The Prediction of Clinical Outcome Using the Serum BDNF Level

Low back pain (LBP) is one of the most commonly observed conditions in patients over the age of 50 and imposes a substantial socioeconomic burden. Degenerative disc disease is one of the most frequent and important causes of this pain. Progressive disc degeneration is characterized by a decline in disc cell number and degradation of the extracellular matrix. Loss of nucleus pulposus (NP) volume and hydration, together with fissure formation within the annulus fibrosus (AF), develop gradually with aging and ultimately lead to functional impairment. Disc degeneration can result from multiple factors, including aging, obesity, genetic predisposition, degeneration of the multifidus and psoas muscles, osteoporosis, inflammation, and oxidative stress. The intervertebral disc consists of the gel-like nucleus pulposus (NP) at its center, the surrounding annulus fibrosus (AF), and the cartilaginous endplates above and below. Because the disc is an avascular structure, its capacity for self-repair is markedly limited.

Erector spinae plane block (ESPB) is a treatment option that can be performed in the outpatient setting for patients with such low back pain. ESPB was first described in 2016 and is a type of interfascial plane block. Unlike neuraxial blocks, it offers the advantage of being both technically straightforward and highly safe. Recent studies indicate that ESPB is increasingly applied to patients with post-spinal-surgery pain or chronic low back pain.

Brain-derived neurotrophic factor (BDNF) is a neurotrophin that regulates neuronal survival, differentiation, and synaptic plasticity within the central nervous system. In the context of pain, BDNF released from primary afferent nociceptors and spinal dorsal horn microglia has been implicated in central sensitization, a key mechanism underlying the transition from acute to chronic pain. Circulating BDNF concentrations have been reported to be associated with pain intensity, disability, and cortical/corticomotor plasticity in patients with chronic low back pain, and some studies have found serum BDNF levels to be significantly elevated in discogenic chronic low back pain compared with controls, while others report reduced circulating BDNF in chronic pain populations - suggesting that the relationship between BDNF and pain chronicity may vary by pain phenotype and warrants further clarification. Because BDNF reflects neuroplastic changes that accompany the development and persistence of chronic pain, it has been proposed as a potential predictor of treatment response. However, no study to date has directly examined whether serum BDNF concentration can predict the clinical outcome of ESPB in patients with low back pain.