B) DTI-tractography of our patient, showing the absence of decussation. Colours represent tract orientation in space; red, green and blue represent the x, y and z-axis, respectively. (C) DTI-tractography over T1-weighted sequential coronal planes of the brainstem, illustrating lack of decussation at the medullar pyramids.

Figure 4

Diffusion tensor imaging (DTI)-tractography reconstruction of the tracts showing the lack of decussation of the superior cerebellar peduncle.