Serum Neurofilament Light Chain Tracks Acute Injury in Refractory Status Epilepticus

Quantifying the Hidden Toll of Refractory Status Epilepticus

Status epilepticus is a neurological emergency where prolonged seizure activity triggers a cascade of irreversible neuronal death and network alterations [1]. While animal models clearly demonstrate this seizure-induced injury, clinical evidence in humans has historically been limited to small case series, leaving a gap in our ability to quantify real-time brain damage [1, 2]. The challenge is particularly acute in cases of new-onset refractory status epilepticus, where the absence of a clear etiology complicates both treatment and prognosis [3]. Identifying reliable biomarkers of neuro-glial injury is essential for early risk stratification and the potential validation of neuroprotective strategies [1, 4]. Recent advances in fluid biopsy techniques have introduced candidates like neurofilament light chain and S100-beta as potential tools for monitoring acute brain injury in the intensive care unit [5, 6]. A large-scale international study has now evaluated these biomarkers to clarify the trajectory of neuronal damage in patients facing the most severe forms of refractory seizures.

A Multi-Center Analysis of Neuro-Glial Biomarkers

To investigate the biochemical signatures of seizure-induced brain injury, researchers conducted an international cross-sectional study between 2013 and 2025. The study enrolled participants across a network of 36 hospitals in the United States, two in Canada, and one each in Italy, France, and Belgium. The primary focus was on 78 patients with cryptogenic new-onset refractory status epilepticus (cNORSE), a condition characterized by prolonged seizures without an immediately identifiable cause. This cohort had a mean age of 37 years (95% CI, 30 to 41) and was 56% female (44 patients). To provide a robust clinical comparison, the researchers also included two independent cohorts of patients with etiology-defined status epilepticus (eSE), where the underlying cause of the seizures was known. The first eSE cohort consisted of 211 patients with a mean age of 69 years (95% CI, 66 to 71), of whom 128 (61%) were female. The second eSE cohort included 73 patients with a mean age of 56 years (95% CI, 45 to 65), including 39 males (53%). The study further utilized comparison groups without status epilepticus, comprising individuals with chronic epilepsy and healthy participants, to establish baseline biomarker levels. Investigators focused on two specific proteins to index the degree of neurological damage: neurofilament light chain (NfL), a structural protein found in the axons of neurons that serves as a specific marker of neuroaxonal injury, and S100-beta (S100B), a calcium-binding protein primarily expressed by astrocytes that indicates glial injury or blood-brain barrier disruption. These concentrations were measured in both serum and cerebrospinal fluid (CSF) obtained during ongoing seizure activity, allowing the team to correlate these biological signals with acute clinical status and short-term functional outcomes.

Marked Elevation of Neurofilament Light Chain in cNORSE

The study demonstrated that neurofilament light chain concentrations in the cerebrospinal fluid were approximately 10-fold higher in patients with cryptogenic new-onset refractory status epilepticus compared with those in the etiology-defined status epilepticus cohorts. Specifically, patients with cryptogenic new-onset refractory status epilepticus exhibited a median cerebrospinal fluid neurofilament light chain level of 6408 pg/mL (interquartile range, 1503 to 22,963 pg/mL), whereas the etiology-defined status epilepticus cohorts showed a median of 694 pg/mL (interquartile range, 219 to 2389 pg/mL; P < .001). A similar disparity was observed in systemic circulation, where serum neurofilament light chain concentrations were approximately 4-fold higher in the cryptogenic new-onset refractory status epilepticus group, reaching a median of 231 pg/mL (interquartile range, 99 to 855 pg/mL) compared to 55 pg/mL (interquartile range, 20 to 135 pg/mL) in the etiology-defined status epilepticus cohorts (P < .001). When compared to individuals without active status epilepticus, the magnitude of neuroaxonal injury in cryptogenic new-onset refractory status epilepticus was even more pronounced. Serum neurofilament light chain levels were nearly 20-fold higher in the cryptogenic new-onset refractory status epilepticus cohort than in patients with chronic epilepsy, who had a median level of 11 pg/mL (interquartile range, 7 to 19 pg/mL), and healthy controls, who had a median level of 7 pg/mL (interquartile range, 5 to 14 pg/mL). For the clinician, these findings are reinforced by the fact that serum and cerebrospinal fluid neurofilament light chain levels were strongly correlated (Spearman ρ = 0.75; P < .001). This robust correlation indicates that serum sampling can serve as a reliable, less invasive proxy for cerebrospinal fluid analysis when monitoring the intensity of acute axonal damage in these patients.

Temporal Dynamics and Diagnostic Accuracy

The longitudinal analysis of serum neurofilament light chain levels revealed a progressive and rapid escalation of neuroaxonal injury during the acute phase of the illness. Serum neurofilament light chain levels in patients with cryptogenic new-onset refractory status epilepticus rose sharply over the first three weeks following onset, with median concentrations increasing from 101 pg/mL (interquartile range, 51 to 137 pg/mL) in week 1 to 197 pg/mL (interquartile range, 117 to 324 pg/mL) in week 2, and reaching 598 pg/mL (interquartile range, 163 to 1000 pg/mL) by week 3 (P < .001). This steep trajectory suggests that the window for neuroprotective intervention may be narrow, as the biochemical evidence of neuronal damage intensifies significantly within days of the initial presentation. In contrast to the dynamic changes observed with neurofilament light chain, S100-beta concentrations did not differ between groups and showed no consistent temporal pattern, suggesting that this glial marker may be less sensitive for tracking the specific progression of injury in this clinical context. The diagnostic utility of neurofilament light chain was further quantified through its area under the receiver operating characteristic curve (a statistical measure of how well a test distinguishes between two groups, where 1.0 represents perfect accuracy). Neurofilament light chain discriminated cryptogenic new-onset refractory status epilepticus from etiology-defined status epilepticus with an area under the receiver operating characteristic curve of 0.79 (95% CI, 0.68 to 0.90). The biomarker demonstrated even higher precision when distinguishing these patients from cohorts without status epilepticus, yielding an area under the receiver operating characteristic curve of 0.99 (95% CI, 0.78 to 1.00). These statistical measures indicate that neurofilament light chain is a highly specific indicator of the severe neuroaxonal damage characteristic of cryptogenic new-onset refractory status epilepticus.

Prognostic Implications for Clinical Practice

The clinical utility of monitoring serum neurofilament light chain extends beyond diagnostic differentiation to the prediction of functional recovery. The researchers found that higher serum neurofilament light chain concentrations were independently associated with poor functional outcomes at the time of hospital discharge. This association was quantified using the Glasgow Outcome Scale extended, a standardized eight-point scale used to assess the functional status of patients after brain injury. For this analysis, a poor outcome was defined as a score between 1 and 4, representing states ranging from death to severe disability requiring daily assistance. The statistical analysis yielded an odds ratio of 1.01 (95% CI, 1.00 to 1.03; P = .03), indicating that incremental increases in this biomarker of axonal damage correlate with a diminished likelihood of achieving functional independence by discharge. Collectively, these findings suggest that acute neuroaxonal injury is substantially greater in patients with cryptogenic new-onset refractory status epilepticus than in those with etiology-defined status epilepticus or controls without status epilepticus. Because neurofilament light chain levels rise so rapidly in the first three weeks of the disease course, the data highlight a narrow therapeutic window for clinicians. This biochemical evidence of accelerating neuronal damage emphasizes the necessity for prompt and aggressive medical management. For the practicing neurologist or intensivist, these results suggest that early and potentially neuroprotective interventions may be critical in mitigating the severe, ongoing brain injury that characterizes the acute phase of cryptogenic new-onset refractory status epilepticus.

References

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