Abductor Digiti Minimi Muscle Research Articles

Motor unit number estimation and quantitative needle electromyography in stroke patients

ObjectiveTo evaluate the effect of upper motor neuron damage upon motor units’ function by means of two separate and supplementary electrophysiological methods. MethodsThe abductor digiti minimi muscle of the non-paretic and the paretic side was studied in forty-six stroke patients with (a) motor unit number estimation (MUNE) – adapted multiple point stimulation method and (b) computerized quantitative needle electromyography (EMG) assessing the configuration of voluntary recruited motor unit potentials. Main outcome comparisons were focused on differences between non-paretic and paretic side. ResultsOn the affected hands mean MUNE value was significantly lower and mean area of the surface recorded single motor unit potentials was significantly larger than the corresponding ones on the non-paretic hands. EMG findings did not reveal remarkable differences between the two sides. Neither severity nor chronicity of stroke was related to MUNE or EMG parameters. DiscussionMUNE results, which suggested reduced motor unit numbers in stroke patients, in conjunction with the normal EMG features in these same muscles has given rise to different interpretations. In a clinical setting, reinnervation type changes in the EMG similar to that occurring in neuronopathies or axonal neuropathies should not be expected in muscles with central neurogenic lesion.

Ulnar nerve at the elbow – normative nerve conduction study

IntroductionA goal of our work was to perform nerve conduction studies (NCSs) of the ulnar nerve focused on the nerve conduction across the elbow on a sufficiently large cohort of healthy subjects in order to generate reliable reference data.MethodsWe examined the ulnar nerve in a position with the elbow flexion of 90o from horizontal. Motor response was recorded from the abductor digiti minimi muscle (ADM) and the first dorsal interosseous muscle (FDI).ResultsIn our sample of 227 healthy volunteers we have examined 380 upper arms with the following results: amplitude (Amp)-CMAP(wrist) for ADM 9.6 ± 2.3 mV, MNCV at the forearm 60.4 ± 5.2 m/s, MNCV across the elbow 57.1 ± 5.9 m/s.DiscussionOur study showed that motor NCSs of the ulnar nerve above elbow (AE) and below elbow (BE) in a sufficiently large cohort using methodology recommended by AANEM gave results well comparable for registration from FDI and ADM.

Possible implications of an accessory abductor digiti minimi muscle: a case report

BackgroundAccessory ADM was first reported in 1868 although muscular, vascular and nervous variations of the hypothenar eminence are rare, contrary to anomalous muscles in the wrist which are relatively common.Case presentationThis case report presents a bilateral variation of an accessory abductor digiti minimi muscle in a male specimen. Ulnar artery and ulnar nerves were taken into account regarding their position and trajectory related to this variation.ConclusionMuscle size may be an important factor in considering whether a variation is able to produce neurovascular compression and clinical implications.

Reference value of long-time exercise test in the diagnosis of primary periodic paralysis

The long-time exercise test (ET) is used to diagnose the primary periodic paralyses (PPs). However the reference values of ET are many and various. This study aimed to investigate the reference value of long-time ET in the diagnosis of PPs. We recruited 108 healthy subjects, 68 patients with PPs, and 72 patients with other diseases for the study. The procedure of ET was made on the basis of the McManis' method. Electrical responses were recorded from right abductor digiti minimi (ADM) muscle when stimulation of the ulnar nerve at the wrist. After the compound muscle action potential (CMAP) was monitored, subjects were then asked to contract the muscle as strongly as possible for 5 minutes. CMAPs were recorded for 2 seconds immediately after cessation of exercise, then every 5 minutes for 10 minutes, and finally every 10 minutes for 50 minutes. In general, the CMAP amplitudes will fall below the pre-exercise levels in an hour. The largest decrease was calculated and used as results of ET. The CMAP amplitude decreases had no significant differences between groups when the healthy adults were grouped according to age, gender, height, weight and test time. Decreases in PPs patients (57.76%) were significantly more than in healthy subjects (15.21%) and other disease patients (18.10%, P < 0.001). Receiver operating characteristic (ROC) curve analysis showed that the best threshold is 35.50%. In the long-time exercise test, threshold of 35.50% for the CMAP amplitude decrease was identified for abnormal. The result is not influenced by age, gender, height, weight, and test time. About 7.4% of healthy subjects were abnormal in ET.

C8 and T1 innervation of forearm muscles

ObjectiveC8-dominant innervation of ulnar-innervated and T1-dominant innervation of median-innervated intrinsic hand muscles have been suggested, although less is known regarding forearm muscles. We aimed to determine myotomal innervation of the forearm muscles based on the clinical and electromyographial findings of patients with C8 or T1 lesions. MethodsMedical Research Council scale and EMG findings were retrospectively reviewed in 16 patients with C8 lesions (2 postmedian sternotomy C8 plexopathy and 14 C8 radiculopathy) and 9 patients with T1-dominant lesions (8 true neurogenic thoracic outlet syndrome and 1 T1 radiculopathy). ResultsClinical and EMG findings revealed T1-dominant innervation of the flexor digitorum superficialis, flexor digitorum profundus of the index finger, abductor pollicis brevis, and flexor pollicis longus muscles, and C8-dominant innervation of the flexor carpi ulnaris, flexor digitorum profundus of the little finger, and digit extensors innervated by the posterior interosseous nerve. The first dorsal interosseous, and abductor digiti minimi muscles seem to be innervated by both C8 and T1 roots. ConclusionsC8-dominant innervation of ulnar-innervated muscles and T1-dominant innervation of median-innervated muscles are also evident for forearm flexor muscles. SignificanceSuch an additional evidence for myotomal innervation will improve localization in clinical as well as electrophysiological diagnoses.

Modulation of short-latency afferent inhibition depends on digit and task-relevance.

Short-latency afferent inhibition (SAI) occurs when a single transcranial magnetic stimulation (TMS) pulse delivered over the primary motor cortex is preceded by peripheral electrical nerve stimulation at a short inter-stimulus interval (∼20–28 ms). SAI has been extensively examined at rest, but few studies have examined how this circuit functions in the context of performing a motor task and if this circuit may contribute to surround inhibition. The present study investigated SAI in a muscle involved versus uninvolved in a motor task and specifically during three pre-movement phases; two movement preparation phases between a “warning” and “go” cue and one movement initiation phase between a “go” cue and EMG onset. SAI was tested in the first dorsal interosseous (FDI) and abductor digiti minimi (ADM) muscles in twelve individuals. In a second experiment, the origin of SAI modulation was investigated by measuring H-reflex amplitudes from FDI and ADM during the motor task. The data indicate that changes in SAI occurred predominantly in the movement initiation phase during which SAI modulation depended on the specific digit involved. Specifically, the greatest reduction in SAI occurred when FDI was involved in the task. In contrast, these effects were not present in ADM. Changes in SAI were primarily mediated via supraspinal mechanisms during movement preparation, while both supraspinal and spinal mechanisms contributed to SAI reduction during movement initiation.

Examination of hand muscle activation and motor unit indices derived from surface EMG in chronic stroke.

In this study, we used muscle and motor unit indices, derived from convenient surface electromyography (EMG) measurements, for examination of paretic muscle changes post stroke. For 12 stroke subjects, compound muscle action potential and voluntary surface EMG signals were recorded from paretic and contralateral first dorsal interosseous, abductor pollicis brevis, and abductor digiti minimi muscles. Muscle activation index (AI), motor unit number index (MUNIX), and motor unit size index (MUSIX) were then calculated for each muscle. There was a significant AI reduction for all the three muscles in paretic side compared with contralateral side, providing an evidence of muscle activation deficiency after stroke. The hand MUNIX (defined by summing the values from the three muscles) was significantly reduced in paretic side compared with contralateral side, whereas the hand MUSIX was not significantly different. Furthermore, diverse changes in MUNIX and MUSIX were observed from the three muscles. A major feature of the present examinations is the primary reliance on surface EMG, which offers practical benefits because it is noninvasive, induces minimal discomfort and can be performed quickly.

The effective neural drive to muscles is the common synaptic input to motor neurons.

Key points Despite the non‐linear property of individual motor neurons, the pool of motor neurons linearizes the relation between their common synaptic input and the neural drive to the muscle, i.e. the ensemble of axonal action potentials reaching the muscle from the spinal cord. In the frequency bandwidth relevant for force generation, the motor neuron pool attenuates the input signals sent independently to each motor neuron and transfers only the common signal components with a pure scaling. The effective neural drive to the muscle tends to exactly replicate, without phase distortion, the common synaptic input to motor neurons for increasing number of active motor neurons. The classic definition and functional meaning of motor unit synchronization are discussed in relation to the role of common input in determining the neural drive to muscle. AbstractWe analysed the transformation of synaptic input to the pool of motor neurons into the neural drive to the muscle. The aim was to explain the relations between common oscillatory signals sent to motor neurons and the effective component of the neural signal sent to muscles as output of the spinal cord circuitries. The approach is based on theoretical derivations, computer simulations, and experiments. It is shown theoretically that for frequencies smaller than the average discharge rates of the motor neurons, the pool of motor neurons determines a pure amplification of the frequency components common to all motor neurons, so that the common input is transmitted almost undistorted and the non‐common components are strongly attenuated. The effective neural drive to the muscle thus mirrors the common synaptic input to motor neurons. The simulations with three models of motor neuron confirmed the theoretical results by showing that the coherence function between common input components and the neural drive to the muscle tends to 1 when increasing the number of active motor neurons. This result, which was relatively insensitive to the type of model used, was also supported experimentally by observing that, in the low‐pass signal bandwidth, the peak in coherence between groups of motor units of the abductor digiti minimi muscle of five healthy subjects tended to 1 when increasing the number of motor units. These results have implications for our understanding of the neural control of muscles as well as for methods used for estimating the strength of common input to populations of motor neurons.

P544: Cortical hyperexcitability of the thenar group of intrinsic hand muscles may contribute to the split-hand sign in ALS

Objective Preferential wasting of the thenar group of intrinsic hand muscles including the abductor pollicis brevis (APB) and first dorsal interosseous (FDI) termed the split-hand sign, has been described as a specific feature of Amyotrophic Lateral Sclerosis (ALS). Greater corticomotorneuronal input to the thenar intrinsic hand muscles has been proposed as one of the pathophysiological mechanisms underlying the split hand sign and consequently difference in cortical excitability between the thenar and hypothenar intrinsic hand muscles was assessed in the present study, in a group of ALS patients and age matched healthy controls. Methods Cortical excitability was recorded using the threshold tracking transcranial magnetic stimulation (TMS) technique from the APB, FDI and abductor digiti minimi (ADM) muscles in 26 Awaji Criteria possible/probable ALS patients (17 male; 9 female; mean age 58.6 ± 1.9 years. Results were compared with 21 age matched healthy controls. Results Short interval intracortical inhibition (SICI) was globally reduced ( P P Conclusion There is a global increase in cortical excitability in ALS, further characterised by a preferential increase in cortical excitability of the APB and FDI muscles, which may underlie the clinical development of the ALS split-hand sign.

Electrophysiological evidence of functional improvement in the corticospinal tract after laminoplasty in patients with cervical compressive myelopathy: clinical article.

Cervical laminoplasty is a surgical procedure for cervical compressive myelopathy (CCM), and satisfactory outcomes have been reported. However, few reports have examined the pathophysiology of improvements in spinal cord function. The aim of this study was to investigate the variation in central motor conduction time (CMCT) before and after cervical laminoplasty in patients with CCM. Motor evoked potentials (MEPs) following transcranial magnetic stimulation and compound muscle action potentials (CMAPs) and F-waves following electrical stimulation of the ulnar and tibial nerves at the wrist and ankle were measured from the abductor digiti minimi muscle (ADM) and abductor hallucis muscle (AH) in 42 patients with CCM before and 1 year after cervical laminoplasty. The peripheral conduction time (PCT) was calculated as follows: (latency of CMAPs + latency of F-waves - 1)/2. The CMCT was calculated by subtracting the PCT from the onset latency of the MEPs. The CMCT recovery ratio was defined and calculated as the ratio of CMCT values 1 year after surgery to those before surgery. The CMCT data were analyzed as longer or shorter CMCT between the patients' right and left ADMs and AHs. The Japanese Orthopaedic Association (JOA) score for cervical myelopathy was obtained as a clinical outcome before and 1 year after surgery. The recovery rate (RR) 1 year after surgery was calculated using the following formula: (postoperative JOA score 1 year after surgery - preoperative JOA score)/(17 - preoperative JOA score) × 100. Correlations among CMCT parameters, patient age, JOA score, and RR were determined. The longer and shorter CMCTs from the ADM (longer, p = 0.000; shorter, p = 0.008) and the longer CMCT from the AH (longer, p = 0.000) before surgery decreased significantly 1 year after surgery; the shorter CMCT from the AH did not significantly differ (shorter, p = 0.078). The mean JOA score before surgery was 10.1 ± 3.0 and improved significantly to 12.9 ± 2.7 at 1 year after surgery (p = 0.000). The mean CMCT recovery ratio and RR were 0.91 ± 0.18 and 0.43 ± 0.27, respectively. The longer/shorter CMCT parameters in the ADM and AH before or 1 year after surgery correlated significantly with the JOA score both before and 1 year after surgery. The CMCT recovery ratio from the longer CMCT in the ADM correlated significantly with the RR (r = - 3090, p = 0.011). There were no significant correlations between age and any CMCT parameters or CMCT recovery ratios. These results suggest that cervical laminoplasty improves corticospinal tract function 1 year after surgery, which may be one of the reasons for the JOA score improvements in patients with CCM. The degree of improvement in corticospinal tract function did not correlate with patient age in this case series. The results demonstrated quantitative evidence of the pathophysiology of functional recovery in the corticospinal tract following cervical laminoplasty in patients with CCM.

Quantification of Myosignal Parameters in HD Patients

Developments in signal processing techniques, has made possible extraction of useful inside information from diseased myosignals through surface Electromyography (sEMG). This study attempts to quantify the myosignal parameter of Hansen's Disease (HD) patients. The EMG signals acquired from the Abductor Digiti Minimi (ADM) muscle were analyzed using time, frequency domain and wavelet techniques vis a vis healthy subjects. Quantifying the myosignals of the diseased-probably attempted for the first time-will help the physician in early diagnosis. Interestingly the test results show drastic deviation between the two. Its development and implementation will save the subjects from developing deformity.

52. Repetitive stimulation and Lambert–Eaton myasthenic syndrome

Lambert-Eaton myasthenic syndrome (LEMS) is a rare autoimmune disease with antibodies against voltage-controlled calcium channels (antiVGCC). The etiology can be paraneoplastic or idiopathic. Clinically, the patients have paresis of proximal muscle in the limbs, hyporeflexia, ptosis, fatigue, and autonomic symptoms. Electromyography is essential for diagnosis. The initial amplitude of the compound muscle action potential (CMAP) is strikingly low and is increased after facilitation. Low frequency repetitive nerve stimulation (LFS) 2–5 Hz shows decrement of amplitude and high frequency repetitive nerve stimulation (HFS) 20–50 Hz shows increment (increment over 100% is diagnostic for LEMS). The aim of the presentation is to share the electrophysiological findings in our three patients. Age of patients (females) were 30–57 years, the development of their disease was 0.2–4 years, all of them had positive antiVGCC type P/Q. One patient had a paraneoplastic form. If we stimulated abductor digiti minimi muscle (ADM), we found that the initial amplitude of CMAP was low in only one patient. LFS 3 Hz showed a decrement of at least 10% just in one patient and HFS 30 Hz showed increment 40%, 67% and 600% in these patients. If we stimulated abductor hallucis muscle (AH), the initial amplitude of CMAP was low only in one patient, LFS 3 Hz showed decrement of more than 10% in two patients and the HFS 30 Hz showed increment 117%, 136% and 200% in these patients. We consider that AH should be always investigated by HFS 30 Hz, where we constantly recorded increment over 100% in contrast to the stimulation of ADM.

Utility of dissociated intrinsic hand muscle atrophy in the diagnosis of amyotrophic lateral sclerosis.

The split hand phenomenon refers to predominant wasting of thenar muscles and is an early and specific feature of amyotrophic lateral sclerosis (ALS). A novel split hand index (SI) was developed to quantify the split hand phenomenon, and its diagnostic utility was assessed in ALS patients. The split hand index was derived by dividing the product of the compound muscle action potential (CMAP) amplitude recorded over the abductor pollicis brevis and first dorsal interosseous muscles by the CMAP amplitude recorded over the abductor digiti minimi muscle. In order to assess the diagnostic utility of the split hand index, ALS patients were prospectively assessed and their results were compared to neuromuscular disorder patients. The split hand index was significantly reduced in ALS when compared to neuromuscular disorder patients (P<0.0001). Limb-onset ALS patients exhibited the greatest reduction in the split hand index, and a value of 5.2 or less reliably differentiated ALS from other neuromuscular disorders. Consequently, the split hand index appears to be a novel diagnostic biomarker for ALS, perhaps facilitating an earlier diagnosis.

An examination of the influence of visuomotor associations on interpersonal motor resonance

The adaptation account of mirror neurons in humans proposes that mirror systems have been selected for in evolution to facilitate social cognition. By contrast, a recent “association” account of mirror neurons in humans argues that mirror systems are not the result of a specific adaptation, but of sensorimotor learning arising from concurrent visual and motor activity. Here, we used transcranial magnetic stimulation (TMS) and electromyography (EMG) to evaluate whether visuomotor associations affect interpersonal motor resonance, a putative measure of mirror system activity. 18 participants underwent two TMS sessions exploring whether visuomotor associations established throughout one׳s lifespan, namely common movements and movements generated from one׳s own perspective, are associated with increased putative mirror system activity. Our results showed no overall difference in interpersonal motor resonance to common versus uncommon actions, or actions presented from an egocentric (self) versus an allocentric (other) perspective. We did, however, observe increased interpersonal motor resonance within the abductor digiti minimi (ADM) muscle in response to allocentric compared to egocentric movements. As the association model predicts stronger mirror system response to actions with stronger visuomotor associations, such as common movements and those presented from an egocentric perspective, our findings provide little evidence to support the association model.

Abductor digiti minimi muscle flap in reconstruction of diabetic foot ulcers: A case series

Diabetic foot ulcers (DFUs), a leading cause of amputations, affect 15 % of people with diabetes. Wound coverage in these patients is changelling due to concurrent infection, neuropathy and vascular compromise. Though local muscle flaps were described by Ger et al. and popularized by Attinger et al., these small muscle flaps should be more routinary than they are now. A retrospective review of all patients with DFUs with exposed bone and osteomyelitis reconstructed by abductor digiti minimi muscle flaps and free skin grafting between January 2010 and December 2011 was conducted. This study included eight patients. Six patients had ulcers over the heel and two on the lateral aspect of the forefoot. All flaps survived well with no donor site complications. There was partial loss of skin graft in three cases and infection and total loss in one other case. Abductor digiti minimi is a safe and reliable flap that provides a durable cover. Level of evidence: Level IV, therapeutic study.

Cortical dysfunction underlies the development of the split-hand in amyotrophic lateral sclerosis.

The split-hand phenomenon, a specific feature of amyotrophic lateral sclerosis (ALS), refers to preferential wasting of abductor pollicis brevis (APB) and first dorsal interosseous (FDI) with relative preservation of abductor digiti minimi (ADM). The pathophysiological mechanisms underlying the split-hand phenomenon remain elusive and resolution of this issue would provide unique insights into ALS pathophysiology. Consequently, the present study dissected out the relative contribution of cortical and peripheral processes in development of the split-hand phenomenon in ALS. Cortical and axonal excitability studies were undertaken on 26 ALS patients, with motor responses recorded over the APB, FDI and ADM muscles. Results were compared to 21 controls. Short interval intracortical inhibition (SICI), a biomarker of cortical excitability, was significantly reduced across the range of intrinsic hand muscles (APBSICI ALS 0.3±2.0%, APBSICI controls 16.0±1.9%, P<0.0001; FDISICI ALS 2.7±1.7%, FDI SICI controls 14.8±1.9%, P<0.0001; ADMSICI ALS 2.6±1.5%, ADM SICI controls 9.7±2.2%, P<0.001), although the reduction was most prominent when recorded over APB/FDI. Changes in SICI were accompanied by a significant increase in motor evoked potential amplitude and reduction of cortical silent period duration, all indicative of cortical hyperexcitability, and these were most prominent from the APB/FDI. At a peripheral level, a significant increase in strength-duration time constant and reduction in depolarising threshold electrotonus were evident in ALS, although these changes did not follow a split-hand distribution. Cortical dysfunction contributed to development of the split-hand in ALS, thereby implying an importance of cortical hyperexcitability in ALS pathogenesis.

Guyon管症候群の神経伝導検査による検討

We conducted nerve conduction studies (NCSs) of the ulnar nerve in 10 patients with Guyon canal syndrome. In three patients, the distal latency (DL) of compound muscle action potentials (CMAPs) recorded from the first dorsal interosseous (FDI) muscles was significantly prolonged, whereas that recorded from the abductor digiti minimi (ADM) muscles was normal. These findings indicate deep motor branch (distal to hypothenar muscles) lesions. In one patient, abnormal CMAP findings were detected in the FDI and ADM muscles. These findings indicate deep motor branch (proximal to hypothenar muscles) lesions. In three patients, the results of sensory nerve conduction studies (SCS) performed on the little finger were abnormal, as were CMAP findings in the FDI and ADM muscles. These findings indicate lesions proximal to or within the Guyon canal. In three patients, the SCS results obtained from the little finger were abnormal, whereas those of the dorsal cutaneous branch of the ulnar nerve were normal. These findings indicate superficial terminal sensory branch lesions. Evaluation of CMAPs recorded from the FDI muscle and demonstration of a normal dorsal ulnar sensory response are necessary for site of lesion diagnosis in patients with Guyon canal syndrome.

Definition dependent properties of the cortical silent period in upper-extremity muscles, a methodological study

BackgroundTo explore if stimulus–response (S-R) characteristics of the silent period (SP) after transcranial magnetic stimulation (TMS) are affected by changing the SP definition and by changing data presentation in healthy individuals. This information would be clinically relevant to predict motor recovery in patients with stroke using stimulus–response curves.MethodsDifferent landmarks to define the SP onset and offset were used to construct S-R curves from the biceps brachii (BB) and abductor digiti minimi (ADM) muscles in 15 healthy participants using rectified versus non-rectified surface electromyography (EMG). A non-linear mixed model fit to a sigmoid Boltzmann function described the S-R characteristics. Differences between S-R characteristics were compared using paired sample t-tests. The Bonferroni correction was used to adjust for multiple testing.ResultsFor the BB, no differences in S-R characteristics were observed between different SP onset and offset markers, while there was no influence of data presentation either. For the ADM, no differences were observed between different SP onset markers, whereas both the SP offset marker “the first return of any EMG-activity” and presenting non-rectified data showed lower active motor thresholds and less steep slopes.ConclusionsThe use of different landmarks to define the SP offset as well as data presentation affect SP S-R characteristics of the ADM in healthy individuals.

Unusual Co-existence of Biaponeurotic Palmaris Longus and Accessory Abductor Digiti Minimi in man

The present study describes a rarely reported co-existence of variant muscles in the right upper limb of a male cadaver of 57 years of age, observed during routine anatomical dissection. There was a presence of the biaponeurotic palmaris longus with a central muscle belly in the anterior forearm region which was closely related to the median nerve. In addition to this, an accessory abductor digiti minimi muscle was also reported in the corresponding hypothenar region, traversing the Guyon's canal, passing superficial to the ulnar vessels and nerves. Biaponeurotic palmaris longus and accessory abductor digiti minimi are important structural causes of the entrapment neuropathies of forearm and wrist. Diagnosis of these muscles as a cause of entrapment neuropathies requires the sound knowledge of variant muscles in the forearm and wrist region.

Interaction between the premotor processes of eye and hand movements: Possible mechanism underlying eye–hand coordination

Interaction between the execution process of eye movement and that of hand movement must be indispensable for eye–hand coordination. The present study investigated corticospinal excitability in the hand muscles during the premotor processes of eye and/or hand movement to elucidate interaction between these processes. Healthy humans performed a precued reaction task of eye and/or finger movement and motor-evoked potentials in the hand muscles were evoked in the reaction time. Leftward eye movement suppressed corticospinal excitability in the right abductor digiti minimi muscle only when little finger abduction was simultaneously executed. Corticospinal excitability in the first dorsal interosseous muscle was not suppressed by eye movement regardless of whether or not it was accompanied by finger movement. Suppression of corticospinal excitability in the hand muscles induced by eye movement in the premotor period depends on the direction of eye movement, the muscle tested, and the premotor process of the tested muscle. The suppression may reflect interaction between the motor process of eye movement and that of hand movement particularly active during eye–hand coordination tasks during which both processes proceed.