Pearls & Oy-sters: Parietal Lobe Epilepsy in Disguise

Pearls

• Parietal lobe epilepsy (PLE) is characterized by frequent auras and diverse semiologies, largely due to the elaborate connections of the parietal lobe to other regions.

• Proprioceptive-induced seizures are a rare but unique expression of PLE. They are characterized by motor seizure attacks precipitated by proprioceptive stimuli of the extremities.

• Focal cortical dysplasia (FCD) is a common etiology of drug-refractory PLE. Bottom-of-sulcus dysplasia (BOSD) represents a distinctive subtype notable for its highly localized and subtle lesions, as well as an excellent surgical outcome.

Oy-sters

• PLE should be part of the differential in patients with paroxysmal movement disorders. Thorough history taking, especially of the triggers and motor attacks, is essential for a correct diagnosis.

• The presence of localized rhythmic epileptic discharges (REDs) on electroencephalography serves as an important indicator of the easily misdiagnosed FCD. A thorough history taking, careful review of MRI, and application of multimodal imaging postprocessing further facilitate subtle lesion detection.

• A transient response to antiseizure medications is common in FCD-associated epilepsy. However, early referral to surgery evaluation should be considered because drug refractoriness is likely to develop with time.

Case Report

A right-handed 10-year-old boy presented with recurrent movement-induced seizure attacks for several months. He described most of the episodes as a tingling sensation moving upward from the left foot to the left face, occurring over seconds. This was sometimes followed by dystonia of the left upper and lower extremities. The attacks were consistently provoked by walking, running, rubbing of his left foot, or simply by stepping onto an uneven ground. The patient and his parents were unaware of the family history with such attacks and declined genetic testing. Brain MRI and 24-hour EEG were negative. He was diagnosed with paroxysmal kinesigenic dyskinesia (PKD) and placed on carbamazepine and valproic acid at another medical institution. He remained relapse free for around 1 year but began experiencing focal to bilateral tonic-clonic seizures (FBTCSs) roughly twice a year. He also reported frequent movement/rubbing-induced focal seizures up to once per week. He was diagnosed with epilepsy.

Despite an optimal therapeutic dosing level, the patient recalled an increasing seizure frequency, with almost daily focal seizures and FBTCSs roughly once every 3 months. Thinking his disease was incurable, the patient discontinued all medications at age 36 years. Attack frequency increased significantly, with multiple focal seizures per day and FBTCSs up to once a week. The patient even became afraid of walking because it always led to falls. He came to our clinic and was admitted to the epilepsy unit for evaluation of surgical eligibility.

The patient underwent high-resolution MRI (eFigure 1, A–C, links.lww.com/WNL/B790) and interictal PET, both of which reported normal. Three days of video-EEG monitoring captured more than 20 episodes of focal seizures ranging from 10 to 30 seconds. Seizures were elicited or exacerbated by voluntary scratching of the left foot. Semiology consisted of auras presenting as sensory Jacksonian march on his left side, sometimes followed by tonic posturing of the left extremity. The patient was aware throughout the attack. On tapering of carbamazepine, 2 episodes of FBTCSs were captured, both of which were preceded by unconscious leg movements during sleep.

The awake and sleep EEG background were normal. On his interictal EEG, intermittent REDs were dominant in the right centroparietal region (P4, Pz, and Cz) (Figure 1A). During a habitual attack, more frequent REDs over the right centroparietal region were noted, corresponding to somatosensory auras. It was followed by right-sided focal fast epileptiform activity associated with tonic posturing of the left leg. FBTCSs were accompanied by focal fast activity in the right centroparietal region, followed by generalized spike and waves on EEG (Figure 1B).

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Figure 1 Electrical-Radiologic Features of the Patient With Proprioceptive-Induced Epilepsy Related With Bottom-of-Sulcus Dysplasia (BOSD) in the Superior Parietal Lobe

(A) Sample interictal EEG (time base 30 mm/sec, sensitivity 10 μV/mm) showed rhythmic epileptiform discharges (REDs, with arrows) over the right centroparietal region. (B) Ictal EEG (time base 30 mm/sec, sensitivity 10 μV/mm) showed RED with an increasing frequency, followed by fast epileptiform discharges over the right centroparietal region. The dashed line marked the seizure onset when the clinically observable epileptic symptoms (tonic posturing of the left leg) began. (C) Reexamination of the high-resolution MRI showed subtle cortical thickening maximal at the bottom of the postcentral sulcus. (D) Voxel-based morphometric MRI postprocessing further revealed abnormalities at the depth of the postcentral sulcus, part of the postcentral gyrus, and the superior parietal lobule.

Despite initial negative MRI reports, we still suspected abnormalities posterior to the central sulcus given the semiology and EEG findings. During the multidisciplinary presurgical conference, we reexamined the high-resolution MRI with a special attention to the postcentral area. Subtle cortical thickening maximal at the bottom of the sulcus was suspected (Figure 1C). Voxel-based MRI postprocessing further confirmed abnormality maximal at the bottom of the postcentral sulcus (Figure 1D). PET-MRI coregistration showed mild hypometabolism over the same area (eFigure 1D, links.lww.com/WNL/B790). Considering the lesion's proximity to eloquent areas (the sensorimotor cortex and the superior parietal lobule), intracranial electrode implantation was performed.

Stereoelectroencephalography recorded several of his habitual seizures, revealing an intralesional and perilesional ictal onset (Video 1). Near-total en bloc resection of the lesion, tailored with electrocorticography recording, was performed (eFigure 2, A–B, links.lww.com/WNL/B790). Tissue histopathology (eFigure 2, C–D) confirmed FCD type IIb, showing dysmorphic neurons and balloon cells along the gray-white matter junction, as well as mild dyslamination of cortical neurons. The diagnosis of bottom-of-sulcus dysplasia (BOSD) was given. After surgical resection, rubbing or movement of the left foot no longer induced seizure attacks. He was free of habitual seizures at the last follow-up (6 months postoperatively). No weakness or sensory loss was reported. He was maintained on a stable dose of carbamazepine and valproic acid after surgery.