Clinical Presentation and Diagnosis of Plexopathy

Anatomical Context

The brachial plexus is formed from C5-T1 ventral rami, with nerve roots passing between anterior and middle scalene muscles with the subclavian artery to form trunks, divisions, cords, and terminal branches, as described by the American College of Radiology 1, 2
The lumbosacral plexus is comprised of lumbar and sacral plexuses connected via the lumbosacral trunk, formed from L1-L5 ventral rami with contributions from T12 and S1-S4, according to the American College of Radiology 1, 3

Neuropathic pain occurs in multiple peripheral nerve distributions, such as shoulder/arm or back/leg, as reported by the American College of Radiology 1, 3
Pain distribution crosses multiple dermatomes, distinguishing it from radiculopathy, as noted by the American College of Radiology 4

Weakness occurs in regions innervated by multiple nerves from the affected plexus, as described by the American College of Radiology 1
Complete plexopathy causes flaccid weakness in the distribution of multiple peripheral nerves, according to the American College of Radiology 3

Sensory loss occurs across multiple nerve distributions, as reported by the American College of Radiology 1, 3

Flaccid loss of tendon reflexes occurs in regions innervated by the affected plexus, as described by the American College of Radiology 1, 3

Pain and weakness occur in the shoulder and arm, as reported by the American College of Radiology 3
Weakness and sensory loss occur in the C5-T1 distribution, according to the American College of Radiology 2, 3

Pain and weakness occur in the back, hip, and leg, as described by the American College of Radiology 1, 3
Weakness occurs in muscles of the anterior/medial thigh or gluteal region/posterior thigh/lower leg, as reported by the American College of Radiology 1

Clinical diagnosis is confirmed by electrodiagnostic studies, as described by the American College of Radiology 1, 3
MRI is the mainstay of plexus imaging, providing superior definition of intraneural anatomy, according to the American College of Radiology 3, 4

Traumatic, neoplastic, inflammatory/immune-mediated, radiation-induced, diabetic, vascular, infectious, hereditary, or idiopathic causes are possible, as reported by the American College of Radiology 1, 2, 5

The American College of Radiology recommends MRI of the lumbosacral plexus as the gold standard imaging modality for diagnosing lumbosacral plexopathy due to its superior soft-tissue contrast and ability to visualize intraneural anatomy when clinical and electrodiagnostic findings are nonspecific 6, 7, 8
MRI lumbosacral plexus provides superior soft-tissue contrast and spatial resolution, and can detect abnormal intraneural signal and localize pathologic lesions 8
IV contrast helps characterize masses, tumors, and inflammatory conditions during MRI lumbosacral plexus 7
When the initial diagnosis is uncertain, MRI lumbar spine may be performed first, as it has a higher prevalence of radiculopathy-related degenerative spine disease, but note that lumbar spine MRI does not evaluate the plexus lateral to the neural foramina 7
CT with IV contrast offers the next highest level of anatomic visualization when MRI is contraindicated, and is useful for detecting soft-tissue masses and tumors, but is limited in visualizing intraneural anatomy compared to MRI 7

Studies show that MRI lumbosacral plexus leads to changes in diagnosis in 78% of patients and changes in management in 71-81% of patients, highlighting the importance of proper imaging in diagnosing lumbosacral plexopathy 6
Combining MRI and electrodiagnostic studies significantly improves diagnostic accuracy, according to the American College of Radiology 6