Which statement correctly distinguishes AMAN from AIDP?

• A. AMAN selectively targets motor axons, whereas AIDP involves demyelination of peripheral nerves
• B. AMAN affects CNS
• C. AMAN is purely sensory
• D. AIDP is purely motor

Answer: (C)

The distinguishing idea is that AMAN is an acute motor axonal neuropathy, meaning the pathology is focused on motor nerve fibers at the axon level, leading to prominent weakness with little or no sensory loss. AIDP, in contrast, is a demyelinating process of the peripheral nerves, which can affect both motor and sensory fibers because the myelin around many nerves is involved.

This makes the statement that AMAN selectively targets motor axons while AIDP involves demyelination of peripheral nerves the best fit. Clinically, that translates to AMAN often presenting with relatively pure motor weakness and minimal sensory symptoms, whereas AIDP can include sensory disturbances as part of the demyelinating process. Electrophysiology supports this too: AMAN tends to show reduced motor nerve action potential amplitudes with preserved sensory potentials, reflecting motor axonal involvement, while AIDP shows features of demyelination such as slowed conduction and possible involvement of sensory nerves.

The other options don’t match the typical patterns: AMAN does not affect the CNS; it is not purely sensory; and AIDP is not purely motor.