Are there changes in intelligence and memory functioning following surgery for the treatment of refractory epilepsy in childhood?

MATERIALS AND METHODS: A retrospective review of the neuropsychological and medical variables of 26 children who underwent a cortical resection as part of the management of their medically refractory epilepsy was conducted. Neuropsychological variables included pre- and postoperative measures of intelligence (Wechsler Scales) and memory functioning (Wide Range Assessment of Memory and Learning). Medical variables included age at onset of seizures, age at surgery, site of resection, and degree of seizure control postoperatively. RESULTS: Twenty patients had temporal resections (13 left-sided). Six had extratemporal resections. In this series, cortical resection as treatment of epilepsy in children did not result in a significant change in performance on measures of intelligence or memory functioning. No significant correlation was found between the medical variables and the neuropsychological outcome.     

Surgical Indication for Refractory Childhood Epilepsy

Summary: Recent progress in surgical intervention for medically refractory epilepsy has helped to shed light on more complex epileptogenic problems in children and infants. Surgical treatment increasingly is being used in pediatric patients, but the indications for surgery in this age group have not been well defined. The developing child with a seizure disorder has several problems that are different from adults, such as neural plasticity, deleterious effects of seizures on developmental status, and spontaneous resolution of epilepsy. The critical age for irreversible brain dysfunction and the timing of surgery are the main issues for the treatment of children. Thus, earlier surgical intervention is generally recommended to prevent further deterimental seizure effects, but we still do not know the optimal age. Until the establishment of guidelines for pediatric epilepsy surgery, surgical indications should be determined by the prognosis and the presence of a resectable epileptogenic focus, which in turn are based on the localization of the epileptic focus, seizure frequency, severity, and cognitive function of each case, rather than just the patient's age.     

Predictors of outcome in pediatric epilepsy surgery

OBJECTIVE: To determine the correlation between pre- and perioperative variables on the outcome of children undergoing focal resections for medically intractable partial epilepsy. METHODS: Retrospective analysis of pre- and perioperative variables in a cohort of 75 patients younger than 12 years of age who underwent excisional surgery and had at least 1 year of follow-up. Outcome, measured by postoperative seizure frequency, was analyzed as a function of age at seizure onset, duration of epilepsy, presence of cognitive impairment, lobe of seizure origin, presence of a lesion, histopathology, and completeness of resection. Completeness of resection was defined on the basis of excising both the entire structural lesion if present and the region revealing prominent interictal and ictal abnormalities on intracranial EEG. RESULTS: Seventy-seven percent of patients had good outcomes (class 1 or 2), and 59% were seizure-free. Lesional status, site of resection, and pathologic diagnoses were not significant predictors of outcome except for in multilobar resection, for which overall outcome was relatively poor (44% class 3 or 4; 22% seizure-free). Completeness of resection was the only significant predictor of good outcome (p < 0.001), with 92% of patients who underwent complete resection of the epileptogenic zone achieving good outcome compared with 50% of patients who had incomplete resections. CONCLUSION: In this series of pediatric patients, complete resection of the lesion and the electrographically abnormal region was the main determinant of outcome after focal resections. Except for multilobar resections, other factors examined in this study did not significantly influence postoperative seizure prognosis and should not influence candidate selection for the surgical process.     

Temporal patterns and mechanisms of epilepsy surgery failure

Epilepsy surgery is an accepted treatment option in patients with medically refractory focal epilepsy. Despite various advances in recording and localization noninvasive and invasive techniques (including electroencephalography (EEG), magnetic resonance imaging (MRI), positron emission tomography (PET), single photon emission computed tomography (SPECT), magnetoencephalography (MEG), subdural grids, depth electrodes, and so on), the seizure outcome following surgical resection remains suboptimal in a significant number of patients. The availability of long‐term outcome data on an increasing number of patients suggests two major temporal patterns of seizure recurrence (early vs. late) that implicate the following two different mechanisms for seizure recurrence: (1) a failure to either define/resect the epileptogenic zone, and (2) the nonstatic nature of epilepsy as a disease through the persistence of proepileptic cortical pathology. We describe the temporal patterns of epilepsy surgery failures and discuss their potential clinical, histopathologic, genetic, and molecular mechanisms. In addition, we review predictors of successful surgical interventions and analyze the natural history of epilepsy following surgical intervention. We hypothesize that the acute/early postoperative failures are due to errors in localizing and/or resecting the epileptic focus, whereas late recurrences are likely due to development/maturation of a new and active epileptic focus (de novo epileptogenesis).     

儿童难治性癫痫的外科治疗

目的 分析儿童难治性癫痫的病因、外科手术的适应证和预后.方法 回顾性分析采用外科手术治疗342例儿童癫痫的经验.结果 皮质发育障碍是本组儿童难治性癫痫的最重要病因,占18.4%.药物难治性癫痫综合征占13.5%.术后疗效Engel Ⅰ级158例,Ⅱ级76例,Ⅲ级61例,Ⅳ级47例.平均智商(1Q)从术前的69.2分提高到79.8分.术前显示智力低下者术后亦有明显改善.结论 早期外科干预能有效地控制癫痫发作、改善智力损害,智力低下不应是外科治疗的禁忌证.同时,正确认识儿童难治性癫痫的病凶和病理埘儿童癫痫的外科治疗具有重要作用.     

Long-term outcome of nonsurgical candidates with medically refractory localization-related epilepsy

PURPOSE: Epilepsy surgery can result in complete seizure remission rates of upto 80% in patients with mesial temporal sclerosis and unilateral seizures. The seizure-free rate after surgery for patients with extratemporal nonlesional epilepsy has ranged between 30% and 40%. Some patients with medically refractory localization-related epilepsy cannot be offered surgical resection because of inadequate localization of the epileptogenic zone, documentation of bilateral ictal onsets, or functionally important areas of cortex that prohibit resection. The short-term rate of complete remission with medications in temporal lobe epilepsy is poor. Less is known about remission rates in patients who are not surgical candidates. In this study, we evaluated the outcome of medical treatment in patients with medically refractory partial epilepsy who were evaluated for possible epilepsy surgery but deemed to be inadequate surgical candidates. METHODS: A retrospective chart review and telephone survey with a self-rating questionnaire were completed for all patients who underwent epilepsy surgery evaluation but were not ultimately offered surgical treatment at the University of Michigan from 1990 through 1998. We assessed changes in seizure frequency and type, imaging characteristics, ictal recordings, interim medication history, and subjective changes in quality of life. RESULTS: Thirty-four subjects were available for follow-up study, at an average of >4 years after surgical evaluation. A significant reduction in seizure frequency was noted at the time of follow-up compared with that at the time of surgical evaluation. Of patients, 21% achieved seizure remission and remained seizure free for an average of 2.5 years. Four of the seven seizure-free patients attributed their remission to new antiepileptic drugs (AEDs). On a global self-rating item, 15 of 34, or 44%, felt more or much more satisfied with their lives, and 41% felt their quality of life was stable. CONCLUSIONS: A surprisingly large number of patients we surveyed, with refractory partial epilepsy not eligible for surgical management, reported reduced seizure frequency at follow-up, and 21% were seizure free. Our findings suggest that the long-term prognosis in patients with refractory partial epilepsy who are not surgical candidates may be more positive than might be generally expected.     

Surgery for focal epilepsy in the older patient

Eight of the 237 patients who received a surgical procedure for intractable partial epilepsy at the Mayo Clinic during a 3-year period were 50 years of age or older. All patients had disabling partial seizures of several years in duration that were refractory to antiepileptic drug medication. A neuroimaging-identified epileptogenic lesion prompted referral for surgical treatment in three patients. The only clinically significant morbidity associated with surgery in the eight patients was a transient exacerbation of an aphasia in a patient who underwent a left frontal corticectomy. All eight patients had a favorable seizure outcome, and three patients postoperatively are seizure free. Epilepsy surgery may be an appropriate alternate therapy for select patients in the sixth decade of life or older with medically refractory partial seizures.     

Tuberous Sclerosis and Multiple Tubers: Localizing the Epileptogenic Zone

Summary:  Tuberous sclerosis complex (TSC) is associated with medically refractory seizures and developmental delay in children. These epilepsies are often resistant to antiepileptic drugs (AEDs), may be quite severe, and usually have a negative impact on the child's neurological and cognitive development. It is believed that functional outcome is improved if seizures can be controlled at an early age. The surgical treatment of intractable epilepsy in children and adults with TSC has gained significant interest in recent years. Previously published studies have shown a potential benefit from resection of single tubers, with most of the results noted in relatively older children. All of these reports support the idea that if a single primary epileptogenic tuber/region can be identified, then a surgical approach is appropriate. However, most children with TSC have multiple potentially epileptogenic tubers, rendering localization challenging, and they are therefore rejected as possible surgical candidates. We have utilized a novel surgical approach using invasive intracranial monitoring, which is typically multistaged and bilateral. Here we present an illustrative case of a young boy with TSC and medically refractory epilepsy who underwent a staged surgical approach. This multistage surgical approach has been useful in identifying both primary and secondary epileptogenic zones in TSC patients with multiple tubers. Multiple or bilateral seizure foci are not necessarily a contraindication to surgery in selected TSC patients. Long-term follow-up will determine whether this approach has durable effects. We await better methods for identifying the epileptogenic zone, both noninvasive and invasive.     

Tailored cortical resection following image guided subdural grid implantation for medically refractory epilepsy

The aim of this study was to report the safety and efficacy of tailored cortical resection based on image guided subdural electrode implantations in eight patients with medically refractory epilepsy. The patients were selected for multimodality image guided subdural grid implantation, inpatient invasive electroencephalography video monitoring and surgical resection of epileptogenic foci. All patients had frequent disabling, medically refractory seizures pre-operatively. At a minimum of 10 months post-resection all patients had a worthwhile improvement in seizure frequency, with 7 of the 8 (87.5%) having an excellent outcome (Engel Class I). Short-term complications of grid implantation were: one patient with a post-operative subdural haemorrhage and one patient with a transient fluctuating dysphasia. The only long-term complication was a mild, non-disabling dysarthria following resection near eloquent speech cortex in one patient. We conclude that tailored cortical resection following image-guided insertion of subdural grids is a reliable, safe and highly effective method for the treatment of medically refractory epilepsy in carefully selected patients.     

Surgical Outcome in Patients with Epilepsy with Occult Vascular Malformations Treated with Lesionectomy

Summary: Purpose: This retrospective study reports the long-term surgical outcome of patients with medically refractory epilepsy and vascular malformations who were treated with lesionectomy. A detailed analysis of surgical failures had been performed in an attempt to define predictors of surgical success and failure.
Methods: Fifteen patients with medically intractable epilepsy and angiographically occult vascular malformations (AOVMs) were treated surgically with lesionectomy at Duke University Medical Center. Lesionectomy consisted of removal of the AOVM and surrounding hemosiderin-stained brain only, without the use of electrocorticography (ECoG) to guide resection.
Results: Eleven (73%) patients are seizure free after lesionectomy. Three showed no significant improvement, and one patient died, presumably after a seizure. Age of onset, duration of seizures, age at resection, and gender did not affect outcome. All patients with neocortical AOVMs in whom EEG findings correlated with the site of the lesion were seizure free after lesional resection. Treatment failures were associated with the presence of multiple intracranial lesions, poorly localized or diffuse EEG findings, discordant positron emission tomography (PET) imaging, or with a lesion in close proximity to the limbic system.
Conclusions: Lesionectomy, with removal of surrounding hemosiderin-stained brain, can be considered the procedure of choice in carefully selected patients with epilepsy with occult vascular malformations.     

Predictors of seizure outcome in newly diagnosed partial epilepsy: memory performance as a prognostic factor.

The epilepsy patients whose seizures will prove to be refractory should be identified as early as possible, and thus the need for new prognostic factors of intractable epilepsy is evident. The aim of the study was to investigate predictors of seizure outcome in a multivariate analysis. Neurological, electroencephalography (EEG) and neuropsychological variables were analyzed as potential predictors of epilepsy. Eighty-nine newly diagnosed adult patients with partial epilepsy were, after a prospective 2-year follow-up period, categorized into one of the two groups: patients with satisfactorily controlled epilepsy, and patients with refractory epilepsy. Six variables predicted 2-year seizure outcome: presence of spike focus in EEG, partial complex or mixed seizure type, remote symptomatic etiology, moderately impaired memory performance in immediate recall and in delayed recognition of the word list, and age at the time of diagnosis. The correct seizure outcome could be predicted with the model in 94% of newly diagnosed epilepsy patients. The presence of verbal memory impairment at the time of the diagnosis of partial epilepsy is a significant predictor of seizure outcome and, together with clinical and EEG variables, it predicts seizure outcome in the majority of the patients. Memory performance as a prognostic factor is of most value in patients with risk of refractory epilepsy and when used in a multidisciplinary setting.     

Stereoelectroencephalography in the “difficult to localize” refractory focal epilepsy: Early experience from a North American epilepsy center

Purpose: Stereo‐electroencephalography (SEEG) enables precise recordings from deep cortical structures, multiple noncontiguous lobes, as well as bilateral explorations while avoiding large craniotomies. Despite a long reported successful record, its application in the United States has not been widely adopted. We report on our initial experience with the SEEG methodology in the extraoperative mapping of refractory focal epilepsy in patients who were not considered optimal surgical candidates for other methods of invasive monitoring. We focused on the applied surgical technique and its utility and efficacy in this subgroup of patients. Methods: Between March 2009 and May 2011, 100 patients with the diagnosis of medically refractory focal epilepsy who were not considered optimal candidates for subdural grids and strips placement underwent SEEG implantation at Cleveland Clinic Epilepsy Center. Demographics, noninvasive clinical data, number and location of implanted electrodes, electrophysiologic localization of the epileptic zone, complications, and short‐term seizure outcome after resection were prospectively collected and analyzed. Key Findings: Mean age was 32 years (range 5–68 years); 54 were male and 46 female. The mean follow‐up after resection was 15 months. In total, 1,310 electrodes were implanted. Analyses of the SEEG recordings resulted in the electrographic localization of the epileptogenic focus in 96 patients. In the group of 75 patients who underwent resection, only 53 had at least 12 months follow‐up. From this group, 33 patients (62.3%) were seizure‐free at the end of the follow‐up period. The presence of abnormal pathologic finding was strongly associated with postoperative seizure control (p = 0.005). The risk of hemorrhagic complications per electrode was 0.2%. Significance: In patients who are not considered to be ideal candidates for subdural grids and strips implantation, the SEEG methodology is a safe, useful and reliable alternative option for invasive monitoring in patients with refractory focal epilepsy, providing an additional mean for seizure localization and control in a “difficult to localize” subgroup of patients.     

Subdural strip electrode monitoring and surgical decision making in refractory epilepsy: validity and prognostic value of noninvasive localizing data

We analyzed the rationale for invasive monitoring in refractory epilepsy. In 54 selected patients, video/scalp-EEG was insufficient for seizure focus localization. Therefore, bilateral subdural electrodes were implanted for ictal recording. In 40 (74.1%) of 54 patients, ictal electrocorticography (ECoG) localized a seizure focus amenable to resection. Fourteen (25.9%) of 54 patients, had multiple foci or primary generalized seizures. Among 36 patients who had focal resection with at least 1-year follow-up, 32 (88.9%) are either seizure-free or significantly improved. Magnetic resonance imaging (MRI) and interictal single photon emission computed tomography (SPECT) had the highest sensitivity and specificity (80.0 and 81.8%, respectively) and the greatest diagnostic value (64.0 and 77.8%, respectively) for seizure focus localization. Independent of electrophysiologic data, MRI determination of focal abnormality was prognostic for seizure-free outcome. Concordance of one or more noninvasive techniques with ictal ECoG seizure focus localization was statistically significant in predicting seizure-free outcome. Although interest in noninvasive selection of candidates for focal resection is increasing, there remains a role for invasive monitoring of epileptogenic foci that are difficult to localize. Our study should improve selection of patients with refractory epilepsy for focal resection when ictal ECoG is used in conjunction with noninvasive data for surgical decision making.     

小儿顽固性癫痫的外科治疗

目的回顾性分析2002年6月至2007年6月间,在我院接受手术治疗的142例儿童顽固性癫痫患者的手术经验。方法术前评估和术中脑电检查显示为局灶性改变者行致痫灶切除或脑叶切除和（或）多软膜下横纤维切断（MST）。检查提示一侧半球为主多灶性改变者,术中行多脑叶切除联合MST和/或胼胝体部分切开。结果本组随访1～5年,平均3年。142例中有65例获得I级（Engel分级）,34例获得Ⅱ级,25例为Ⅲ级预后。有效率87.3%,效果优良率为69.7%。平均总智商（FIQ）从术前的65.4分提高到80.9分,癫痫病程和术前药物难治的时间越短,智商改善越明显。本组有16例出现暂时性的并发症,无手术死亡。结论对小儿顽固性癫痫患者,只要病例选择适当,手术方式合理,其手术效果是令人满意的,对这类患儿的早期外科干预,不仅可以有效地控制癫痫发作,而且可改善已有的智力损害和减少生活残疾。     

Surgical treatment for epilepsy

Nearly one-third of patients with newly diagnosed epilepsy will develop medically refractory seizure disorders. The initial response to antiepileptic drug therapy is highly predictive of long-term outcome. Patients with intractable epilepsy may have a progressive disorder that is medically, physically, and socially disabling. Surgical resection of the epileptogenic zone or lesional pathology, or both, may significantly reduce seizure tendency in selected patients. The present review supports the position that early and effective epilepsy surgery may not only render the patient with intractable partial epilepsy seizure-free, but also allow the individual to become a participating and productive member of society. Patients with surgically remediable epileptic syndromes should be identified early in the evaluation and treatment of their seizure disorders. Favorable candidates for focal cortical resection include individuals with medial temporal lobe epilepsy and partial seizures related to selected lesional pathology, e.g. primary brain tumor or vascular anomalies. In conclusion, surgical treatment of intractable partial epilepsy has been shown to compare favorably to antiepileptic drug therapy. Individuals rendered seizure-free may experience a significant improvement in quality of life. Patients who fail to respond to initial antiepileptic drug therapy should be “triaged” to a presurgical evaluation. Ictal semiology combined with structural magnetic resonance imaging and the electroclinical correlation may permit identification of candidates for early and effective surgical treatment.     

Surgical management of pediatric tumor-associated epilepsy

Brain tumors are a common cause of seizures in children. Early surgical treatment can improve seizure outcome, but controversy exists regarding the most appropriate type of surgical intervention. Some studies suggest tumor resection alone is sufficient, while others recommend mapping and resection of the surrounding epileptogenic foci to optimize seizure outcome. To address this issue, we reviewed the charts of 34 pediatric patients aged 18 months to 20 years with medically intractable epilepsy and primary brain tumors. The average age at operation was 12.6 years, and patients had seizures for an average of 6.4 years. The majority of tumors were located in the temporal lobe. Seventeen patients, because of tumor location near an eloquent area, underwent extraoperative mapping using subdural electrode grids prior to definitive tumor resection. Fourteen of these patients had a gross total tumor resection, yet only two had a distinct zone of ictal onset identified and resected. The remaining 17 patients had tumors either in the nondominant hemisphere or far removed from speech-sensitive areas, and therefore did not undergo extraoperative subdural electroencephalograph mapping. Fourteen of these patients also had a gross total tumor resection, while none had intraoperative electrocorticography to guide the resection of additional nontumoral tissue. Overall, of the 28 patients treated with a gross total tumor resection, 24 (86%) are seizure free, while the other four are significantly improved. Of the six patients who had a subtotal tumor removal, five have persistent seizures. The mean follow-up was 3.6 years. We conclude that in children and adolescents, completeness of tumor resection is the most important factor in determining seizure outcome. The routine mapping and resection of epileptogenic foci might not be necessary in the majority of patients. As a corollary, the use of subdural electrode grids in pediatric patients with tumor-associated epilepsy should be limited to cases requiring extraoperative cortical stimulation for localization of nearby eloquent cortex.     

Epilepsy with dual pathology: Surgical treatment of cortical dysplasia accompanied by hippocampal sclerosis

Purpose: The presence of two or more epileptogenic pathologies in patients with epilepsy is often observed, and the coexistence of focal cortical dysplasia (FCD) with hippocampal sclerosis (HS) is one of the most frequent clinical presentations. Although surgical resection has been an important treatment for patients with refractory epilepsy associated with FCD, there are few studies on the surgical treatment of FCD accompanied by HS, and treatment by resection of both neocortical dysplastic tissue and hippocampus is still controversial. Methods: We retrospectively recruited epilepsy patients who had undergone surgical treatment for refractory epilepsy with the pathologic diagnosis of FCD and the radiologic evidence of HS. We evaluated the prognostic roles of clinical factors, various diagnostic modalities, surgical procedures, and the severity of pathology. Results: A total of 40 patients were included, and only 35.0% of patients became seizure free. Complete resection of the epileptogenic area (p = 0.02), and the presence of dysmorphic neurons or balloon cells on histopathology (p = 0.01) were associated with favorable surgical outcomes. Patients who underwent hippocampal resection were more likely to have a favorable surgical outcome (p = 0.02). Conclusions: We show that patients with complete resection of epileptogenic area, the presence of dysmorphic neurons or balloon cells on histopathology, or resection of hippocampus have a higher chance of a favorable surgical outcome. We believe that this observation is useful in planning of surgical procedures and predicting the prognoses of individual patients with FCD patients accompanied by HS.     

伴顽固性癫痫的脑肿瘤的病理分析

目的 分析伴顽固性癫痫患者的脑肿瘤病理特点,探讨最适合的手术方式.方法 在符合顽固性癫痫并进行手术治疗的病例中,回顾分析45例病理证实存在脑肿瘤的病例资料.结果 癫痫灶位于额叶8例,颞叶34例,顶枕叶3例;病理证实神经元和混合性神经元-胶质肿瘤35例(78%).WHO Ⅰ级36例,WHO Ⅰ～Ⅱ4例,WHO Ⅱ级5例.术后随访1年以上的42例,全部生存.癫痫发作控制结果 显示Engel Ⅰ级32例(76%),Ⅱ级5例,Ⅲ级4例,Ⅳ级1例.结论 与顽固性癫痫相关的脑肿瘤是一类特殊的病理组群,手术切除包括肿瘤在内的癫痫灶,效果满意.     

Epilepsy Surgery in the First Three Years of Life

Summary: Purpose: Partial seizures in early postnatal life may be catastrophic and associated with poor long-term outcome. Epilepsy surgery can alleviate partial seizures in older children and adults, but there is little experience with surgical therapy in infancy apart from hemispheric epilepsy syndromes.
Methods: We analyzed the results of cortical resection to treat medically refractory partial epilepsy in 31 children (16 boys, 15 girls) aged <3 years (mean, 18.3 months). Subjects were included only if seizure relief was the primary indication for surgery.
Results: Follow-up of at least 1 year (mean, 4.6 years) in 26 patients revealed that 16 were seizure-free, 4 had >90% seizure reduction, and 6 had <90% reduction. There was no significant difference in seizure outcome between hemispherectomy/multilobar resections and lobar resections or temporal versus extratemporal resection. Seizure outcome was independent of the amount of cortex removed in nonlesional patients. Only the presence of a discrete lesion on preoperative neuroimaging correlated with a favorable outcome. Family perceptions of accelerated development in seizure-free patients were not confirmed on developmental assessment.
Conclusions: We conclude that cortical resection often benefits very young children with catastrophic partial seizures, but does not guarantee enhanced neurological development. The location and extent of the excised cortex may not be critical as long as the entire epileptogenic region and tesion are removed.     

Foramen ovale electrodes in the preoperative evaluation of temporal lobe epilepsy in children

Purpose:  Foramen ovale electrodes (FOEs) can localize the epileptogenic zone in adults with mesial temporal lobe epilepsy (TLE). Our aim was to investigate the feasibility and safety of using FOEs to investigate refractory TLE in children.
Methods:  Thirty-eight children with seizure semiology and video-EEG (electroencephalography) consistent with medically refractory TLE, and/or the presence of a lesion in the temporal lobe, had FOEs inserted. Complications occurring during the monitoring and up to 3 months after surgery and the long-term seizure outcome were registered.
Results:  Forty electrodes were placed in 38 patients. The mean age of the patients was 9.8 years (range 2.3–15.4 years). FOEs confirmed a unilateral mesial temporal lobe seizure onset in 14 patients, onset in both FOEs and lateral electrodes in two patients, and onset in the anterior temporal electrodes in only one patient. Six patients had seizures recorded but were not considered surgical candidates; four patients had no seizures recorded, and 11 patients were further investigated with depth electrodes. One patient (2.6%) developed a hematoma in the cheek, and in two patients the electrodes were extracranial but could still be used for recording. Twenty-eight children had a temporal resection; 25 were Engel class I at follow-up.
Discussion:  FOEs are safe to use in children and provide valuable information on the mesial temporal lobe structures in the preoperative investigation of pediatric TLE. Patient selection for FOE investigation is, however, essential for a conclusive result.