Compound Muscle Action Potential Duration Research Articles

New Measurement in the Diagnosis of Critical Illness Myopathy: Stimulus Intensity and Compound Muscle Action Potential Duration Relationship (P1-11.013)

New Measurement in the Diagnosis of Critical Illness Myopathy: Stimulus Intensity and Compound Muscle Action Potential Duration Relationship (P1-11.013)

Compound Muscle Action Potential (CMAP) Duration and Myosin Loss in Patients with Critical Illness Myopathy: Correlation and Prognostication (P1-11.005)

Compound Muscle Action Potential (CMAP) Duration and Myosin Loss in Patients with Critical Illness Myopathy: Correlation and Prognostication (P1-11.005)

Pathologic classification of a late-onset peripheral neuropathy in a spontaneous Labrador retriever dog model.

Late-onset peripheral neuropathy (LPN) is a heritable canine neuropathy commonly found in Labrador retrievers and is characterized by laryngeal paralysis and pelvic limb paresis. Our objective was to establish canine LPN as a model for human hereditary peripheral neuropathy by classifying it as either an axonopathy or myelinopathy and evaluating length-dependent degeneration. We conducted a motor nerve conduction study of the sciatic and ulnar nerves, electromyography (EMG) of appendicular and epaxial musculature, and histologic analysis of sciatic and recurrent laryngeal nerves in LPN-affected and control dogs. LPN-affected dogs exhibited significant decreases in compound muscle action potential (CMAP) amplitude, CMAP area, and pelvic limb latencies. However, no differences were found in motor nerve conduction velocity, residual latencies, or CMAP duration. Distal limb musculature showed greater EMG changes in LPN-affected dogs. Histologically, LPN-affected dogs exhibited a reduction in the number of large-diameter axons, especially in distal nerve regions. In conclusion, LPN in Labrador retrievers is a common, spontaneous, length-dependent peripheral axonopathy that is a novel animal model of age-related peripheral neuropathy that could be used for fundamental research and clinical trials.

Electromyographic predictors of abducens nerve palsy after endoscopic skull base surgery.

Recovery of abducens nerve palsy (ANP) after endoscopic endonasal skull base surgery (ESBS) has been shown to be potentially predicted by postoperative ophthalmological examination. Triggered electromyography (t-EMG) and free-run electromyography (f-EMG) activity provide an intraoperative assessment of abducens nerve function, but associations with long-term ANP outcomes have not been explored. The objective of this study was to describe intraoperative abducens EMG characteristics and determine whether these electrophysiological profiles are associated with immediately postoperative and long-term ANP outcomes after ESBS. The authors conducted a 5-year (2011-2016) retrospective case-control study of patients who underwent ESBS in whom the abducens nerve was stimulated (t-EMG). Electrophysiological metrics were compared between patients with a new postoperative ANP (cases) and those without ANP (controls). Pathologies included chordoma, pituitary adenoma, meningioma, cholesterol granuloma, and chondrosarcoma. Electrophysiological data included the presence of abnormal f-EMG activity, t-EMG stimulation voltage, stimulation threshold, evoked compound muscle action potential (CMAP) amplitude, onset latency, peak latency, and CMAP duration at various stages of the dissection. Controls were selected such that pathologies were similarly distributed between cases and controls. Fifty-six patients were included, 26 with new postoperative ANP and 30 controls without ANP. Abnormal f-EMG activity (28.0% vs 3.3%, p = 0.02) and lack of response to stimulation (27% vs 0%, p = 0.006) were more frequent in patients with immediately postoperative ANP than in controls. Patients with immediately postoperative ANP also had a lower median CMAP amplitude (35.0 vs 71.2 μV, p = 0.02) and longer onset latency (5.2 vs 2.8 msec, p = 0.04). Comparing patients with transient versus persistent ANP on follow-up, those with persistent ANP tended to have a lower CMAP amplitude (12.8 vs 57 μV, p = 0.07) and higher likelihood of not responding to stimulation at the end of the case (45.5% vs 7.1%, p = 0.06). Abnormal f-EMG was not associated with long-term ANP outcomes. The presence of f-EMG activity, lack of CMAP response to stimulation, decreased CMAP amplitude, and increased CMAP onset latency were associated with immediately postoperative ANP. Long-term ANP outcomes may be associated with t-EMG parameters, including whether the nerve is able to be stimulated once identified and CMAP amplitude. Future prospective studies may be designed to standardize abducens nerve electrophysiological monitoring protocols to further refine operative and prognostic utility.

Cdon ablation in motor neurons causes age-related motor neuron degeneration and impaired sciatic nerve repair.

The functional deterioration and loss of motor neurons are tightly associated with degenerative motor neuron diseases and aging-related muscle wasting. Motor neuron diseases or aging-related muscle wasting in turn contribute to increased risk of adverse health outcomes in the elderly. Cdon (cell adhesion molecule-downregulated oncogene) belongs to the immunoglobulin superfamily of cell adhesion molecule and plays essential roles in multiple signalling pathways, including sonic hedgehog (Shh), netrin, and cadherin-mediated signalling. Cdon as a Shh coreceptor plays a critical role in motor neuron specification during embryonic development. However, its role in adult motor neuron function is unknown. Hb9-Cre recombinase-driven motor neuron-specific Cdon deficient mice (mnKO) and a compound mutant mice (mnKO::SOD1G93A ) were generated to investigate the role of Cdon in motor neuron degeneration. Motor neuron regeneration was examined by using a sciatic nerve crush injury model. To investigate the phenotype, physical activity, compound muscle action potential, immunostaining, and transmission electron microscopy were carried out. In the mechanism study, RNA sequencing and RNA/protein analyses were employed. Mice lacking Cdon in motor neurons exhibited middle age onset lethality and aging-related decline in motor function. In the sciatic nerve crush injury model, mnKO mice exhibited an impairment in motor function recovery evident by prolonged compound muscle action potential duration (4.63±0.35 vs. 3.93±0.22s for f/f, P<0.01) and physical activity. Consistently, neuromuscular junctions of mnKO muscles were incompletely occupied (49.79±5.74 vs. 79.39±3.77% fully occupied neuromuscular junctions for f/f, P<0.0001), suggesting an impaired reinnervation. The transmission electron microscopy analysis revealed that mnKO sciatic nerves had smaller axon diameter (0.88±0.13 vs. 1.43±0.48μm for f/f, P<0.0001) and myelination defects. RNA sequencing of mnKO lumbar spinal cords showed alteration in genes related to neurogenesis, inflammation and cell death. Among the altered genes, ErbB4 and FgfR expressions were significantly altered in mnKO as well as in Cdon-depleted NSC34 motor neuron cells. Consistently, Cdon-depleted NSC34 cells exhibited elevated levels of cleaved Caspase3 and γH2AX proteins, as well as Bax transcription. Cdon-depleted NSC34 cells also exhibited impaired activation of Akt in response to neuregulin-1 (NRG1) treatment. Our current data demonstrate the functional importance of Cdon in motor neuron function and nerve repair. Cdon ablation causes alterations in neurotrophin signalling that leads to motor neuron degeneration.

Markedly prolonged compound muscle action potential duration in a patient with coronavirus disease 2019 related critical illness myopathy

AbstractA 56‐year‐old man admitted with coronavirus disease 2019 (COVID‐19) became severely ill, required ventilator support and intensive care unit management. After ventilator weaning, he was found to have quadriparesis. Guillain–Barré syndrome (GBS) was suspected and administration of high‐dose intravenous immunoglobulin (IVIg) was considered. However, markedly prolonged compound muscle action potential (CMAP) duration was observed, leading to a diagnosis of critical illness myopathy (CIM). Therefore, IVIg was not given at all, and supportive care was continued. A good functional recovery was obtained. Prolonged CMAP duration is a characteristic finding to CIM. CIM following severe COVID‐19 infection is probably common, although the diagnostic value of prolonged CMAP duration is not widely recognized. This characteristic finding deserves more attention because it contributes to early differentiation between CIM and GBS and the use of IVIg in patients with COVID‐19 may cause thrombotic complications and worsen the prognosis.

Compound muscle action potential duration ratio for differentiation between Charcot-Marie-Tooth disease and CIDP

ObjectiveTo elucidate the utility of the proximal to distal compound muscle action potential (CMAP) duration ratio to distinguish between demyelinating Charcot-Marie-Tooth disease (CMT) and chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) compared with nerve ultrasound. MethodsThirty-nine demyelinating CMT patients and 19 CIDP patients underwent nerve conduction studies (NCS) and nerve ultrasound. NCS parameters including CMAP duration ratio calculated by dividing the value at the proximal site by that at the distal site and nerve cross-sectional area (CSA) measured by ultrasound were compared between the two groups. The diagnostic sensitivity and specificity of each parameter were analysed. ResultsCMT patients showed a significantly lower CMAP duration ratio than CIDP patients (p < 0.05). The area under the curve (AUC) value of the CMAP duration ratio exceeded 0.95 when CMT was considered “positive”, and a cut-off value of 1.13 resulted in high diagnostic sensitivity and specificity (84.6 and 100 % for median nerve, 97.4 and 85.7 % for ulnar nerve, respectively), whereas the AUC value of nerve CSA ranged from 0.70 to 0.81. ConclusionsThe CMAP duration ratio could effectively distinguish between demyelinating CMT and CIDP. SignificanceAdding the CMAP duration ratio to a routine NCS may improve the accuracy of the diagnosis of demyelinating CMT.

Multimodal assessment of intensive care unit-acquired weakness in severe stroke patients.

Intensive care unit-acquired weakness (ICUAW) defines generalized muscle weakness seen in critically ill patients in the absence of other causative factors. Herein, we aimed to evaluate ICUAW in stroke patients by electrodiagnostic testing, histopathology, and assessment of respiratory complex activities (RCA), to define the frequency of ICUAW in this patient group, and to reach new parameters for early prediction and diagnosis. We prospectively recruited twenty-four severe acute stroke patients during a sixteen-month period. In addition to serial nerve conduction studies (NCS), we performed muscle biopsy and RCA analysis on the non-paretic side when ICUAW developed. Patients undergoing orthopedic surgery without metabolic and neuromuscular diseases constituted the control group for RCA. Survival and longitudinal data were analyzed by joint modeling to determine the relationship between electrophysiological parameters and ICUAW diagnosis. Eight patients (33%) developed ICUAW, and six of them within the first two weeks. Extensor digitorum brevis, abductor digiti minimi (ADM), rectus femoris and vastus medialis (VM) compound muscle action potential (CMAP) amplitudes showed a significant decrease in the ICUAW group. VM CMAP amplitude (BIC = 358.1574) and ADM CMAP duration (BIC = 361.1028) were the best-correlated parameters with ICUAW diagnosis. The most informative electrophysiological findings during the entire study were obtained within the first 11days. Muscle biopsies revealed varying degrees of type 2 fiber atrophy. Complex I (p = 0.003) and IV (p = 0.018) activities decreased in patients with ICUAW compared to controls. VM CMAP amplitude and ADM CMAP duration correlate well with ICUAW diagnosis, and may aid in the early diagnosis.

Temporal Dispersion and Duration of the Distal Compound Muscle Action Potential Do Not Distinguish Diabetic Sensorimotor Polyneuropathy From Chronic Inflammatory Demyelinating Polyneuropathy.

ObjectiveTo investigate the contribution of duration and temporal dispersion (TD) of the distal compound muscle action potential (CMAP) in discriminating chronic inflammatory demyelinating polyneuropathy (CIDP) from diabetic sensorimotor polyneuropathy (DSP) and from CIDP+DSP.MethodsWe performed a retrospective review of patients diagnosed with CIDP, DSP and CIDP+DSP (responsive to immunotherapy) and examined differences in CMAP duration and TD at baseline.ResultsWe included 59 subjects: 17 CIDP, 21 DSP and 21 CIDP+DSP. Of these, 16 (94.1%) CIDP, 18 (85.7%) CIDP+DSP and 1 (4.7%) DSP fulfilled the 2010 EFNS/PNS criteria for definite CIDP. There was no difference in CMAP duration or TD in all nerves (compound outcome) or in individual motor nerves. Patients with CIDP/CIDP+DSP had more conduction blocks, slower conduction velocities and more prolonged F wave latencies than those with DSP.ConclusionMeasures of CMAP duration and TD were not helpful in distinguishing CIDP, DSP or CIDP+DSP patients; however, parameters such as F-wave latencies, conduction blocks or the number of demyelinating parameters were useful in this separation.SignificanceThere are no definite nerve conduction criteria to distinguish patients with CIDP+DSP from DSP alone. Further studies focusing on measures of demyelination may provide stronger evidence to guide treatment decisions in CIDP + DSP patients.

F wave in restless legs syndrome, as an electrophysiological response of clinical relief

ABSTRACT Objective The study aimed to evaluate the impact of postural changes on the F wave-related parameters and whether those changes were associated with clinical relaxation, which was achieved in restless legs syndrome patients with standing up. Methods F wave duration (FWD), compound muscle action potential duration (CMAPD), and FWD/CMAPD ratio were evaluated in supine and upward positions in 18 restless legs syndrome patients and compared with 18 age and gender-matched healthy volunteers. Results FWD/CMAPD was significantly higher for the tibial nerve at supine position (p = 0.043) but not at upright position (p = 0.206) and for ulnar nerve, both at supine (p = 0.007) and upright positions (p = 0.023) in RLS patients compared to controls. Ulnar FWD decreased significantly at the upright position in both control and RLS patients (p = 0.035, p = 0.028, respectively). CMAPD decreased only in the control group with standing up for both ulnar and tibial nerves (p = 0.048, p = 0.017, respectively). Discussion Ulnar and tibial FWD/CMAPD ratios increased in RLS patients compared to controls. However, FWD/CMAPD was not affected by the posture within the groups. Postural change seems to be a factor that decreased ulnar FWD both in RLS patients and the control group. Ulnar and tibial CMAPD reduced only in healthy controls with an upright position. Tibial and ulnar FWD/CMAPD ratios are favorable electrophysiological parameters diagnosing RLS. The tibial FWD/CMAPD ratio loses its significance only when the patient stands up, reflecting the clinical relief achieved with the postural change.

Comparison of second lumbrical interosseous median and ulnar motor conduction study in population of subjects with idiopathic carpal tunnel syndrome and non-CTS hands-a cross-sectional study

Background: Second lumbrical interosseous (2L-I) median-ulnar motor conduction study across wrist is pivotal in electrodiagnosis of carpal tunnel syndrome (CTS) in different grades of severity. 2L-I Median versus ulnar distal motor latency (DML) difference more than 0.5 milliseconds is used to diagnose median neuropathy at wrist. Other variables of study, namely, 2L DML, compound muscle action potential (CMAP) amplitude, CMAP duration, and conduction velocity (CV) remain less explored with few studies pressing for its role to substantiate CTS diagnosis. Aims and Objectives: Current cross-sectional study aimed to explore role of 2L-I DML, amplitude, duration, and CV in diagnosis of median neuropathy at wrist. Materials and Methods: Total 70, 37 clinically suspected CTS hands and 33 age, height, and weight matched non-CTS hands underwent 2L-I Median Ulnar motor conduction study. Results: Statistically significant difference (P &lt; 0.05) in 2L median DML, CMAP amplitude, duration and CV between CTS and non-CTS hands along with 2L-I Median versus Ulnar DML difference. 2L DML and 2L-I DML difference variables showed better specificity and sensitivity: 83.78 and 93.91, respectively, in diagnosing CTS. Conclusion: We concluded that apart from 2L-I DML difference other variables such as DML, amplitude, duration, and CV may also play substantial role in evaluation of CTS and may be included as part of electrodiagnostic protocol.

Duration and temporal dispersion measurements in CIDP subjects from the Polyneuropathy And Treatment with Hizentra (PATH) study

Abstract:&#x0D; Introduction: Distal compound muscle action potential (dCMAP) duration and temporal dispersion (TD) are electrophysiological hallmarks of demyelination and important for the diagnosis of CIDP. While the impact of CIDP treatment on other nerve conduction parameters has been examined, the effects on dCMAP and TD remain unexplored. The aim of the study was to examine the impact of withdrawal of immunoglobulin treatment on dCMAP duration and TD, and also the influence of the measurement technique on dCMAP duration and TD.&#x0D; Methods: Nerve conduction studies were analyzed from the PATH (Polyneuropathy And Treatment with Hizentra) study which randomized patients with CIDP to two doses of IgPro 20 and placebo. Distal CMAP duration and TD were obtained by two methods of measurements (D1 and D2, TD1 and TD2) from the median and peroneal nerves. &#x0D; Results: The dCMAP and TD were obtained from 389 tracings. While the two methods of measurement showed differences in D1 and D2 with D2 longer than D1 in all the three groups, there was no difference between the TD1 and TD2. There was no difference at baseline in dCMAP duration or TD among the three groups. At the end of treatment, patients in the placebo arm had no worsening of dCMAP and TD compared to baseline or the treated groups.&#x0D; Conclusion: dCMAP duration and TD did not show a difference between treated and placebo groups, and may be less sensitive measures than other nerve conduction parameters when evaluating changes in treatment. The method of dCMAP duration measurement does not affect TD as long as a consistent method is followed.&#x0D;

Neurogenic vs. Myogenic Origin of Acquired Muscle Paralysis in Intensive Care Unit (ICU) Patients: Evaluation of Different Diagnostic Methods.

Introduction. The acquired muscle paralysis associated with modern critical care can be of neurogenic or myogenic origin, yet the distinction between these origins is hampered by the precision of current diagnostic methods. This has resulted in the pooling of all acquired muscle paralyses, independent of their origin, into the term Intensive Care Unit Acquired Muscle Weakness (ICUAW). This is unfortunate since the acquired neuropathy (critical illness polyneuropathy, CIP) has a slower recovery than the myopathy (critical illness myopathy, CIM); therapies need to target underlying mechanisms and every patient deserves as accurate a diagnosis as possible. This study aims at evaluating different diagnostic methods in the diagnosis of CIP and CIM in critically ill, immobilized and mechanically ventilated intensive care unit (ICU) patients. Methods. ICU patients with acquired quadriplegia in response to critical care were included in the study. A total of 142 patients were examined with routine electrophysiological methods, together with biochemical analyses of myosin:actin (M:A) ratios of muscle biopsies. In addition, comparisons of evoked electromyographic (EMG) responses in direct vs. indirect muscle stimulation and histopathological analyses of muscle biopsies were performed in a subset of the patients. Results. ICU patients with quadriplegia were stratified into five groups based on the hallmark of CIM, i.e., preferential myosin loss (myosin:actin ratio, M:A) and classified as severe (M:A < 0.5; n = 12), moderate (0.5 ≤ M:A < 1; n = 40), mildly moderate (1 ≤ M:A < 1.5; n = 49), mild (1.5 ≤ M:A < 1.7; n = 24) and normal (1.7 ≤ M:A; n = 19). Identical M:A ratios were obtained in the small (4–15 mg) muscle samples, using a disposable semiautomatic microbiopsy needle instrument, and the larger (>80 mg) samples, obtained with a conchotome instrument. Compound muscle action potential (CMAP) duration was increased and amplitude decreased in patients with preferential myosin loss, but deviations from this relationship were observed in numerous patients, resulting in only weak correlations between CMAP properties and M:A. Advanced electrophysiological methods measuring refractoriness and comparing CMAP amplitude after indirect nerve vs. direct muscle stimulation are time consuming and did not increase precision compared with conventional electrophysiological measurements in the diagnosis of CIM. Low CMAP amplitude upon indirect vs. direct stimulation strongly suggest a neurogenic lesion, i.e., CIP, but this was rarely observed among the patients in this study. Histopathological diagnosis of CIM/CIP based on enzyme histochemical mATPase stainings were hampered by poor quantitative precision of myosin loss and the impact of pathological findings unrelated to acute quadriplegia. Conclusion. Conventional electrophysiological methods are valuable in identifying the peripheral origin of quadriplegia in ICU patients, but do not reliably separate between neurogenic vs. myogenic origins of paralysis. The hallmark of CIM, preferential myosin loss, can be reliably evaluated in the small samples obtained with the microbiopsy instrument. The major advantage of this method is that it is less invasive than conventional muscle biopsies, reducing the risk of bleeding in ICU patients, who are frequently receiving anticoagulant treatment, and it can be repeated multiple times during follow up for monitoring purposes.

Electrodiagnostic data-driven clustering identifies a prognostically different subgroup of patients with chronic inflammatory demyelinating polyneuropathy

ObjectiveThis study aimed to explore the correlations between electrodiagnostic (EDX) features in patients with chronic inflammatory demyelinating polyneuropathy (CIDP) and to investigate whether EDX data-driven clustering can identify a distinct...

Electrophysiological demyelinating features in hereditary ATTR amyloidosis

Objective: To elucidate the electrophysiological demyelinating features in patients with hereditary ATTR amyloidosis that may lead to a misdiagnosis of chronic inflammatory demyelinating polyneuropathy (CIDP).Methods: In 102 patients with hereditary ATTR amyloidosis (85 Val30Met and 17 non-Val30Met; 37 and 65 from endemic and non-endemic areas, respectively), results of motor nerve conduction studies (MNCSs) with a 2-Hz low-cut filter in the unilateral ulnar and tibial nerves were retrospectively investigated to assess whether each MNCS parameter demonstrated demyelinating features that fulfil the European Federation of Neurological Societies/Peripheral Nerve Society electrodiagnostic (EFNS/PNS EDX) criteria for CIDP.Results: Thirteen patients with low compound muscle action potential (CMAP) amplitude in the tibial nerve (0.7 ± 0.7 mV) and prolonged distal CMAP duration in the ulnar nerve satisfied the definite EFNS/PNS EDX criteria for CIDP. Abnormal temporal dispersion and prolongation of distal latency in the tibial nerve were observed in 5 of 13 patients. However, only one of the 13 patients presented with the reduction of motor conduction velocity in each nerve. No patient exhibited conduction block in any nerve.Conclusion: Patients with hereditary ATTR amyloidosis occasionally show electrophysiological demyelinating features without conduction block following severe axonal degeneration.

F101. Effect of gender on nerve conduction studies parameters in healthy individuals

Introduction Nerve conduction studies (NCS) are electrodiagnostic tests which are used to evaluate the ability of the conduction of the motor and sensory nerves. Nerve conduction studies assist in the evaluation of neuromuscular diseases by providing a physiologic assessment of the peripheral nerve, muscle, neuromuscular junction, dorsal root ganglion cell and anterior horn cell. Among the various factors affecting nerve conduction gender has effect on latency, amplitude and conduction velocity of motor and sensory nerves. Methods The study was conducted on 50 (m = 25; f = 25) age matched healthy individuals of 18–24 age group. The compound muscle action potential (CMAP) and sensory nerve action potential (SNAP) were recorded in Department of Physiology, Kathmandu University School of Medical Sciences. Results Males had higher CMAP amplitude, longer latencies and duration. SNAP latencies and duration were longer in males whereas amplitude was higher in females. Conclusion Gender has definite effects on NCS variables and the effects are not similar in motor and sensory nerves.

P335 Comparison of median nerve distal motor responses in patients with chronic inflammatory demyelinating polyneuropathy and carpal tunnel syndrome

Objective Dispersion of distal compound muscle action potential (CMAP) is a useful finding for showing demyelination. In this study, we aimed to compare the duration and area of CMAP of median nerve between cases with Chronic Inflammatory Demyelinating Polyneuropathy (CIDP) and Carpal Tunnel Syndrome (CTS). Material and methods Ninety-two participants (thirty patients with CDIP, 32 patients with CTS and 30 participants of normal control group) who were evaluated. The CMAP duration was measured from the onset of the initial negative potential to the terminal negative deflection back to baseline. The CMAP area calculation was performed by computerized EMG machine. Results A significant difference was not found between groups as for mean age of the groups, and distribution of genders (CIDP: 52,73 ± 12,34 years, 18 (%40) women, 12 (%60) men; CTS: 52,38 ± 11,83 years, 25 (%78,1) women, 7 (%21,9) men; control: 48,5 ± 14,41 years,22 (%79,3) women, and 8 (%26,7) men). The mean CMAP duration of patients with CIDP was significantly higher than patients with CTS (p: 0.003) and control group (p: 0.001), however there was not any significant difference between the patients with CTS and control group (p > 0.05). The mean CMAP area of patients with CIDP was significantly lower than patients with CTS (p: 0.003) and control group (p: 0.001), however there was not any significant difference between the patients with CTS and control group (p > 0.05). Conclusion These findings suggest that the duration and area of distal CMAP is a useful parameter for the differentiation of patients with CIDPand CTS.

Compound muscle action potential duration in critical illness neuromyopathy.

We sought to determine the specificity of compound muscle action potential (CMAP) durations and amplitudes in a large critical illness neuromyopathy (CINM) cohort relative to controls with other neuromuscular conditions. Fifty-eight patients with CINM who had been seen over a 17-year period were retrospectively studied. Electrodiagnostic findings of the CINM cohort were compared with patients with axonal peripheral neuropathy and myopathy due to other causes. Mean CMAP durations were prolonged, and mean CMAP amplitudes were severely reduced both proximally and distally in all nerves studied in the CINM cohort relative to the control groups. The specificity of prolonged CMAP durations for CINM approached 100% if they were encountered in more than 1 nerve. Prolonged, low-amplitude CMAPs occur more frequently and with greater severity in CINM patients than in neuromuscular controls with myopathy and axonal neuropathy and are highly specific for the diagnosis of CINM. Muscle Nerve 57: 395-400, 2018.

3-2-07. Clinical application of the measurement of muscle fiber conduction velocity using direct muscle stimulation for critical illness myopathy (CIM)

Measurement of the muscle fiber conduction velocity (MFCV) using direct muscle stimulation has been considered to be useful for the evaluation of critical illness myopathy (CIM), although there are rather few reports on this issue. Subjects consisted of 2 normal volunteers, 4 patients with myositis, and 1 patient with CIM. Stimulation was given to the muscle using a monopolar needle and the muscle fiber action potentials (MFAPs) was recorded using a concentric needle electrode. MFCV was calculated based on the onset latencies of the MFAPs recorded at different intramuscular locations. As results, MFCV was 4–5 m/s in the CIM patient. It was 4.2 and 4.8 m/s on average in control subjects, and was 3.6–4.3 m/s in patients with myositis. The CIM patient presented with markedly prolonged duration of the compound muscle action potential (CMAP). Normal MFCV in the CIM patient may suggest that the prolonged CMAP duration in CIM may not be due to the slowed MFCV, but to other mechanisms. MFCV measurement is a difficult technique, and its diagnostic role is yet to be documented, including for CIM.

Prolonged Compound Muscle Action Potential Duration and Its Pathological Correlation in Critical Illness Myopathy (P1.112)

Prolonged Compound Muscle Action Potential Duration and Its Pathological Correlation in Critical Illness Myopathy (P1.112)