Plexopathies

1. What is neuralgic amyotrophy (= Parsonage-Turner = brachial neuritis)?
2. How do you distinguish neoplastic from radiation plexopathy?
3. How does a root avulsion present, and what is the most common site?
4. What nerve roots make up the lumbar and sacral plexus?
5. What are common causes of lumbosacral plexus injury?

Answers:
1. Involves various nerves of brachial plexus, of unknown etiology, presenting with acute onset of intense pain and weakness at shoulder girdle, exacerbated by abduction and rotation. EMG may show abnormal spontaneous activity in the distribution of a mononeuropathy or a plexopathy.
2. Neoplastic plexopathy usually occurs in the lower trunk, is painful, and presents with Horner's syndrome. Radiation plexopathy can occur months or years post-radiation, occurs in the upper trunk, is painless, and presents with myokymia.
3. Root avulsion can occur with a severe plexus injury, most commonly occurring in C8 and T1 because they have the least connective tissue protection. It presents as absent sensation or muscle contraction from the muscles innervated by the involved roots. SNAPs are normal, but CMAPs are absent. EMG shows absent recruitment and abnormal spont activity in a myotonic distribution, including the paraspinals.
4. Lumbar plexus: L1-L4. Sacral plexus: L4-S4.
5. Neoplastic plexopathy, radiation plexopathy, neuralgic amyotrophy, retroperitoneal bleed, hip dislocation, obstetric injuries.