Sensory pathophysiology in chronic acquired demyelinating neuropathy

Area of Science:

• Neuroscience
• Neurology
• Clinical Electrophysiology

Background:

• Pathophysiology of sensory fibers in chronic acquired demyelinating neuropathy (CADP) remains unclear.
• Distinguishing axonal loss from conduction block in sensory loss is challenging.
• Understanding nerve conduction abnormalities is crucial for CADP diagnosis and management.

Purpose of the Study:

• To investigate and delineate abnormalities in sensory and motor nerve conduction in CADP patients.
• To differentiate the contributions of axonal loss and demyelination to sensory loss and motor dysfunction.
• To analyze proximal versus distal nerve conduction parameters in CADP.

Main Methods:

• Studied motor and sensory nerve conduction in 18 CADP patients.
• Utilized near-nerve needle electrodes and electronic averaging to record compound sensory action potentials (CSAPs).
• Compared proximal and distal nerve conduction parameters, including amplitude ratios and velocities, in upper and lower limbs.

Main Results:

• Reduced proximal/distal amplitude ratio (P/D ratio) of compound muscle action potentials (CMAPs) in 76% of nerves, versus 21% for CSAPs.
• Proximal motor nerve conduction velocity (MCVp) reduction (40-50%) was twice the distal MCV (MCVd) reduction, linked to P/D ratio.
• Proximal sensory nerve conduction velocity (SCVp) reduction (~20%) was disproportionate to motor nerve changes, suggesting distinct mechanisms.

Conclusions:

• Sensory nerve dysfunction in CADP is predominantly due to nerve fibre loss (axonal loss).
• Motor nerve dysfunction in CADP is primarily caused by demyelination.
• CADP exhibits different pathophysiological mechanisms affecting sensory and motor nerve fibers.