Central Conduction Time Research Articles

Age- and sex-related differences in brainstem auditory evoked potentials in secondary school students living in Northern European Russia

Brainstem auditory evoked potentials (BAEPs) were studied in 46 1st- to 11th-year students (22 boys and 24 girls) of a rural secondary school in Arkhangel’sk oblast. The objective of this work was to study age- and sex-related differences in BAEP characteristics in children and adolescents, living in the North and assess the BAEP characteristics as compared to reference values. In all three age groups of students, interpeak intervals I–III, III–V, and I–V characterizing the peripheral and central conduction times were shorter in girls than in boys. Interpeak interval III–V tended to increase with age only in boys (at puberty), with a significant increase in the latencies of waves I, III, and V. The BAEP characteristics in the subjects examined included a shorter peak latency and a greater amplitude of wave I (except senior students), relatively prolonged interpeak interval I–III, and more pronounced sex-related differences in BAEPs, especially at puberty. These findings show that it is necessary to revise regional reference values for BAEPs, differentiated by sex and age, including at puberty.

Brain volume analyses and somatosensory evoked potentials in multiple system atrophy

We investigated a progression of brain atrophy and somatosensory system dysfunction in multiple system atrophy (MSA). Subjects were 21 MSA patients [12 MSA-C (cerebellar type) and 9 MSA-P (parkinsonism type)]. The relative volumes of cerebrum, brainstem and cerebellum to the intracranial volume were obtained from three-dimensional computed tomography (3D-CT) of the brain. The median nerve somatosensory evoked potentials (SEPs) were recorded, and the latencies and amplitudes of N9, N11, P13/14, N20 and P25 components were measured. We studied correlations between brain volumes, SEP and clinical features. The brainstem and cerebellar atrophies were aggravated with progression of the disease. The central sensory conduction time (CSCT) was progressively prolonged in parallel with the disease duration irrespective of the actual age of the patients. In MSA patients, the volume reductions of cerebellum and brainstem could be one of structural markers of disease progression, and the sensory pathway is progressively involved with the progression of disease processes.

Multimodality-evoked potential study of anti-aquaporin-4 antibody-positive and -negative multiple sclerosis patients

Neuromyelitis optica (NMO) is claimed to be a distinct disease entity from multiple sclerosis (MS) because of its strong association with NMO-IgG/anti-AQP4 antibody; however, the in vivo role of the antibody remains unknown. Therefore, we aimed to clarify whether the presence of anti-AQP4 antibody is associated with any abnormalities in multimodality-evoked potentials in 111 patients with relapsing–remitting or relapsing-progressive MS, including the opticospinal form of MS, 18 of whom were seropositive for anti-AQP4 antibody. More patients with anti-AQP4 antibody showed a lack of the P100 component on visual-evoked potentials (VEPs) than those without the antibody (11/17, 64.7% vs. 20/84, 23.8%, p = 0.003), whereas the frequency of delayed P100 latency was significantly higher in the latter group than in the former (1/17, 5.9% vs. 28/84, 33.3%, p = 0.021). The frequencies of non-responses and delayed central sensory conduction times in median and posterior tibial nerve somatosensory-evoked potentials (SEPs) were not significantly different between anti-AQP4 antibody-positive and -negative patients. In terms of upper and lower limb motor-evoked potentials (MEPs), the frequencies of non-responses and delayed central motor conduction times did not differ significantly based on the presence or absence of anti-AQP4 antibody. The frequency of optic nerve lesions on MRI was significantly higher in anti-AQP4 antibody-positive patients than in anti-AQP4 antibody-negative patients ( p = 0.0137). Multiple logistic analyses revealed that anti-AQP4 antibody positivity (OR = 8.406, p = 0.02) and unevoked VEP responses (OR = 35.432, p < 0.001) were significantly related to development of severe visual impairment. Such an association of anti-AQP4 antibody with disability was not found for either severe motor or sensory impairment. These findings suggest a distinctive nature of optic nerve lesions between anti-AQP4 antibody-positive and -negative patients; lesions are supposed to be more necrotic in the former group and more demyelinating in the latter.

White matter lucencies in multi-infarct dementia: a somatosensory evoked potentials and CT study

White matter low attenuation (WMLA) on computed tomography (CT) and the central conduction time (CCT) measured by median nerve-somatosensory evoked potentials were examined in 12 multi-infarct dementia (MID) patients, 10 patients with multiple infarcts (MI) without dementia and 11 age-matched controls. Patients with deep vascular lesions without cortical infarcts on CT were included. In MID, prolongation of CCT and moderate to severe WMLA were observed. The CCT and WMLA in MI patients were intermediate. The CCT was longer when the WMLA was more extensive. The result suggests that white matter disease in MID is concerned to the occurrence of dementia by disturbing axonal conduction.

Short latency somatosensory evoked potentials in Charcot-Marie-Tooth disease. A family with an intermediate form.

9 patients with Charcot-Marie-Tooth Disease (CMTD) of intermediate type (PMA type II, 10), all from the same family, presented with a significant increase of the interpeak N9-N13 latency. This increase is already present in the pre-symptomatic phase of the disease and there is no significant difference between the various patients of different ages and clinical severity, indicating that the lesions appears very early and tends to establish itself equally early. Similar behaviour is also seen in the distal conduction velocity along the sensitive fibres, while the more proximal areas seem to be relatively spared. The authors interpret these data as an expression of a distal central peripheral sensory neuropathy. In contrast, the lesion of the peripheral motor fibres, particularly in the legs, has a different and more severe pattern of evolution. Alterations in central conduction time (N13-N20) were not seen in any of the 9 patients studied.

Subclinical lithium neurotoxicity: correlation of neural conduction abnormalities and serum lithium level in manic-depressive patients with lithium treatment

Nerve conduction velocities (NCVs) and multimodality evoked potentials were studies in 28 manic-depressive patients under lithium prophylaxis with serum lithium levels between 0.320 and 0.980 mEq/L. Slowing of motor and sensory NCVs and prolonged central neural conduction times obtained from somatosensory and brainstem auditory evoked potentials were found to correlate with serum lithium levels. Lithium-induced changes in cell membrane conductivity and in the synaptic transmission are considered responsible for the neurotoxic effects of lithium.

Memory and psychomotor impairment following high-dose interferon treatment in amyotrophic lateral sclerosis.

Patients with amyotrophic lateral sclerosis were treated with high-dose intravenous infusion of human leukocyte interferon for six days. Neuropsychological examinations were carried out before, during and after the treatment. Marked reversible dysfunction was detected in immediate memory functions, coordination of hand movements, and drawing. Motor perseveration, micrographia, and slowing of behaviour were also observed. Changes appeared four to 12 days after start of treatment, with the peak on days six to eight. Recovery was almost complete by day 15. Intellectual ability, as measured by three WAIS subtests, praxis of hand movements, visuognostic functions, speech, reading, writing, and calculation remained essentially unaffected. The profile of the neuropsychological deficits observed, the absence of defects typical of focal posterior cortical lesions, the simultaneously slowed electroencephalographic activity with frontal accentuation, and the increased central conduction times of brain stem auditory evoked potentials suggest frontobasal involvement.

Neurological complications of ankylosing spondylitis: neurophysiological assessment

Studies examined the neurological involvement of ankylosing spondylitis (AS) are limited. This study aimed to assess the frequency of myelopathy, radiculopathy and myopathy in AS correlating them to the clinical, radiological and laboratory parameters. Included were 24 patients with AS. Axial status was assessed using bath ankylosing spondylitis metrology index (BASMI). Patients underwent (a) standard cervical and lumbar spine and sacroiliac joint radiography, (b) somatosensory (SSEP) and magnetic motor (MEP) evoked potentials of upper and lower limbs, (c) electromyography (EMG) of trapezius and supraspinatus muscles. Patients' mean age and duration of illness were 36 and 5.99 years. Bath ankylosing spondylitis metrology index mean score was 4.6. Twenty-five percent (n = 6) of patients had neurological manifestations, 8.3% of them had myelopathy and 16.7% had radiculopathy. Ossification of the posterior (OPLL) and anterior (OALL) longitudinal ligaments were found in 8.3% (n = 2) and 4.2% (n = 1). About 70.8% (n = 17) had >or=1 neurophysiological test abnormalities. Twelve patients (50%) had SSEP abnormalities, seven had prolonged central conduction time (CCT) of median and/or ulnar nerves suggesting cervical myelopathy. Six had delayed peripheral or root latencies at Erb's or interpeak latency (Erb's-C5) suggesting radiculopathy. Motor evoked potentials was abnormal in 54% (n = 13). Twelve (50%) and five (20.8%) patients had abnormal MEP of upper limbs and lower limbs, respectively. About 50% (n = 12) had myopathic features of trapezius and supraspinatus muscles. Only 8.3% (n = 2) had neuropathic features. We concluded that subclinical neurological complications are frequent in AS compared to clinically manifest complications. Somatosensory evoked potential and MEP are useful to identify AS patients prone to develop neurological complications.

The Utility of Median Somatosensory Evoked Potentials in Anoxic-Ischemic Coma

The early recognition of comatose patients with a hopeless prognosis--regardless of how aggressively they are managed--is of utmost importance. Median somatosensory evoked potentials (SSEP) supplement and enhance neurological examination findings in anoxic-ischemic coma and are useful as an early guide in predicting outcome. The key finding is that bilateral absence of cortical evoked potentials reliably predicts unfavorable outcome in comatose patients after cardiac arrest. The author studied 50 comatose patients with preserved brainstem function after cardiac arrest. All 23 patients with bilateral absence of cortical evoked potentials died without awakening. Neuropathological study in seven patients disclosed widespread ischemic changes or frank cortical laminar necrosis. The remaining 27 patients with normal or delayed central conduction times had an uncertain prognosis because some died without awakening or entered a persistent vegetative state. The majority of patients with normal central conduction times had a good outcome, whereas a delay in central conduction times increased the likelihood of neurological deficit or death. Greater use of SSEP in anoxic-ischemic coma would identify those patients unlikely to recover and would avoid costly medical care that is to no avail.

Two Patients with Congenital Insensitivity to Pain with Anhidrosis Showing Marked Prolongation of Central Conduction Time in Short Latency Somatosensory Evoked Potential

Two Patients with Congenital Insensitivity to Pain with Anhidrosis Showing Marked Prolongation of Central Conduction Time in Short Latency Somatosensory Evoked Potential

The role of axonopathy in the mechanisms of development of demyelination processes in the central and peripheral nervous system

The role of axonopathy in the development of demyelinating processes in the CNS and peripheral nervous system was addressed in studies of 43 patients with multiple sclerosis (MS) and 144 patients with chronic inflammatory demyelinating polyneuropathy (CIDPN). Patients with MS were found to have foci of reduced MRI intensity in the T1 regime ("black holes," present in 28%) and regional atrophy of the cerebral cortex (in 46%), which showed a significant association with the degree of invalidity on the EDSS (Kendall tau = 0.38 and 0.43; p = 0.038 and 0.021, respectively). The mean fatigue score on the FSS was 4.9 (3.6; 5.4). A significant increase in the central conduction time on the background of fatigue (p = 0.016), along with an absence of signs of impaired reliability of neuromuscular transmission and an absence of past-activation phenomena, suggested that central mechanisms were predominant in the formation of fatigue phenomena in MS. In addition, 34.9% of patients with MS showed signs of peripheral nervous system involvement, while the clinical-electrophysiological pattern in 12.5% of patients with CIDPN showed signs of CNS involvement. These data widen existing concepts of the mechanisms of formation of axonopathy in the CNS, based on evidence for the development of axon-demyelinating processes in CIDPN, which is the most accessible model of demyelination for study using contemporary neurophysiological methods.

Somatosensory Evoked Potentials by Median Nerve Stimulation in Children During Thiopental/Sevoflurane Anesthesia and the Additive Effects of Ketoprofen and Fentanyl

Somatosensory evoked potentials (SEPs) are used to determine the spinal cord and brain function during surgical procedures. In general, SEPs are sensitive to volatile anesthetics, but little is known about the effects of anesthesia maintenance with sevoflurane on SEPs in children. Analgesics are often provided during anesthesia, and supplementary drugs may also affect the SEPs. In this prospective clinical trial of 27 healthy, 3- to 8-yr-old children, we evaluated the effects of sevoflurane anesthesia after IV induction with benzodiazepine and barbiturate on median nerve SEP. In addition, the effects of two analgesics (ketoprofen and fentanyl) on SEPs were evaluated. Median nerve SEPs were recorded before premedication with midazolam 0.1 mg/kg IV, and at three separate times during anesthesia maintenance with sevoflurane 2% end-tidal concentration in air/oxygen (after 15 min of sevoflurane inhalation), supplemented with/without ketoprofen 1 mg/kg (after 25 min) and fentanyl 1 microg/kg (after 35 min). Compared with baseline measurements, an increase both in N20 latency (P = 0.015) and in central conduction time (P = 0.001) was noted during anesthesia maintenance with sevoflurane. The administration of analgesics did not have an influence on the N20 latency or central conduction time. In children 5 to 8 yr of age, the mean cortical N20-P25 amplitude was decreased (P = 0.008). In addition, in older children, the N20-P25 amplitude decreased after the co-administration of ketoprofen and fentanyl compared with the values measured before the analgesics (P = 0.03). These decreases were not seen in the younger children. In children, anesthesia maintenance with 2% sevoflurane prolongs median SEP latencies in a manner that is similar to those reported for other volatile anesthetics. However, SEP monitoring can be done with sevoflurane inhalation, but the dosage should be adjusted due to interindividual variability. Co-administration of ketoprofen, and fentanyl did not affect the SEP latencies, but post hoc analysis suggested that older children had a decrease in cortical amplitudes.

Subcortical somatosensory evoked potentials after posterior tibial nerve stimulation in children

We report our normative data of somatosensory evoked potentials (SEP) after posterior tibial nerve (PTN) stimulation from a group of 89 children and 18 adults, 0.4–29.2 years of age. We recorded near-field potentials from the peripheral nerve, the cauda equina, the lumbar spinal cord and the somatosensory cortex. Far-field potentials were recorded from the scalp electrodes with a reference at the ipsilateral ear. N8 (peripheral nerve) and P40 (cortex) were present in all children but one. N20 (cauda equina) and N22 (lumbar spinal cord) were recorded in 94 and 106 subjects, respectively. P30 and N33 (both waveforms probably generated in the brainstem) were recorded in 103 and 101 subjects, respectively. Latencies increased with age, while central conduction times including the cortical component, decreased with age (up to about age 10 years). The amplitudes of all components were very variable in each age group. We report our normative data of the interpeak latencies N8–N22 (peripheral conduction time), N22–P30 (spinal conduction time), N22–P40 (central conduction time) and P30–P40 (intracranial conduction time). These interpeak latencies should be useful to assess particular parts of the pathway. The subcortical PTN-SEPs might be of particular interest in young or retarded children and during intraoperative monitoring, when the cortical peaks are influenced by sedation and sleep, or by anesthesia.

Subcortical somatosensory evoked potentials after median nerve and posterior tibial nerve stimulation in high cervical cord compression of achondroplasia

Children with achondroplasia may have high cervical myelopathy from stenosis of the cranio-cervical junction resulting in neurological disability and an increased rate of sudden death. To detect myelopathy we recorded somatosensory evoked potentials after median nerve (MN) and posterior tibial nerve (PTN) stimulation in 77 patients with achondroplasia aged 0.3–17.8 years (mean 2.7 years). In addition to the conventional technique of recording the cortical components and the central conduction time (CCT) we employed non-cephalic and mastoid reference electrodes to record the subcortical waveforms N13b and P13 (MN-SEP) as well as P30 (PTN-SEP), respectively, which are generated near the cranio-cervical junction. The findings were related to the MRI results. Thirty-four patients had abnormal MRI findings including spinal cord compression ( n = 28) and/or myelomalacia ( n = 24) at or below the cranio-cervical junction. The sensitivity of the MN-SEPs was 0.74 including all abnormal upper cervical cord MRI findings (specificity 0.98), and the sensitivity was 0.79 (specificity 0.92) for cervical cord compression, respectively. The sensitivity of the PTN-SEPs was 0.52 (specificity 0.93) for all abnormal MRI findings and 0.59 (specificity 0.92) for cervical cord compression. The subcortical SEPs N13b and P13 as well as P30 were more sensitive than the conventional recordings. The MN-SEPs, notably the subcortical tracings, are useful for the detection of cervical myelopathy in children with achondroplasia. The PTN-SEPs are less sensitive. However, the tibial nerve SEPs might contribute additional information from the lumbar or thoracic spinal cord, which was, however, not tested in this study.

Intra-cortical connectivity in multiple sclerosis: a neurophysiological approach

Multiple sclerosis is an autoimmune disease predominantly affecting the white matter of the CNS, causing--among functional sequelae-cortico--cortical partial or total disconnection. Since functional connectivity linking cerebral regions is reliably reflected by synchronization of their neuronal firing, in this study an electrophysiological parameter measured by magnetoencephalography was used to quantify an intra-cortical connectivity (ICC) index focused on the primary somatosensory cortical areas (S1). Twenty-one patients affected by mild (Extended Disability Scale Score, median 1,5) relapsing-remitting (RR) multiple sclerosis in the remitting phase without clinically evident sensory impairment were evaluated. Three dimensional MRI was used to quantify the lesion load, discriminating black hole and non-black hole portions, normalized by individual brain volumes. When matched with a control population, multiple sclerosis patients showed a reduced ICC combined with the complete loss of the finger-dependent functional specialization in S1 cortex of the dominant hemisphere. No association was found between ICC impairment and disease duration, or prolongation of the central sensory conduction time, presence of spinal cord lesions and ongoing disease modifying therapy. The ICC index slightly correlated with the lesion load. A local index of ICC in a circumscribed brain primary area was altered in mildly disabled RR-multiple sclerosis patients, also in absence of any impairment of central sensory conduction. In conclusion, the diffuse damage influencing the multi-nodal network subtending complex cerebral functions also affects intrinsic cortical connectivity. The S1 ICC index is proposed as a highly sensitive and simple-to-test functional measure for the evaluation of intra-cortical synchronization mechanisms in RR-multiple sclerosis.

TUO07 Somatosensory processing in very prematurely born infants recorded with magnetoencephalography

Methods: An electrophysiological parameter measured by Magnetoencephalography was used to quantify an Intra-Cortical Connectivity (ICC) index focused on the primary somatosensory cortical areas (S1). Twenty one patients affected by mild (Extended Disability Scale Score, EDSS, mean 1,7 range 0-3,5) relapsing-remitting multiple sclerosis (RR-MS) in the remitting phase without clinically evident sensory impairment were evaluated. Three dimensional magnetic resonance imaging (3D-MRI) was used to quantify the lesion load, discriminating black hole (BH) and non-BH portions, normalized by individual brain volumes. Results: When matched with a control population, MS patients showed a reduced ICC, combined with the complete loss of the finger-dependent functional specialization in left S1 cortex. No association was found between ICC impairment and disease duration, or prolongation of the central sensory conduction time, evidence of spinal cord lesions and disease modifying therapy. The ICC index slightly correlated with the lesion load. Conclusion:A local index of intra-cortical connectivity in a circumscribed brain primary area was altered in mildly disabled RR-MS patients, also in absence of any impairment of central sensory conduction. It is concluded that the diffuse damage influencing the multi-nodal network subtending complex cerebral functions also affects intrinsic cortical connectivity. S1 ICC is proposed as a highly sensitive and simple-to-test functional index for the evaluation of the widespread cerebral damage in RR-MS.

The role of somatosensory evoked potentials in detecting cerebral ischaemia during carotid endarterectomy

The generation of shunt criteria by somatosensory evoked potentials is controversial. This study was designed to validate somatosensory evoked potentials' tracings and their derived shunt criteria compared with clinical-neurological examination. We prospectively studied the somatosensory evoked potentials' tracing in 102 patients who underwent carotid endarterectomy under cervical plexus blockade, comparing different somatosensory evoked potentials' derived thresholds of impaired cerebral blood flow with the neurological examination. The 50% reduction of the primary cortical response to median nerve stimulation as threshold of critical cerebral blood flow showed a sensitivity of 87% and a specificity of 66%. In case of total collapse of primary cortical response, we observed a sensitivity of 85% and a specificity of 89%. Concerning the prolongation of central conduction time between the spinal response at N13 and the cortical response at N20/P25 as critical threshold of impaired cerebral blood flow, the sensitivity was 87% and specificity 40%. The need-to-shunt index with its threshold at >0.5 showed a sensitivity of 85% and a specificity of 88%. Compared to other studies, we have shown a much lower sensitivity and specificity of somatosensory evoked potentials in detecting critical cerebral perfusion; thus its use remains controversial and has to be assessed in further investigations.

Reorganization of the cortico-spinal pathway in patients with chronic complete thoracic spinal cord injury: A study of motor evoked potentials

To evaluate the change in motor evoked potential parameters following transcranial magnetic stimulation in patients with chronic complete thoracic cord injury. A cross-sectional study. Eighteen patients with chronic complete thoracic cord injury and 18 age- and sex-matched healthy controls were included in the study. The mean post-injury duration was 13.0 (standard deviation (SD) 6.0) years. The latency, amplitude, central conduction time and peripheral conduction time of motor evoked potentials from bilateral abductor pollicis brevis and first dorsal interosseous muscles following transcranial magnetic stimulation were measured and compared between the patients and healthy controls. The predicting variables for central conduction time, including age, sex, height, illness duration and job activity, were analysed using a simple correlation and stepwise multiple regression model. The patients with complete thoracic cord injury had longer central conduction time recording of the dominant hand in both abductor pollicis brevis and first dorsal interosseous muscles. The difference in latency approached significance between the patients and controls. There was no statistical difference in amplitude between them. Regression analysis demonstrated that patients who were older, less physically active and with longer illness duration showed prolonged central conduction time. The central conduction time in the dominant hand of chronic complete thoracic cord injury is prolonged. This study revealed motor reorganization of the central nervous system in complete thoracic cord injury. Decreased physical activity and prolonged illness may cause these changes.

Effect of early onset otitis media on brainstem and cortical auditory processing

BackgroundOtitis media (OM) leads to significant reduction in the hearing sensitivity. The reduced auditory input, if in the early years of life when the auditory neural system is still maturing, may adversely influence the structural as well as functional development of the system. Past research has reported abnormalities in both the structure and function of brainstem nuclei following auditory deprivation, but, it has not necessarily focused on children who had OM in their first year of life. It can also be said that if auditory processing is affected at the brainstem level because of early onset OM (reduced auditory input in the crucial periods of neural development), then, it may be said that auditory processing is also affected at the cortical level because it receives distorted input from the brainstem. Therefore, the purpose of this study was to document the effects of early onset OM on auditory processing, if any, at the brainstem as well as at cortical levels. A related purpose of the study was to investigate the persistence of the effects of early onset OM, if any, on auditory processing.MethodsA cross sectional approach and a standard group comparison design was used in the study. Thirty children, who had OM between 6 and 12 months of age and who were in the age range of 3.1 – 5.6 years participated in the study. Children with OM were divided into 3 groups based on their age. Click evoked auditory brainstem responses (ABRs) and late latency responses (LLRs) were recorded from these children, and the responses were compared with those from age and gender matched normal children without any history of OM. The data from the 2 groups was statistically analyzed through independent t test. Pearson's Product Moment correlation was computed to examine the relationship between results of ABR and LLR in children with early onset OM.ResultsThe mean central conduction time was significantly increased and the mean amplitude of wave I and III of ABRs was significantly reduced in children with early onset OM compared to normal children. Also, the latency of all LLR waves was significantly less in children with early onset OM than in normal children. However, significant differences in mean values of either ABR or LLR (latencies or interwave intervals as the case may be) were observed only in 3-year old children. There was a significant, but negative association between central conduction time and latency of LLRs.ConclusionOM in the first year of life leads to negative effects on brainstem signal processing even if it has occurred only for a short duration (maximum of 3 months). In such a situation, auditory cortical structures probably show compensatory changes through central gain to offset the prolonged central conduction time. Although the results of the present study showed that the negative effects of early onset OM (occurring in the first year of life) on auditory processing disappeared by the time the children were 4.1 years, there is need for longitudinal studies on this to confirm the findings.

Cortical excitability in Duchenne muscular dystrophy

Objective To investigate the probable cortical excitability changes in DMD by electrophysiological means. Methods Sixteen cases with DMD, 10 age-matched control children (CC) and 10 healthy adult volunteers (AC) were studied with a transcranial magnetic stimulation (TMS) test battery composed of central conduction time, cortical silent period and paired TMS paradigm. Results There were no significant differences between DMD and CC groups except for lower amplitude motor responses in DMD cases. These two groups showed a similar pattern of excitability with less short interval intracortical inhibitions and shorter silent period durations as compared to the AC subjects. Conclusions The electrophysiological tests performed in our DMD patients did not reveal abnormalities caused particularly by the disorder. Significance TMS excitability studies performed in DMD boys may not provide findings other than those related to the developmental age.