Preganglionic lesions have a better prognosis than postganglionic lesions* o Preanlionic Brachial Plexus Injury. o - preganglionic lesions represent root avulsions from the spinal cord o - preganglionic injuries have limited spontaneous recovery; o - surgical repair is impossible (bad pregnosis as compared to post-ganglionic lesion) o -- Exam. findings include: o - abnormal axonal reflex; o - Horner's syndrome: (pre-ganglionic injury) o - caused by avulsion of the T1 root resulting in interruption of the T1 sympathetic ganglion; o - results in interruption of sympathetic nerve supply to the eye; o - causes miosis (constriction of pupil), ptosis (dropping of upper eyelid), enophthalmos (sinking of the orbit), and anhydrosis (dry eyes); o - Diagnostic Studies: o -EMG: o - nerve conduction studies show absent motor conduction with intact sensory conduction; o - afferent sensory fibers will not undergo Wallerian degeneration following nerve root avulsion because cell bodies of afferent sensory fibers are located in dorsal root anlion which resides distally; o -if nerve conduction velocity demonstrates absence of both sensory and motor then lesion is pQj ganglionic; o - histamine test: o - differentiate preganglionic and postganglionic lesions; o - if the nerve is interrupted proximal to ganglion, there is anesthesia along its cutaneous course, but the normal axon response will be seen; o - normal axon response can be demonstrated by placing a drop of histamine on the skin o - the skin is scratched thru the histamine; o - triple response: o - vasodilatation, wheel formation, and flare; o - a sequential response consisting of cutaneous vasodilation and wheal formation are seen, the flare response is present; o - a normal response implies a preganlionic lesion and has a prognosis; o if the flare response is negative then the lesion may be at a site where recovery may be possible after repair