html5
1 / 30

EMG Blind Spots: mononeuropathies

EMG Blind Spots: mononeuropathies. Anthony Chiodo , MD, MBA University of Michigan Health System AAPMR Meeting, San Diego November, 2014. Clinical syndrome of sensory and/or motor abnormalities in the distribution of a peripheral nerve

fallon-pittman
Download Presentation

EMG Blind Spots: mononeuropathies

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. EMG Blind Spots: mononeuropathies Anthony Chiodo, MD, MBA University of Michigan Health System AAPMR Meeting, San Diego November, 2014

  2. Clinical syndrome of sensory and/or motor abnormalities in the distribution of a peripheral nerve • Does not distinguish neuropraxia, axonotmesis, neurotmesis Mononeuropathy

  3. Radiculopathy • Plexopathy • Myelopathy • Central Etiology • Myofascial pain • Just because patient has a certain constellation of symptoms does not mean that they don’t have a mimicking diagnosis instead Differential Diagnosis of Mononeuropathies

  4. Definitive determiner • Ultimate • Ideal • Reference measurement procedure • Measure of comparison for all other tests of the same problem or disorder Gold Standard

  5. We see patients with classic symptoms with normal studies • We see patients with different symptoms who have abnormal studies • We see patients with symptoms of a different problem who have “superimposed” MN • We see people who we screen with no symptoms with abnormal nerve conduction studies • How useful is clinical presentation as a gold standard? • How useful is physical examination as a gold standard? What is the Gold Standard?

  6. Patients with symptoms that have normal studies • Does the patient have a mimic? • Lengthens the diagnostic evaluation • How far to go in searching for an elusive diagnosis • If not, treat what you think • How far do you treat? • Risk/benefit analysis may be hard to calculate with subjective data only: Who’s the driver??? • Patients without symptoms that have abnormal studies • Can follow over time Blind Spot #1 in Mononeuropathies

  7. Needle examination not commonly helpful • Sensitivity depends on the cut off used • Greater the sensitivity, the lower the specificity • IN OTHER WORDS, GREEN LIGHT FOR SURGICAL TREATMENT • Greater the specificity, the lower the sensitivity • So, just because the nerve conduction studies are normal, does that rule out nerve abnormality as a source of the patient’s complaint? • In general, does not make a good gold standard Trouble with NCS

  8. Sensitivity: TRUE POSITIVE RATE • % Identified with the condition • True positive/(True positive + False negative) • Probability of Positive Test if you do have the condition • Specificity: TRUE NEGATIVE RATE • % identified without the condition • True negative/(True negative + False positive) • Probability of Negative Test if you don’t have the condition Sensitivity and Specificity

  9. 54 presents with one year history of progressive numbness and tingling in the left 1st-3rd digits • Symptoms worse first thing in the morning and with fine motor activities • Notes no weakness • Physical examination: 2+ reflexes, strength 5/5, intact pin sensation, positive Tinel’s, negative Phalen’s Case 1

  10. Normal NCS, SymptomsNormal needle exam, responds to use of carpal tunnel splint

  11. Just because it is highly specific does not mean that all patient’s with abnormal nerve conduction studies have clinical findings consistent with mononeuropathy • 41 year old presents two weeks ago with new onset right sided neck pain and RUE numbness after fall • MRI shows right C5-6 disc herniation • Physical examination: 2+ reflexes, 5/5 strength, non-localizing sensory loss to light touch and pin Highly Specific

  12. Abnormal NCS, No SymptomsNeedle examination is normal

  13. 77 workers with positive NCS but asymptomatic • Auto parts manufacturer, spark plug manufacturer, paper container manufacturer, insurance company • Antidromic median and sensory responses to fingers 2 and 5 at 14 cm • Followed up to 70 months • Previous follow up to 17 months showed no difference between groups • 70% follow up rate • 23% with clinical symptoms of CTS compared to 6% of normal screened (p = 0.01) • Not related to a change in nerve conduction studies!!! • Age, BMI and repetitive work were risk factors Screening to Predict CTSWerner, M+N, 2001.

  14. Increase sensitivity? • Decrease specificity? • Increase sampling error? How many studies do you do?

  15. The greater the error, the less findings are similar to standards • AVOIDING ERRORS MAKES THE BLIND SPOT SMALLER • Common causes of error in NCS • Temperature • Measurement, especially inching • Stimulus intensity How Technique Impacts Your Blind Spot (#2)

  16. In 2014, advanced CT, MRI and ultrasound are all very sensitive tests: Lumbar DDD, rotator cuff syndrome • However, none have proven very specific • Lots of clinically normal patients with very abnormal imaging studies. • So, if the image is abnormal, is it really correlative to the patient’s pain complaint or is it just coincidental? Will Imaging Save Us?

  17. Seven of 14 studies in a critical review • Ulnar studies at the elbow: uses EMG/NCS diagnosis as gold standard. Patients not studied if had symptoms and negative EMG/NCS • Clinical criteria: Weakness of FDP/FCU OR hand intrinsic weakness with sensory changes in the fingers and hand, including DUC Interaction of Ultrasound ImagingBeekman, M+N, 2011.

  18. Ulnar nerve thickening at the elbow: cross-sectional area or transverse diameter • 8.3 to 11 mm2 cut offs • Influence by controls: self, others, both arms in controls • Maximal location • Predetermined locations (2-4) • Swelling ratio • Comparison to cubital tunnel CSA Parameters for Positive Test

  19. Echotexture interpretation • Inner fascicular structure Other nuances

  20. Subluxation • Seen in healthy controls and no systematic comparison • Snapping of the medial head of the triceps • Accessory muscles • See in 11% of cadavers, no systematic comparison • Ganglia • Osteophytes • Tumor Causes

  21. 69 women with symptoms: • Motor weakness or • Positive Flick sign, median hypoesthesia, positive Tinel’s, Phalen’s and reverse Phalen’s • Negative work up for peripheral nerve disease • EMG/NCS: AANEM guidelines • Sensory studies to digits 1,2,3 • Motor studies • Ultrasound (54), CT (39) and MRI (50) • Both hands tested CTS: NCS vs. ImagingDeniz, NS, 2012.

  22. 4 class I articles • Three had clinical findings and abnormal NCS • One had clinical findings and positive response to conservative treatment • Three used opposite side as control if asymptomatic with normal NCS, one used other patients Guideline: Ultrasound in CTSCartwright, Muscle + Nerve, 2012

  23. Class I Study Results

  24. Martin-Gruber Anastomosis • Accessory Fibular (peroneal) Nerve • The All Ulnar Hand Anomalous Innervation: Blind Spot #3

  25. Median to ulnar crossover of ulnar innervated muscles of the hand • Can explain decreased motor evoked amplitude of the ulnar motor response stimulated at the elbow (false conduction block) • Can explain increased motor evoked amplitude of the median motor response stimulated at the elbow Martin-Gruber

  26. Innervate FDIH 21/22 • Innervate Hypothenar 9/22 • Innervate Thenar 3/22 Martin-Gruber: Muscles Affected

  27. Can explain increased motor evoked amplitude of the fibular motor response stimulated at the knee Accessory Fibular Nerve

  28. Questions? Thank you!

More Related