Exploring phantom phenomena following brachial plexus block in intact limbs

Phantom limb experiences, including phantom limb sensations (PLS) and phantom limb pain (PLP), are common after limb amputation or deafferentation, with PLP significantly impacting quality of life. However, the mechanisms underlying PLP remain unclear, complicating treatment development. Investigating phantom phenomena has been proposed to gain insights into the mechanisms behind the insurgence of PLS and PLP, potentially informing new therapeutic approaches. However, small, heterogeneous samples and a lack of objective pain metrics often limit research on individuals with limb loss. Here, we investigate whether phantom experiences, similar to those reported after amputation, also occur in individuals with intact limbs following a brachial plexus nerve block, excluding the brain from afferent and efferent signals.

To investigate the phenomenon, we conducted a multifaceted phenomenological study involving 14 individuals undergoing elective hand or arm surgery under brachial plexus nerve block. Participants were asked to report on the presence of phantom experiences and describe them in terms of vividness, quality, position, telescoping, movements, and pain. Assessments occurred at four-time points: before surgery, during surgery, after surgery, and at home. These findings were then compared to observations in the amputation population.

93 % of the participants reported PLS 20-40 min following brachial plexus anesthesia. The most frequently reported qualities of PLS were tingling, heaviness, and warmth. Commonly reported experiences after limb loss, such as distorted limb position, telescoping, and execution of phantom limb movements, were also reported by the participants after the deafferentation. Notably, participants experiencing distorted limb positions did not find them painful or uncomfortable. PLP was reported by only one participant.

This study demonstrates that individuals with temporary sensorimotor deafferentation via brachial plexus nerve block experience many phantom phenomena similar to those reported by individuals with limb loss. This suggests that brachial plexus nerve block is a promising model for studying PLP and a potential test bed for its treatment.