Ictal SPECT in Nonlesional Extratemporal Epilepsy

Authors


  • Presented in part at the 57th Annual Meeting of the American Epilepsy Society in Boston, Massachusetts, U.S.A.

Address correspondence and reprint requests to Dr. G.D. Cascino at 200 First St., S.W., Rochester, MN 55905, U.S.A. E-mail: gcascino@mayo.edu

Abstract

Summary: Purpose: Ictal single-photon emission computed tomography (SPECT) may be a reliable indicator of the ictal onset zone in patients with intractable partial epilepsy who are being considered for epilepsy surgery. The rationale for the illustrated case report is to evaluate the use of an innovation in SPECT imaging in a patient with nonlesional extratemporal epilepsy.

Methods: We investigated the presurgical evaluation and operative outcome in a patient with intractable partial epilepsy. The ictal semiology indicated a “hypermotor” seizure with bipedal automatism. The electroclinical correlation and magnetic resonance imaging (MRI) did not suggest the appropriate localization of the epileptogenic zone. A subtraction periictal SPECT coregistered to MRI (SISCOM) was peformed.

Results: SISCOM revealed a region of localized hyperperfusion in the right supplementary sensorimotor area. Chronic intracranial EEG monitoring confirmed the relationship between the localized SISCOM alteration and the ictal onset zone. The patient was rendered seizure free after surgical treatment.

Conclusions: SISCOM may be used to identify potential candidates for surgical treatment of nonlesional extratemporal epilepsy. Periictal imaging may also alter the strategy for intracranial EEG recordings and focal cortical resection.

MAYO CLINIC SISCOM PROTOCOL

Subtraction periictal single-photon emission computed tomography (SPECT) coregistered to magnetic resonance imaging (MRI) (SISCOM) is performed in selected patients being considered for surgical treatment (1–9). The current protocol at the Mayo Clinic in Rochester, Minnesota, requires an MRI head seizure protocol and routine EEG before admission to the epilepsy-monitoring unit (1–3). Review of the outpatient evaluation and the initial video-EEG findings will be used to determine the potential candidates for a SISCOM study. The periictal neuroimaging studies are performed from 7 a.m. to 11 p.m. on 7 days of the week. The radioligand technetium-99m ethyl cysteinate diethylester (99mTc-ECD) is injected as soon after seizure onset as possible (1–4,6). The interictal injection and scan are performed 24 h or later after the ictal imaging study. Patients are treated with antiepileptic drug medication (including benzodiazepine therapy if necessary) to suppress seizure activity during the period between the two injections. Individuals undergo continuous EEG monitoring at the time of the ictal and interictal SPECT injections (9). If appropriate, the patients receive sedation at the of the neuroimaging studies. A nurse accompanies the patient to nuclear medicine. The patients ultimately are discussed at a surgical epilepsy conference, at which time the comprehensive presurgical evaluation is reviewed. Selected candidates may proceed with prolonged intracranial EEG recordings or epilepsy surgery, or both. Neuropsychometry, visual perimetry, and cerebral arteriography with a sodium amobarbital study are performed before surgical treatment.

ILLUSTRATED CASE REPORT

A 13-year-old patient was initially seen with a medically refractory seizure disorder. The patient had one seizure type of clinical event associated with “discomfort” in his feet followed by blinking of the right eye, bicycling movements in his legs, and posturing in both upper extremities, maximal left. The seizures typically emerged from sleep and were associated with apparent altered awareness. The age at seizure onset was ∼4 years. No history of remote symptomatic neurologic disease was reported. The neurologic examination was normal. Interictal EEG showed midline spike discharges (Cz) during sleep (Fig. 1). Quantitative head MRI was normal. The scalp-recorded ictal EEG revealed a subtle midline and bilateral central region seizure pattern without definite lateralization (Fig. 2). The ictal behavior included “hypermotor” activity and prominent bipedal automatism with flexion of the right upper extremity and extension of the left upper extremity. The SISCOM study showed a region of focal hyperperfusion in the mesial aspect of the right cerebral hemisphere (Fig. 3). Long-term intracranial EEG monitoring was performed with the electrodes placed over the SISCOM abnormality. A focal cortical resection was performed. The pathological findings confirmed the presence of focal cortical dysplasia. The patient has remained seizure free after surgery.

Figure 1.

Midline interictal spike discharges.

Figure 2.

Ictal EEG pattern during typical clinical seizure.

Figure 3.

Subtracted periictal single-photon emission computed tomography (SPECT) coregistered to structural magnetic resonance imaging (MRI; SISCOM) in a patient with right supplementary sensorimotor area seizures. MRI study was normal. Ictal SPECT and interictal SPECT did not reveal a definite perfusion abnormality. A SPECT subtraction study showed a focal cerebral hyperperfusion alteration in the right central region. The SISCOM study indicated the anatomic localization of the periictal focal hyperperfusion abnormality. (Note: the right cerebral hemisphere is on the left side of the figures.)

This patient has a symptomatic partial epilepsy of probable right supplementary sensorimotor area origin. The SISCOM was used to detect the seizure-onset zone. The concordance of the SISCOM and intracranial EEG findings indicated that the patient was a favorable operative candidate. The patient had supplementary sensorimotor seizures. The diagnostic yield and prognostic importance of SISCOM in patients with nonlesional extratemporal epilepsy has previously been presented (7).

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