Somatosensory Misalignment: Persistent Referred Sensation After Intercostal-to-Musculocutaneous Nerve Transfer

Area of Science:

• Neuroscience
• Regenerative Medicine
• Sensory Physiology

Background:

• Referred sensation (RS) is sensation felt in areas distant from the stimulation site.
• Traumatic brachial plexus injury (TBPI) can disrupt normal sensory pathways.
• Understanding RS patterns is crucial for assessing nerve regeneration outcomes.

Purpose of the Study:

• To systematically identify and map referred sensations (RS) in patients with traumatic brachial plexus injury (TBPI).
• To investigate the characteristics and distribution of RS following specific nerve transfer procedures.
• To explore the relationship between cortical representation and sensory reorganisation after nerve injury.

Main Methods:

• An observational study involving RS screening using cotton swabs on 19 TBPI participants.
• Comprehensive RS mapping with Semmes-Weinstein monofilaments on reinnervated forearms in three subjects.
• Longitudinal assessment of RS mapping over 6.3 years in one participant.

Main Results:

• Referred sensations (RS) were reported in participants undergoing intercostal-to-musculocutaneous nerve (ICN-MCN) and ulnar-to-musculocutaneous nerve (UN-MCN) transfers.
• Persistent 'right-way' RS (within the donor nerve's original territory) was observed after ICN-MCN transfer.
• RS mapping showed a distinct, non-topographical distribution in the forearm and chest, with gradual expansion over time in one case.

Conclusions:

• This study presents the first systematic mapping of RS in TBPI patients.
• Persistent 'right-way' RS suggests that significant distances between nerve representations in the primary somatosensory cortex (S1) may impede plastic reorganisation.
• Findings highlight the complexity of nerve regeneration and inform future therapeutic strategies for sensory function restoration.