Plexopathy
Plexopathy
Lesions confined to the brachial, lumbar, or sacral plexi may produce a constellation of motor and sensory signs (weakness, reflex diminution or loss, sensory loss) which cannot be ascribed to single or multiple roots (radiculopathy) or peripheral nerves (neuropathy). Lesions may involve the whole plexus (panplexopathy):
Brachial: C5-T1 Lumbar: L2-L4 Sacral: L5-S3
or be partial, e.g., upper trunk of brachial plexus (C5-C6), producing "waiter’s tip" posture (as for C5/C6 root avulsion); lower trunk of brachial plexus (C8-T1; as for C8/T1 root avulsion).
Electrophysiological studies may be helpful in distinguishing plexopathy from radiculopathy: sensory nerve action potentials (SNAPs) are reduced or absent in plexopathies because the lesion is located distal to the dorsal root ganglion (DRG), whereas SNAPs are normal in radiculopathies because the lesion is proximal to the DRG. EMG shows sparing of paraspinal muscles in a plexopathy because the lesion is, by definition, distal to the origin of the dorsal primary rami (cf. radiculopathy). Coexistence of radiculopathy and plexopathy may invalidate these simple rules.
- Recognized causes of brachial plexopathy include:
Trauma: Upper plexus: Dejerine-Klumpke paralysis ("waiter’s tip" posture);
Lower plexus: Erb-Duchenne paralysis (claw hand). Inflammation/Idiopathic: brachial neuritis, neuralgic amyotrophy.
Malignant infiltration, e.g., carcinoma of lung (Pancoast), breast, +/− Horner’s syndrome; pain a significant symptom. Post-radiation (e.g., after radiotherapy for malignant breast cancer with axillary spread; myokymic discharges may be seen on EMG).
Tomaculous neuropathy.
Hereditary neuropathy with liability to pressure palsies (HNLPP).
Neurogenic thoracic outlet syndrome (rare): cervical rib or C7 transverse process or fibrous band compressing the lower trunk. May be surgically remediable.
- Recognized causes of lumbosacral plexopathy include:
Compression; e.g., iliopsoas hematoma (anticoagulation, hemophilia), abscess (tuberculosis); abdominal aortic aneurysm; pregnancy (fetal head in the second stage of labor). Neoplasia (direct spread > metastasis).
Trauma (rare; cf. brachial plexopathy). Post-radiation.
Vasculitis (mononeuritis multiplex much commoner). Idiopathic.
Imaging with MRI is superior to CT for defining structural causes of plexopathy.
References
Chad DF. Nerve root and plexus disorders. In: Bogousslavsky J, Fisher M (Eds.). Textbook of neurology. Boston: ButterworthHeinemann, 1998: 491-506
Taylor BV, Kimmel DW, Krecke KN, Cascino TL. Magnetic resonance imaging in cancer-related lumbosacral plexopathy. Mayo ClinicProceedings 1997; 72: 823-829
Cross References
Amyotrophy; Claw hand; Horner’s syndrome; Nerve thickening; Neuropathy; Radiculopathy; "Waiter’s tip" posture
