Clinical Findings That Localize a Lesion to the Plexus
The key clinical finding that localizes a lesion to a plexus rather than a nerve root or peripheral nerve is the presence of neuropathic symptoms (pain, dysesthesia, burning sensations) and motor/sensory deficits affecting multiple peripheral nerve distributions that do not follow a single dermatomal pattern. 1
Distinguishing Features of Plexopathy
Primary Localizing Features:
Multiple peripheral nerve involvement: Symptoms span territories of more than one peripheral nerve that originate from the plexus 1
- For brachial plexus: affects combinations of musculocutaneous, axillary, radial, median, and ulnar nerve territories
- For lumbosacral plexus: affects combinations of femoral, obturator, gluteal, peroneal, and tibial nerve territories
Non-dermatomal distribution: Pain and sensory loss do NOT follow a single spinal nerve root dermatomal pattern 1
- This is the critical distinction from radiculopathy
- Radiculopathy presents with dermatomal pain/sensory loss reflecting single root innervation
Clinical Manifestations Supporting Plexus Localization:
Neuropathic pain in shoulder/arm (brachial) or back/leg (lumbosacral) that crosses multiple nerve territories 1
Dysesthesia and burning/electric sensations affecting multiple peripheral nerve distributions simultaneously 1
Complete plexopathy findings (when severe):
- Weakness in multiple nerve territories
- Sensory loss across multiple nerve distributions
- Flaccid loss of tendon reflexes in affected regions 1
Electrodiagnostic Confirmation
Electrodiagnostic studies are essential for confirming clinical plexopathy diagnosis 1. The EDX examination provides:
Sensory nerve conduction studies (NCS): Most useful for brachial plexus element localization 2
- Abnormal sensory nerve action potentials (SNAPs) exclude isolated radiculopathy
- When SNAPs are abnormal, the lesion must be distal to the dorsal root ganglion (i.e., plexus or peripheral nerve)
Motor NCS abnormalities: Help distinguish plexus from root lesions 2
- Motor NCS abnormalities exceeding sensory NCS abnormalities suggest intraspinal canal lesions (avulsions)
- Balanced motor and sensory involvement favors plexus localization
Common Pitfalls to Avoid
Don't confuse with radiculopathy: If pain follows a strict dermatomal distribution with corresponding single-root motor/sensory findings, consider radiculopathy instead 1
Concomitant carpal tunnel syndrome: Can negate utility of median sensory NCS for brachial plexus localization; rely on motor NCS and needle EMG in these cases 2
Incomplete examination: Must assess all potentially affected nerve territories clinically before concluding plexus involvement 3