radiculopathy and plexopathy

Recall the wiring chain: roots leave the spine, braid together in the plexus, then sort into the named peripheral nerves. A radiculopathy is a problem at a root, usually where a disc or bony overgrowth pinches it as it exits the spine, the typical cause of a pain shooting down one arm or leg. A plexopathy is a problem in the braided junction itself, the brachial plexus near the shoulder or the lumbosacral plexus in the pelvis, from injury, inflammation, or a tumour pressing on it. Both sit upstream of the peripheral nerves, which makes them harder to pin down by feel alone.

Electrodiagnosis localizes these by exploiting the wiring diagram. The single most useful trick uses the dorsal root ganglion, the cluster of sensory cell bodies just outside the cord. A root pinch is usually above this cluster, so the sensory fibre below stays connected to its cell body and the SNAP stays normal even though the limb is numb; a normal SNAP in a numb limb therefore points to a root, not a nerve or plexus. The needle exam then maps the damage: in a radiculopathy, denervation lines up by root level across several different peripheral nerves, and crucially includes the small muscles right beside the spine (the paraspinals), which are supplied directly off the root before the plexus. In a plexopathy the SNAPs are abnormal and the pattern spans more than one root but spares the paraspinals.

These are common, important referrals, because a radiculopathy from a neck or back problem can mimic a peripheral entrapment, and a plexopathy can masquerade as several separate nerve injuries. The study clarifies the level and helps gauge severity and timing, but it has real limits: it samples motor fibres best and may stay normal in a purely painful, sensory, or very mild radiculopathy, so a normal study never rules out a root problem that imaging or the clinical picture still supports.