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Duke Orthopaedics
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Wheeless' Textbook of Orthopaedics

Preganglionic Brachial Plexus Injury


- Discussion:
    - preganglionic lesions represent root avulsions from the spinal cord;
    - 2 catagories:
         - central avulsions: nervs are avulsed directly from the spinal cord;
         - intradural ruptures: rootlets are ruptured proximal to the dorsal root ganglion;
    - preganglionic injuries have limited spontaneous recovery;
    - injuries in which roots of upper plexus are avulsed from spinal cord should always be recognized, because surgicalal repair is impossible;
    - differential dx:
           - C6 root lesions may mimic a brachial plexus lesion;
           - elbow flexion is weak, & the pt is unable to supinate forearm against resistance with the elbow held in extension;


- Exam: findings c/w preganglionic lesions include:
    - anesthesia above the clavicle
    - horner's syndrome: (pre-ganglionic injury)
         - caused by avulsion of the T1 root resulting in interruption of the T1 sympathetic ganglion;
         - results in interruption of sympathetic nerve supply to the eye;
         - causes miosis (constriction of pupil), ptosis (dropping of upper eyelid), enophthalmos (sinking of the orbit), and anhydrosis (dry eyes);
    - abnormal axonal reflex;
    - winging of scapula: (serratus anterior)
    - weak levator scapula & rhomboids:
    - elevated hemidiaphragm (determined from CXR);


- Diagnostic Studies:
    - EMG:
         - denervating potentials in the segmental paraspinal muscles innervated by the posterior primary rami;
         - nerve conduction studies:
                 - NCS shows absent motor conduction w/ intact sensory conduction;
                 - afferent sensory fibers will not undergo Wallerian degeneration following nerve root avulsion becuase because cell bodies of afferent
                            sensory fibers are located in dorsal root gangion which resides distally;
                 - if nerve conduction velocity demonstrates absence of both sensory and motor then lesion is post gangionic;
    - myelogram:
         - may be diagnostic be should be delayed 6-12 wks, since a clot of blood may occlude the opening of the pseudomenigocele;
    - histamine test:
         - differentiate preganglionic and postganglionic lesions;
         - if the nerve is interrupted proximal to ganglion, there is anesthesia along its cutaneous course, but the normal axon response will be seen;
         - normal axon response can be demonstrated by placing a drop of histamine on the skin;
         - the skin is scratched thru the histamine;
         - triple response:
                 - vasodilatation, wheel formation, and flare;
                 - a sequential response consisting of cutaneous vasodilation and wheal formation are seen, the flare response is present;
                 - a normal response implies a preganglionic lesion and has a poor prognosis;
                 - if the flare response is negative then the lesion may be at a site where recovery may be possible after repair



Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Thursday, December 15, 2011 11:18 am