EMG BLIND SPOTS: MONONEUROPATHIES Anthony Chiodo, MD, MBA University of Michigan Health System AAPMR Meeting, San Diego November, 2014

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

Differential Diagnosis of Mononeuropathies 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

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

What is the Gold Standard? 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?

Blind Spot #1 in Mononeuropathies 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

Trouble with NCS 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

Sensitivity and Specificity 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

Case 1 54 presents with one year history of progressive numbness and tingling in the left 1 st -3 rd 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

Normal NCS, Symptoms Normal needle exam, responds to use of carpal tunnel splint Amp: RT Amp : LT Latency: RT Latency: LT CV: RT CT: LT Median Sensory Ulnar sensory Median palm302.3 Ulnar palm252.2 Median motor Ulnar motor

Highly Specific 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

Abnormal NCS, No Symptoms Needle examination is normal Amp : RT Amp: LT Latency : RT Latency: LT CV: RT CV: LT Radial Sensory Forearm322.3 Median Sensory Ulnar Sensory Median Sensory Palm232.4 Ulnar Sensory Palm191.9 Median Motor Wrist Ulnar Motor Wrist

Screening to Predict CTS Werner, M+N, 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

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

How Technique Impacts Your Blind Spot (#2) 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

Will Imaging Save Us? 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?

Interaction of Ultrasound Imaging Beekman, M+N, 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

PatientsControlsSensitivitySpecificity Maximal diameter in 2 locations > CSA 2 locations > NR CSA 3 locations > (B)10093 Diameter Ratio 2720NR CSA 3 locations > Diameter 3 locations 3621 (B)8381 CSA two location and echotexture 3823 (B)5496

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

Other nuances Echotexture interpretation Inner fascicular structure

Causes 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

CTS: NCS vs. Imaging Deniz, NS, 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

SensitivitySpecificity EMG Ultrasound CT MRI6580

Guideline: Ultrasound in CTS Cartwright, Muscle + Nerve, 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

Class I Study Results CTSControlsSensitivitySpecificityArea Improved # # #

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

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

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

QUESTIONS? Thank you!