Correlation between the combined sensory index and clinical outcome after carpal tunnel decompression: a retrospective review.

The combined sensory index (CSI) is a useful electrodiagnostic tool, but it was not known if the CSI can be correlated with clinical outcome following carpal tunnel decompression. The objective of this study was to examine the association between the CSI and symptom relief from pain and parasthesiae following surgical intervention. Retrospective chart review was performed on 272 patients, diagnosed with carpal tunnel syndrome by electrodiagnostic criteria, who proceeded to undergo open or endoscopic carpal tunnel release with postoperative follow-up at an academic medical center between 1996 and 2006. The CSI demonstrated statistical significance (P = 0.03) for correlation with resolution of pain and parasthesiae following carpal tunnel decompression. Patients with a CSI of 2.5-4.6 had the best prognosis for resolution of pain and parasthesiae following surgical intervention. Median compound muscle action potential (CMAP) amplitude and median motor latency were also associated with resolution of parasthesiae, but not pain. The CSI effectively establishes correlation with clinical outcomes following surgical intervention for carpal tunnel syndrome, and thus a range of optimal outcomes (CSI between 2.5 and 4.6) can also be established.

Does stimulus rate matter when performing somatosensory evoked potentials for coma patients?

INTRODUCTION: It is unclear whether the rate of stimulation for somatosensory evoked potentials (SEPs) can influence the presence or absence of cortical responses to median nerve stimulation in comatose patients. If so, this could affect how SEPs are performed and interpreted for prognostication in coma. Our objective was to determine how frequently our comatose patients had absent median nerve SEP responses at 3 Hz stimulation, but present responses at 1 Hz stimulation, and to report outcomes of these patients. METHODS: We reviewed SEP recordings in 639 comatose patients over a 9-year period. All had stimulation at 3 Hz and 1 Hz. This is a retrospective review. RESULTS: There were seven patients who had absent median nerve SEP responses at 3 Hz stimulation bilaterally, but had present responses at 1 Hz on one or both sides. Six of the seven died. One 16-year-old patient with traumatic brain injury awoke, but had moderate disability. CONCLUSIONS: Stimulation rate is an important determinant of presence or absence of cortical responses in about 1% of comatose patients. It is unclear whether such patients have a different outcome that those with absent responses at both rates of stimulation.

Reliability in interpretation of median somatosensory evoked potentials in the setting of coma: factors and implications.

BACKGROUND: Median nerve short-latency somatosensory evoked potentials (SSEPs) are useful in determining prognosis for awakening after coma following hypoxic ischemic encephalopathy, but reliability of interpretation is unclear. OBJECTIVE: To measure inter- and intra-observer reliability of determining presence or absence of SSEPs in comatose patients following hypoxic ischemic encephalopathy and to identify factors that enhance reliability. DESIGN: Retrospective review by four readers (experience ranging from 2-27 years) of SSEP recordings in 95 comatose patients. Twenty waveforms were presented twice and five waveforms were presented pre- and post-neuromuscular junction (NMJ) blockade. SETTING: Academic teaching hospital and level 1 trauma center. PATIENTS: Inpatients in coma due to hypoxic ischemic encephalopathy. MEASUREMENTS AND MAIN RESULTS: Kappa values among the four readers, reflecting inter-observer reliability, ranged from 0.39 to 0.79 (mean 0.60, SD 0.16), a level of agreement interpreted as "moderate." Better inter-observer reliability was seen when: cortical amplitudes were ≥ 0.7 µV, baseline noise was smaller, and when experience level between reviewers was most similar. In cases examined both pre- and post-NMJ blockade, average kappa values of inter-observer reliability increased significantly from 0.03 pre-NMJ blockade to 0.41 post-NMJ blockade. Intra-observer reliability was higher than that for inter-observer, with a "substantial" average kappa of 0.84 (range 0.79-0.89, SD .06). CONCLUSIONS: Inter- and intra-observer reliability of SSEP interpretation in comatose patients varies from moderate to substantial, respectively. In order to reliably interpret the presence of small cortical responses, NMJ blockade should be used when baseline noise is excessive.

Somatosensory evoked potentials in coma prognosis.

SEPs provide useful prognostic information regarding outcome after coma. Use of the summary data presented here should allow clinicians caring for these patients to provide families with a greater degree of certainty regarding outcome than previously has been available.

Predicting recovery after fibular nerve injury: which electrodiagnostic features are most useful?

OBJECTIVE: Although it is important to have strong predictors of outcome in peripheral mononeuropathies so that appropriate management can be instituted early, little is known about the prognostic value of electrodiagnostic results for these lesions. Our objective in this study was to evaluate the prognostic value of electrodiagnostic studies in fibular neuropathy. DESIGN: In this retrospective study, 39 of 138 subjects with fibular neuropathy met the inclusion criteria. Electrodiagnostic results at the time of testing were evaluated for their value in predicting outcome. Good outcome was defined as grade 4 or higher strength on the Medical Research Council Scale in ankle dorsiflexion. RESULTS: Compound muscle action potential responses from extensor digitorum brevis and tibialis anterior predicted prognosis: 81% of subjects with any tibialis anterior response and 94% with any extensor digitorum brevis response had a good outcome vs. those with absent responses (46% and 52%, respectively). Importantly, there was still a high likelihood of good outcome with absent compound muscle action potential responses. Tibialis anterior compound muscle action potential gave additional prognostic information when extensor digitorum brevis response was absent. Recruitment in tibialis anterior was predictive in traumatic cases. All patients with nontraumatic compression had a good outcome. CONCLUSIONS: We conclude that electrodiagnostic studies produce useful prognostic information in fibular neuropathy, particularly in traumatic cases.

Association between the EMG self-assessment examination and later ABEM certification.

Our objective was to determine whether performance on the American Association of Neuromuscular and Electrodiagnostic Medicine Training Program Self-Assessment Examination (TPSAE) predicts subsequent performance on the American Board of Electrodiagnostic Medicine (ABEM) certification examination. The TPSAE results were closely associated (r = 0.57) with ranking on the ABEM examination. Those with scores <65% on the TPSAE had <50% chance of ABEM certification, whereas those with scores >84% correct had >90% chance of certification. The TPSAE is a useful predictor of later ABEM certification.

Prognostic values of electrodiagnostic studies in traumatic radial neuropathy.

It is important to have strong predictors of outcome in traumatic neuropathies so that appropriate management can be instituted early. Our objective in this study was to evaluate the prognostic value of electrodiagnostic studies in traumatic radial neuropathy. In this retrospective study, 33 of 67 subjects with traumatic radial neuropathy met the inclusion criteria. Good outcome was defined as grade 3 or higher strength on the Medical Research Council scale in wrist extensors. Compound muscle action potential (CMAP) responses from extensor indicis proprius (EIP) predicted prognosis: 92% of subjects with a recordable CMAP had a good outcome; and 65% of those with an absent response had a good outcome. Recruitment in brachioradialis was also predictive: 92% of those with full, central, or reduced recruitment had a good outcome; 67% of those with discrete recruitment had a good outcome; and only 33% of those with absent recruitment had a good outcome. Studies performed more than 3 months after injury produced more prognostic certainty than those performed earlier. We conclude that electrodiagnostic studies produce useful prognostic information in traumatic radial neuropathy. It is noteworthy, however, that 65% of subjects with an absent radial CMAP (suggesting complete or nearly complete axon loss) still have a good outcome.

Which motor nerve conduction study is best in ulnar neuropathy at the elbow?

There is debate regarding how best to utilize ulnar motor nerve conduction velocity (MNCV) to identify ulnar neuropathy at the elbow (UNE). We used receiver operator characteristic (ROC) curves to compare absolute across-elbow MNCV with MNCV difference between elbow and forearm segments (VDIF) when recording from abductor digiti minimi (ADM) and first dorsal interosseous (FDI) muscles. Also, we determined how their utility was impacted by low amplitudes of compound muscle action potentials (CMAPs). We studied 85 subjects with UNE and 77 subjects with carpal tunnel syndrome but without clinical evidence of UNE. The UNE group was divided into three subgroups based on CMAP amplitude. At 95% specificity, MNCV sensitivities were 80% at ADM and 77% at FDI, and VDIF sensitivities were 51% at ADM and 38% at FDI. The ROC curves showed MNCV to be superior to VDIF across all amplitude subgroups; however, confidence intervals overlapped when amplitude was high.

Clinical utility of the flick maneuver in diagnosing carpal tunnel syndrome.

OBJECTIVE: To determine the utility of the flick maneuver (flicking motion of hands and wrists when most symptomatic) in the clinical evaluation of carpal tunnel syndrome (CTS). DESIGN: Review of standardized data collection on 142 subjects referred for electrodiagnostic evaluation of possible CTS at a university hospital electrodiagnostic clinic. Subjects were first clinically evaluated with the flick, Phalen, and Tinel maneuvers. Subsequently, they all underwent nerve conduction studies. Electrodiagnostic results were used as the gold standard for patient group assignments. Sensitivities, specificities, and predictive values for individual and combined clinical tests were determined. McNemar chi square values were calculated to determine whether one test identified more patients with CTS. The sensitivities of clinical maneuvers were also evaluated in relation to electrodiagnostic severity of CTS. RESULTS: Of the 142 subjects, 67% had CTS. The sensitivities of the flick, Tinel, and Phalen signs were 37%, 27%, and 34%, respectively. False-positive results ranged from 8% (Tinel) to 26% (flick and Phalen). Positive predictive values for the flick, Tinel, and Phalen maneuvers were 74%, 87%, and 73%, respectively, and negative predictive values were 37%, 39%, and 35%. McNemar chi square results revealed that the flick maneuver detected more subjects with CTS than the Tinel sign. With increasing electrodiagnostic severity, the sensitivity of all clinical tests tended to improve slightly. CONCLUSION: The flick sign is of limited clinical utility in diagnosing CTS, with low sensitivity and specificity.

Predictive value of somatosensory evoked potentials for awakening from coma.

OBJECTIVES: A systematic review of somatosensory evoked potentials performed early after onset of coma, to predict the likelihood of nonawakening. The pooled results were evaluated for rates of awakening, confidence intervals, and the possibility of rare exceptions. DATA SOURCES: Forty-one articles reporting somatosensory evoked potentials in comatose patients and subsequent outcomes, from 1983 to 2000. STUDY SELECTION: Studies were included if they reported coma etiology, age group, presence or absence of somatosensory evoked potentials, and coma outcomes. DATA EXTRACTION: We separated patients into four groups: adults with hypoxic-ischemic encephalopathy, adults with intracranial hemorrhage, adults and adolescents with traumatic brain injury, and children and adolescents with any etiologies. Somatosensory evoked potentials were categorized as normal, abnormal, or bilaterally absent. Outcomes were categorized as persistent vegetative state or death vs. awakening. DATA SYNTHESIS: For each somatosensory evoked potential result, rates of awakening (95% confidence interval) were calculated: adult hypoxic-ischemic encephalopathy: absent 0% (0%-1%), abnormal 22% (17%-26%), normal 52% (48%-56%); adult intracranial hemorrhage: absent 1% (0%-4%), present 38% (27%-48%); adult-teen traumatic brain injury: absent 5% (2%-7%), abnormal 70% (64%-75%), normal 89% (85%-92%); child-teen: absent 7% (4%-10%), abnormal 69% (61%-77%), normal 86% (80%-92%). CONCLUSIONS: Somatosensory evoked potential results predict the likelihood of nonawakening from coma with a high level of certainty. Adults in coma from hypoxic-ischemic encephalopathy with absent somatosensory evoked potential responses have <1% chance of awakening.