RESEARCH REPORT POSTER DISPLAY

VASOMOTOR INNERVATION PATTERNS BY PERIPHERAL NERVES SUPPLYING THE UPPER AND LOWER EXTREMITIES. Allen R, Jefferson E, Bhangu V; University of Puget Sound, Tacoma, WA, USA

PURPOSE: The purpose was to map vasomotor innervation fields for peripheral nerves supplying the upper and lower extremities and compare these surface neurovascular patterns to somatosensory distributions. RELEVANCE: Knowledge of sensory nerve distribution topography is essential to diagnosing peripheral complaints with neurologic origins. Existing innervation maps present only somatosensory fields. When complaints do not fit known patterns, nonorganic etiology is sometimes erroneously suspected. Variations in sympathetic nerve activity to limb arterioles may result in symptoms of ischemic pain, numbness, or paresthesias following neurovascular rather than somatosensory distributions. PARTICIPANTS: Participants included 31 female and 13 male volunteers, ages ranging from 27 to 64 years (x = 35.7), reporting no history of amine-type anesthetic hypersensitivity, peripheral neuropathy, vascular pathology or insufficiency, chronic limb pain, or hypertension. Upper extremity mapping involved 32 participants and 12 participated in mapping the lower extremity. METHODS: Nerves investigated were the median, radial, ulnar, musculocutaneous, lateral antebrachial cutaneous, axillary, femoral, lateral femoral cutaneous, obturator, tibial, saphenous, deep and superficial fibulars, medial calcaneal, and medial and lateral plantars. The procedure involved blockade of each nerve via tissue infiltration of Carbocaine hydrochloride to the nerve’s most proximal selective location, followed by infrared digital thermographic imaging of the resultant region of superficial hyperemia. Neural blockade temporarily interrupted local sympathetic innervation to arteries supplied by the nerve, resulting in vasodilation and hyperemia. Hyperemia regions represented the vascular innervation field of the nerve. Manual muscle testing and Semmes Weinstein monofilaments were used to validate success and selectivity of each block. ANALYSIS: Pre-blockade thermographic stabilization images were digitally compared to post-blockade thermograms for changes in surface temperature. Areas with increases of >3 degrees centigrade were assembled to represent the vasomotor innervation field for the blocked peripheral nerve. Innervation fields for the nerves under investigation were compiled to produce a map of vasomotor innervation patterns for each extremity. RESULTS: In many cases, vasomotor innervation fields corresponded to established somatosensory patterns, with several clinically relevant differences revealed in both limbs. No evidence was found for vasomotor innervation by the radial nerve distal to the wrist, with innervation to the hand supplied solely by the median and ulnar nerves. In the lower extremity, no hyperemia was observed following lateral femoral cutaneous or obturator nerve blockades, leaving the entire anteromedial to anterolateral thigh innervated by the femoral nerve. Post-blockade hyperemia patterns of the deep fibular nerve indicated that it innervates arterioles of the anterior leg and dorsum of the foot. CONCLUSIONS: Peripheral nerves supplying the hand, anterior thigh and leg, and foot’s dorsum display vasomotor innervation patterns notably different from somatosensory distributions. These findings are consistent with the hypothesis that peripheral nerves innervate adjacent principal arteries. IMPLICATIONS: Since vasomotor innervation fields differ from those of somatosensation, neuropathies involving sympathetic efferents may produce symptom patterns that do not match somatosensory distributions. Resulting symptoms should not lead therapists to suppose the pathology is nonorganic. Sample size and subject consistency now affords presentation of a vasomotor innervation map of the extremities for clinical use. KEYWORDS: Neurovascular, vasomotor innervation, peripheral neuropathy. FUNDING ACKNOWLEDGEMENTS: Release time for the principal investigator to complete this study was funded by a John Lantz Senior Research Fellowship from the University of Puget Sound, Tacoma, WA, USA. CONTACT: rallen@ups.edu

ETHICS COMMITTEE: Institutional Review Board, University of Puget Sound, Tacoma, WA, USA