Neuron-Specific Enolase as a Biomarker in Ifosfamide-Induced Encephalopathy: A Case Report.

Although ifosfamide-derived encephalopathy is generally favorable and clinically monitored, this case study suggests that NSE, in the context of ifosfamide-induced encephalopathy, may be an interesting companion biomarker for monitoring outcomes.

We report here a case study of a woman who experienced ifosfamide-induced encephalopathy with clinical recovery consistent with improved EEG toxic patterns and decreased NSE levels in peripheral blood. These results are consistent with the literature on the use of NSE in encephalopathies, regardless of the underlying etiology. NSE is a specific biomarker for neurons for which increases correlate with a wide range of conditions, including severe head trauma, stroke, central nervous system infections, neurodegenerative diseases, certain tumor pathologies such as blastogenic or neuroendocrine tumors, as well as metabolic and toxic encephalopathies [ 4 ]. The half-life of NSE in peripheral blood is estimated at around 24 h, and a recent review examines the pathophysiological mechanisms behind the increase in NSE in brain injuries. These mechanisms include increased permeability of the neuron membrane and blood-brain barrier under cellular stress. NSE holds its neuronal specificity in relation to its involvement in neuronal glycolysis. Under neuronal stress, a rapid increase in NSE synthesis plays a neuroprotective role through pyruvate kinase, which converts NSE to ATP and ameliorates hypoxia in response to damage [ 8 ]. There is a strong rationale for the use of companion biomarkers in clinical encephalopathies, regardless of the underlying etiology. A meta-analysis showed a strong association between elevated NSE levels and a higher risk of sepsis-associated encephalopathy and mortality in septic patients [ 9 ]. NSE also has a predictive value in children with acute nontraumatic encephalopathies [ 10 ]. In experimentally induced endotoxemia, NSE levels were also correlated with clinical improvement in working memory and psychomotor speed capacity [ 11 ]. NSE levels are also known to have prognostic value and are correlated with EEG patterns and neuroradiography findings in newborns [ 12 ]. There is no consensus on the definition of a universal interpretation threshold for the NSE assay or in cases of encephalopathy. We have limited exploitable data in our institute, but we would like to use this assay (which is easy and fast) to overcome difficult availability of EEG. We conduct the NSE assay as soon as the first neurological or behavioral symptoms emerge, simultaneously scheduling the EEG. We aim to repeat the analysis before each EEG to monitor NSE levels, EEG features, and the clinical condition. In this case study, decrease of NSE level was associated with clinical recovery of ifosfamide-induced encephalopathy and normalization of EEG features. A retrospective analysis of the EEGs of 16 patients with ifosfamide-induced encephalopathy revealed characteristic features such as the presence of generalized periodic discharges with or without triphasic morphology in 9 patients, background slowing and intermittent rhythmic delta activity in 4 patients, and bursts of bilateral synchronized delta activity in 2 patients. For other abnormalities including global slowing of background activity, with a predominant shift into theta and delta bands, 1 patient experimented a nonconvulsive status epilepticus and 6 patients had abnormal orofacial movements. All 16 patients experienced disorientation, delirium, or inattention; 13 patients had somnolence or lethargy; 4 patients had aphasia or mutism; 1 patient had generalized tonic-clonic seizures; 1 patient had hallucinations; gait disorders were identified in 2 patients [ 13 ]. This case study found EEG features in line with the abnormalities reported in this series of ifosfamide-related encephalopathy cases, such as bilateral slow delta activity and the presence of generalized periodic discharges with triphasic morphology without additional features. Clinical findings in this case study were also consistent with reported symptoms of this article. A recent detailed review explored the pathways of ifosfamide-induced encephalopathy through the analysis of 61 plasma samples from patients who had experienced this side effect. The initial hypothesis proposed is the presence of numerous endogenous or drug-related metabolites with the property of disrupting synapses and neuronal signaling. These include 5 main metabolites contributing to a “perfect storm” including 2-chloroacetaldehyde, a metabolic product of the N-dechloroethylation of ifosfamide, which inhibits mitochondrial fatty acid oxidation and oxidative phosphorylation; CAA, which inhibits gluconeogenesis in astrocytes; S-carboxymethyl- l -cysteine, an inert metabolite of ifosfamide that could induce cellular acidification, a possible biological mechanism for the development of ifosfamide-induced encephalopathy; acrolein a metabolite known for genotoxicity to mitochondrial DNA; and 3-HPA, which inhibits GABA transaminase. A metabolic profile emerges, with the proportion of different metabolites depending on the occurrence of ifosfamide-induced encephalopathy. In addition to the identification of alternative metabolites (such as 3-phosphoserine or ceramides), the role of oxidative stress in glutathione synthesis may play a role in this clinical entity [ 14 ]. Ifosfamide-induced encephalopathy is a severe and debilitating condition, likely representing one end of a spectrum. Subclinical forms, such as mild confusion and behavioral changes, are not uncommon and often go unreported by patients, or not identified by clinicians. A valuable investigation could involve monitoring serial NSE levels in all patients receiving ifosfamide. This approach could help characterize the typical changes throughout treatment and, more importantly, allow clinicians to predict the onset of encephalopathy, enabling early intervention (e.g., hydration or methylene blue administration) before symptoms become severe. Currently, no data are available regarding chemotherapy-induced encephalopathy and NSE assay. The decrease in NSE levels was correlated in this case study with the improvement in EEG, suggesting a possible relationship in this clinical setting. These findings complement the existing literature on the use of NSE in encephalopathies, providing an opportunity to identify companion biomarkers for ifosfamide-induced encephalopathy.

Ifosfamide is a bifunctional alkylating agent that acts via direct interaction with DNA and is mainly used in the treatment of sarcoma, ovarian or breast cancer, and certain lymphoid diseases. Ifosfamide is a prodrug that is converted into active metabolites through cytochrome P450, mainly catalyzed by the isoform CYP3A4. This leads to the production of multiple neurotoxic drug-related metabolites like chloroacetaldehyde (CAA), which can cause encephalopathies [ 1 ]. The pathophysiology of this condition is complex and multifactorial. Risk factors for the development of ifosfamide encephalopathy include age over 60, female gender, cisplatin administration, hypoalbuminemia, and suspected causes include ifosfamide dose ≥2,000 mg/m 2 /day and the sarcomatous nature of the tumor [ 2 ]. The clinical symptoms vary, ranging from simple confusion, cerebral ataxia, and visual hallucinations to coma. As soon as the symptoms reach grade II, current treatment should be immediately suspended. Appropriate hydration must be initiated to facilitate the metabolite elimination. The efficacy of methylene blue administration remains uncertain and is based on a few retrospective and case reports. Methylene blue is thought to inhibit the enzymes involved in CAA formation [ 3 ]. The symptoms of ifosfamide encephalopathy are nonspecific and can be caused by other conditions prevalent in this population. These conditions include reactions to other medications and sepsis. To date, no biomarkers have been evaluated in this setting. Neuron-specific enolase (NSE) is a well-established neuronal biomarker associated with elevated peripheral blood levels in a variety of pathological conditions involving the central nervous system [ 4 ]. This is why we perform this biomarker assay as soon as neurological or behavioral symptoms appear, as the diagnosis of this ifosfamide encephalopathy is sometimes difficult to establish and delayed. Here, we present a case report of a woman who experienced ifosfamide-induced encephalopathy with favorable clinical outcomes and an improvement in NSE levels, as well as normalization of electroencephalogram (EEG) patterns under methylene blue treatment. We believe that the use of NSE in this setting can help discriminate ifosfamide encephalopathy from other complications.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

The authors declare that no financial support was received for the research, authorship, and/or publication of this article.

A 58-year-old woman with a history of obstructive sleep apnea syndrome and endometriosis surgery complained of progressive difficulty in mobilization, persistent left hip pain, and sleep impairment. Several months later, high-grade osteosarcoma was identified as a pathological fracture. A multidisciplinary decision proposed primary surgery in view of need to remain in bed due to functional impotence, with adjuvant chemotherapy. One month later, the patient underwent proximal femoral resection associated with reconstruction using an MATRAS prosthesis, with favorable postoperative results, allowing progressive mobilization. The first cycle of chemotherapy according to the API/AI protocol was administered with doxorubicin 20 mg/m 2 on day 1, cisplatin 100 mg/m 2 on day 1, and ifosfamide 3,000 mg/m 2 on days 1 to 3 [ 5 ]. The following morning on day 4, the patient presented with mild fatigue, nausea without vomiting, and temporospatial worsening confusion. Aphasia and somnolence were succeeded by a rapid intensification of symptoms, with the onset of marked psychomotor agitation, persecutory delirium with a background of anxiety, and insomnia. Mild orofacial dyskinesias were observed concomitantly with psychomotor agitation and aggressive behavior. The patient also presented episodes of stooling in inappropriate places on days 4 and 5. The combination of symptoms and post-chemotherapy time frame prompted early suspicion of grade 3 ifosfamide-induced encephalopathy according to the Common Terminology Criteria for Adverse Events (CTCAE) V5.0 [ 6 ]. Emergency blood ionograms, liver function tests, blood gases, and cerebral CT scan were normal. EEG on day 4 showed a pattern in favor of grade 2 metabolic or toxic encephalopathy ( Fig. 1 a) [ 7 ]. Repeated administration of methylene blue was initiated between day 4 and day 7 at a total dose of 800 mg. The outcome was favorable, with progressive improvement in the behavioral symptoms and clinical cognitive impairment, like prosopagnosia, resolving by day 10 with ad integrum restoration of the initial state and residual grade I fatigue [ 6 ]. Figure 2 a shows the evolution of symptoms from the identification of ifosfamide-induced encephalopathy. Electroencephalography (conventional longitudinal bipolar montage, sensitivity 100 μV/cm, high-pass filter 0.530 Hz, low-pass filter 70 Hz) on presentation demonstrating: a Day 4: a continuous, symmetrical pattern, characterized by a background theta-band rhythm at 4–5 cycles/s, diffuse, reactive with acceleration to stimulation. Added to this is bilateral slow delta activity, sometimes taking on an anterior triphasic character (framed in a red rectangle), reactive with disappearance on stimulation. Tracing in favor of metabolic or toxic encephalopathy, grade 2. b Day 7: slowed symmetrical continuous background rhythm in the theta-band at 6 cycles/s, diffused, but reactive to eye opening/closing. No paroxysmal features added. Overall slowed trace grade 1 toxic or metabolic encephalopathy, with a clear improvement compared to day 4. c Day 10: continuous pattern. Background rhythm within the alpha band at 8–9 cycles/s, bilaterally symmetrical posteriorly modulated and reactive. No slow activity, no paroxysmal features or seizure. Normalization of EEG trace with disappearance of metabolic/toxic abnormalities. a Timeline showing the evolution of clinical symptoms by day from the identification of ifosfamide-induced encephalopathy on day 4. Clinical grades are analyzed according to CTCAE V5.0 [ 6 ]. b Timeline of ifosfamide-induced encephalopathy started on day 4 of onset of adjuvant chemotherapy until day 11. NSE in bleu is measured in microgram per liter assessed on days 5, 8, and 10. Electroencephalographic toxic or metabolic grades in orange have been assessed on days 4, 7, and 10. Clinical encephalopathy grade according to CTCAE V5.0 in gray has been assessed daily. Trend curves are shown as dotted in the corresponding color. The improvement in clinical condition was consistent with the improvement in the EEG pattern from grade 2 on day 4 to grade 1 on day 7 to complete normalization on day 10 ( Fig. 1 , 2 b). Concurrent NSE levels in peripherical blood sample declined and were consistent with improvement of clinical conditions from 20.4 µg/L on day 4, down to 11.78 µg/L on day 8, and 7.69 µg/L on day 10 ( Fig. 2 b). The patient’s hospitalization was prolonged due to grade 4 hematotoxicity complicated by febrile aplasia and cisplatin-induced acute kidney injury, which had a favorable outcome [ 6 ]. To date, the patient is asymptomatic and has had no signs of clinical or radiographic relapse of osteosarcoma. The patient medical history timeline is presented in Figure 3 . Patient medical history timeline.

The patient agreed to the publication of this case report and participated in data collection to ensure the accuracy of the report. Ethical approval was not required for the study involving humans in accordance with the local legislation and institutional requirements. Written informed consent to participate in this study was not required from the participants in accordance with the national legislation and the institutional requirements. Written informed consent was obtained from the patient for publication of this case report and any accompanying images. This case report follows the CARE Guidelines. The CARE Checklist has been completed by the authors, attached as online supplementary material (for all online suppl. material, see https://doi.org/10.1159/000546305 ).

Arthur Claessens: conception of the work; acquisition and interpretation of data for the work; and drafting the work. Agathe Manchart, Audrène Bergeot and Anne Kieffer: interpretation of data for the work and reviewing it critically for important intellectual content. Mahira Boufraine and Ariane Guignard: acquisition of data for the work and reviewing it critically for important intellectual content. Aurélien Lambert: conception of the work and reviewing it critically for important intellectual content. All the authors gave final approval of the version to be published and agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.