Neuropathy after ISB occurs relatively frequently with the reported incidence around 2.84% [4]. However, the symptoms are mostly minor, and rarely is there a severe and persistent neurologic complication after continuous ISB. Previous studies [1, 2] have shown that the incidence of neurologic complications (sensorimotor deficit lasting > 6 months) ranges from 0 to 0.1%, but little information is available on how severe and persistent neuropathy occurs and develops. To the best of our knowledge, this report is the first detailed description of a case who incurred severe and persistent nerve injury after ultrasound-guided continuous ISB yet recovered nearly fully to return to being an athlete.
Perioperative nerve injury results from a multitude of clinical factors, which can be categorized in anesthetic, surgical, and patient factors [5]. The anesthetic factors can be further divided into mechanical factors associated with regional anesthesia or chemical factors related to the neurotoxicity of local anesthetics [6]. In the present case, the injury site estimated from neurophysiological measurements and MRI corresponded almost exactly with the distribution of local anesthetic by nerve block. In addition, our patient was a healthy teenager and the operation was performed uneventfully. Both an intraneural injection and a plexus compression due to hematoma were excluded by ultrasonography, but there is a possible involvement of other unknown factors. Therefore, we speculate that it is highly likely that local anesthetic continuously delivered to the nerve roots resulted in severe and persistent neuropathy together with other unknown factors.
In the present case, although local anesthetic was administered in a clinical dose, severe and persistent neuropathy still occurred. It is worthy of note that the patient felt no pain even when we moved his shoulder during 48 h. It is uncommon that pain intensity is so low after shoulder surgery even during continuous ISB. Our unpublished data show that VAS pain scores after arthroscopic shoulder surgery were 40 ± 31 (mean ± standard deviation) mm and 35 ± 21 mm at 24 and 48 h, respectively, on movement during continuous ISB using the same regimen as the present case. We should have noticed a possibility that something was going wrong when we checked the patient at 24 h. Studies have shown that all local anesthetics are potentially neurotoxic [7, 8] and that local anesthetic exhibits dose and time-dependent toxicity to nerves [7,8,9]. Therefore, it is possible that if we had discontinued the infusion earlier, i.e., at 24 h postoperatively, the damage might have been less serious.
Seddon classified nerve injuries into three major groups: neurapraxia, axonotmesis, and neurotmesis [10]. Sunderland proposed a more detailed classification [11], further dividing Seddon’s axonotmesis category into injuries with intact endoneurium, disrupted endoneurium but intact perineurium, and disrupted inner connective tissue layers with intact epineurium. These axonotmesis injuries of varying severity were designated types 2 to 4, from least to most severe. Sunderland referred to Seddon’s neurapraxia as a type 1 and neurotmesis as a type 5. It has been reported that when a large dose of lidocaine was administered continuously into the epidural space in rats, the specimen from the nerve roots showed edema, axonal degeneration, disintegrated myelin lamellae, and degenerated Schwann sheaths, with the continuity of the outer membrane of the fascicles being maintained [9]. These findings are equivalent to Sunderland type 3 injury in which recovery can occur over several months with conservative treatment or with surgical interventions to release entrapment sites [12]. From the clinical course and findings of neurophysiological assessments and MRI, we speculate that the nerve injury of this case is equivalent to a Sunderland type 3 injury. Despite previous reports [13, 14] showing poor recovery, in a case of severe and persistent neuropathy due to the toxicity of local anesthetic like this case, recovery can be expected with conservative treatment without surgical interventions. Therefore, it is important to continue treatment with hope of recovery without giving up.
During long-term management, maintaining motivation was crucial. Factors, such as having a clear goal of returning to play soccer, continuing to receive support from family and medical staff involved, confirming recovery process through detailed neurophysiological measurements, managing neuropathic pain, and rigorous rehabilitation, must have contributed to maintaining motivation and nearly a full recovery was observed 1 year after the incident.
