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To the Editor: LaFrance et al.1 reported lower plasma brain-derived neurotrophic factor (BDNF) levels in patients with epileptic seizures (ES) and psychogenic nonepileptic seizures (PNES) than healthy controls (HCs). Reduced BDNF in the plasma may be used to differentiate patients with ES and PNES from HCs, and probably from malingerers. However, the small sample size in this study is concerning.
Gender and age differences should be considered. Due to the small sample size, stratified analysis seems unlikely. Plasma levels of BDNF vary between different phases of the menstrual cycle.2 It has also been shown that increasing age was associated with reduced levels of plasma BDNF.3 The gender differences and Beck Depression Inventory II (BDI-II) score may partially explain the differences of plasma BDNF levels between patients with ES or PNES and HCs.
Although the authors stated that seizure frequency and temporal proximity did not influence the BDNF levels in either the PNES or ES group, the time point to obtain the blood samples was not consistent. Multiple studies have confirmed increased expression of BDNF after seizures.4
Confounders may have influenced the data interpretation. Determinants in the measurement of plasma BDNF include fasting/nonfasting state of blood draw, earlier/later measurement, and sample storage time.5 Studies on these levels should correct for …
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