- 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 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;
