Disclosure Entrapment Neuropathies - Overview I receive compensation from Wiley- Blackwell publishers for my work as Editor-in-Chief of Muscle & Nerve Lawrence H. Phillips, II, MD Definitions Mononeuropathy: damage to a single nerve or nerve group which results in loss of movement, sensation or other function of that nerve Entrapment neuropathy: a medical condition caused by direct pressure on a single nerve as a result of chronic compression or mechanical injury at a specific site. Signs & sx affected by specific factors at different anatomic sites wrist Carpal Tunnel Syndrome Most common mononeuropathy Model for entrapment Conduction properties differ at specific sites in the nerve wrist Ulnar nerve at the elbow Cubital Tunnel Syndrome Edx studies affected by length of nerve, dilution effect 1
wrist Ulnar nerve at the elbow Peroneal (fibular) nerve at the knee Crossed Leg Palsy wrist Ulnar nerve at the elbow Peroneal (fibular) nerve at the knee Tibial nerve at the ankle Tarsal Tunnel Syndrome wrist Ulnar nerve at the elbow Peroneal (fibular) nerve at the knee Tibial nerve at the ankle All sites of potential chronic nerve compression at a site of entrapment How common are entrapment neuropathies? Limited population-based studies Estimate from number of publications Cumulative entrapment neuropathy citations in Medline - 2011 Piriformis syndrome Meralgia paresthetica Peroneal neuropathy Femoral neuropathy Tarsal tunnel syndrome Diagnostic modalities Nerve Conduction and EMG Imaging MRI Ultrasound of nerve and muscle Radial neuropathy Ulnar neuropathy Thoracic outlet syndrome Carpal tunnel syndrome 0 1000 2000 3000 4000 5000 6000 7000 8000 2
Roles for nerve conduction in mononeuropathy/entrapment Localization anatomy Pathophysiology Hallmark is focal slowing, conduction block Demyelination Focal metabolic changes Estimation of severity Reduced/absent CMAPs, SNAPs Combine with needle EMG Fibrillation potentials, MUP enlargement indicate axonal injury How slow is slow? A model of ulnar neuropathy at the elbow Assumptions: Uniform NCV of 60 m/s Focal slowing Area of slowing = 2 cm Distance measurement error of ± 1 cm Stimulate above elbow, below elbow, wrist Calculate above elbow to wrist NCV (AE-W), above elbow to below elbow (AE-BE) NCV Vary NCV in abnormal segment from 1 60 m/s Illustrate dilution effect Above elbow (AE) Below elbow (BE) Wrist (W) How slow is slow? A model of ulnar neuropathy at the elbow Conduction Block Inching study proximal median neuropathy Ulnar NCV Ranges Abnormal Segment NCV AE-W (range), m/s AE-BE (range), m/s 60 50 40 30 25 20 15 10 5 1 60.0 (62.0-58.0) 59.2 (61.2-57.2) 58.1 (60.0-56.1) 56.2 (58.1-54.4) 54.9 (56.7-53.0) 52.9 (54.7-51.2) 50.0 (51.7-48.3) 45.0 (46.5-43.5) 34.6 (35.9-33.5) 12.2 (12.6-11.8) 60.0 (66.0-54.0) 57.7 (63.5-51.9) 54.5 (55.0-45.0) 50.0 (55.0-45.0) 46.9 (51.6-38.6) 42.9 (47.1-38.6) 37.5 (41.2-33.8) 30.0 (33.0-28.0) 18.8 (20.6-16.9) 4.7 (5.2-4.2) Morini, et.al. J Neurol Neurosurg Psychiatry 2000;69:698-699 EMG (needle exam) in mononeuropathy Anatomic distribution of abnormality Fibrillation potentials, positive waves, enlarged MUPs indicate axonal injury Recruitment t (# of MUPs activated) t is an indicator of severity, correlates with strength Assessment of time course acute vs chronic Diagnostic modalities Nerve Conduction and EMG Imaging MRI Ultrasound of nerve and muscle 3
MRI of Nerve Left, A&B MRI at the wrist in normal subject (A T1, B STIR) median nerve is normal size & has normal signal intensity Right, A&B MRI at the wrist in subject with CTS median nerve is enlarged and has increased STIR signal. Note fascicular structure in the enlarged nerve. Grant, et.al. Muscle & Nerve 2002;25:314-331 MRI denervation pattern STIR images of 40 yo man with acute onset fibular neuropathy (A) 2 wks after onset MRC 2/5 of fibular-innervated muscles. No denervation on EMG (B) 8 wks after onset less increased STIR signal. MRC 4/5. Denervation signs on EMG (C) 20 wks after onset normal STIR signal. Strength 5/5, EMG normal Grant, et.al. Muscle & Nerve 2002;25:314-331 Visualization of nerve tumors Malignant Schwannoma of sciatic nerve in 28 yo woman with neurofibromatosis MRI of Nerve Diagnostic modalities Nerve Conduction and EMG Imaging MRI Ultrasound of nerve and muscle Ultrasound in Mononeuropathy Evaluation of superficial nerves Painless Probe orientation Techniques not yet standardized Stand-alone test for diagnosis? Ultrasound in CTS CTS on the left (nerve CSA: 20 mm sq) and normal median nerve on the right (CSA: 11 mm sq) normal <13 Left image is blacker (reduced echogencity) compared to the right. Courtesy F. Walker, MD & M. Cartwright, MD 4
Saggittal view of the median nerve at the wrist the patient is on the left and the normal is on the right note the hour-glass narrowing on the left even at the hourglass, however, this nerve is large compared to the right. For the image on the left, proximal is to the left and on the right proximal is to the right) The median nerve at the distal wrist crease (left image) is compared to the median nerve in the forearm right image both outlined in green note the drop from 20 to 6 mm sq, this ratio should be less than 1.4, not 3.3 Courtesy F. Walker, MD & M. Cartwright, MD Courtesy F. Walker, MD & M. Cartwright, MD What is the pathophysiology? Anatomic correlates Myelin sheath telescoping Nerve enlargement mechanism? Demyelination Wallerian degeneration Conclusion EDX proven value Extensive experience normal vs abnormal well defined Wide availability Painful MRI value not proven cost is an issue Not all radiologists sufficiently experienced Ultrasound emerging technology Not yet standardized, limited availability Supplementary information to EDX Future use as stand-alone instead of EDX or imaging Conclusion EDX proven value Extensive experience normal vs abnormal well defined Wide availability Painful MRI value not proven cost is an issue Not all radiologists sufficiently experienced Ultrasound emerging technology Not yet standardized, limited availability Supplementary information to EDX Future use as stand-alone instead of EDX or imaging Conclusion EDX proven value Extensive experience normal vs abnormal well defined Wide availability Painful MRI value not proven cost is an issue Not all radiologists sufficiently experienced Ultrasound emerging technology Not yet standardized, limited availability Supplementary information to EDX Future use as stand-alone instead of EDX or imaging Modalities likely to be used to provide complementary information 5
6