Journal of Clinical Neuroscience 20 (2013) 383–388

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Journal of Clinical Neuroscience

journal homepage: www.elsevier .com/ locate/ jocn

Clinical Study

Brainstem auditory evoked potentials and middle latency auditory evokedpotentials in young children

Jin Jun Luo a,b,⇑, Divya S. Khurana c, Sanjeev V. Kothare c,1

a Department of Neurology, Temple University School of Medicine, Philadelphia, PA 19140, USAb Department of Pharmacology, Temple University School of Medicine, Philadelphia, USAc Section of Neurology, Department of Pediatrics, St. Christopher’s Hospital for Children, Drexel University College of Medicine, Philadelphia, USA

a r t i c l e i n f o a b s t r a c t

Article history:Received 1 December 2011Accepted 26 February 2012

Keywords:Auditory evoked potentialsBAEPMLAEP

0967-5868/$ - see front matter � 2012 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.jocn.2012.02.038

⇑ Corresponding author at: J.J. Luo, 3401 N. BroadNeurology, Temple University School of Medicine, Ph

E-mail address: jluo@temple.edu (J.J. Luo).1 Present address: Division of Epilepsy and Clinical

of Neurology, Children’s Hospital, Harvard Medical Sch

Measurements of brainstem auditory evoked potentials (BAEP) and middle latency auditory evokedpotentials (MLAEP) are readily available neurophysiologic assessments. The generators for BAEP arebelieved to involve the structures of cochlear nerve, cochlear nucleus, superior olive complex, dorsaland rostral pons, and lateral lemniscus. The generators for MLAEP are assumed to be located in the sub-cortical area and auditory cortex. BAEP are commonly used in evaluating children with autistic and hear-ing disorders. However, measurement of MLAEP is rarely performed in young children. To explore thefeasibility of this procedure in young children, we retrospectively reviewed our neurophysiology data-bank and charts for a 3-year period to identify subjects who had both BAEP and MLAEP performed. Sub-jects with known or identifiable central nervous system abnormalities from the history, neurologicexamination and neuroimaging studies were excluded. This cohort of 93 children up to 3 years of agewas divided into 10 groups based on the age at testing (upper limits of: 1 week; 1, 2, 4, 6, 8, 10 and12 months; 2 years; and 3 years of age). Evolution of peak latency, interpeak latency and amplitude ofwaveforms in BAEP and MLAEP were demonstrated. We concluded that measurement of BAEP andMLAEP is feasible in children, as early as the first few months of life. The combination of both MLAEPand BAEP may increase the diagnostic sensitivity of neurophysiologic assessment of the integrity or func-tional status of both the peripheral (acoustic nerve) and the central (brainstem, subcortical and cortical)auditory conduction systems in young children with developmental speech and language disorders.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Brainstem auditory evoked potentials (BAEP) are the electricalresponses recorded in the relevant auditory pathways provokedby auditory stimulation. BAEP are usually recorded for up to10 ms, triggered by click-stimulation. The generators for waves I,II, III, IV and V of BAEP are believed to involve the structures of co-chlear nerve, cochlear nucleus, superior olive complex, dorsal androstral pons, and lateral lemniscus, respectively.1 Waves II and IVvary significantly and may vary from person to person while wavesI, III and V are stable with high reproducibility, reliability and inter-individual consistency. BAEP are sensitive to brainstem lesionsfrom tumors, trauma, hemorrhage, ischemia, demyelination andmetabolic insult.2,3 The unique properties of BAEP enable reliable

ll rights reserved.

Street, C525, Department ofiladelphia, PA 19140, USA.

Neurophysiology, Departmentool, Boston, MA 02115, USA.

interpretation independent of the level of consciousness, sedativemedications and general anesthesia. BAEP are a useful intraopera-tive monitoring tool during brainstem, acoustic nerve or posteriorfossa tumor surgery,4–6 and for the prognostication of coma orstroke.7–10 Studies of BAEP are helpful in evaluating the functionalstatus of the peripheral and central auditory pathways. Abnormal-ities or disappearance of the individual waveforms, and delay inthe peak latencies (PL) and/or the interpeak latencies (IPL) indicateabnormalities involving either the relevant fibers and/or the gener-ator(s) in the auditory conduction pathways.1 Therefore, BAEP area useful tool in the evaluation of children with suspected hearingdisorders involving the cochlea, acoustic nerve and brainstem.11

MLAEP are usually recorded for up to 100 ms in adults after theclick-stimulation. The generators for the waveforms denoted as P0and Na are assumed to be in the subcortical regions while those forPa, Nb and Pb are thought to arise in the auditory cortex, or Hes-chl’s gyrus, of normal subjects.12–17 Measurement of the IPL ofP0–Pa and/or Na–Pa waveforms of the MLAEP is the most relevantparameter in the assessment of the auditory pathway between theupper brainstem and auditory cortex. A combination of BAEP andMLAEP measurement may thus aid in the investigation of the

Table 1Measures of peak latency, interpeak latency and amplitude in brainstem auditory evoked potentials

Upper limit of age group n I PL III PL V PL I–III IPL III–V IPL I–V IPL I Amp V Amp Ratio V/I amp

1 week 7 3.37 ± 0.27 4.70 ± 0.57 7.01 ± 0.59 3.01 ± 0.55 2.32 ± 0.11 5.33 ± 0.58 0.42 ± 0.17 0.37 ± 0.23 0.92 ± 0.381 month 8 3.69 ± 0.76 4.91 ± 0.21 7.22 ± 0.43 3.10 ± 0.31 2.41 ± 0.20 5.38 ± 0.47 0.40 ± 0.13 0.23 ± 0.10 0.62 ± 0.282 months 13 3.42 ± 0.43 4.67 ± 0.29 6.85 ± 0.47 2.99 ± 0.23 2.13 ± 0.19 5.14 ± 0.34 0.45 ± 0.16 0.33 ± 0.11 0.79 ± 0.304 months 7 3.61 ± 0.57 4.50 ± 0.31 6.60 ± 0.38 2.69 ± 0.33 2.10 ± 0.12 4.79 ± 0.41 0.60 ± 0.20 0.39 ± 0.08 0.74 ± 0.236 months 9 3.45 ± 0.58 4.39 ± 0.29 6.35 ± 0.33 2.67 ± 0.21 2.01 ± 0.12 4.62 ± 0.30 0.54 ± 0.36 0.43 ± 0.16 0.97 ± 0.478 months 4 3.56 ± 0.57 4.36 ± 0.24 6.29 ± 0.25 2.58 ± 0.11 1.93 ± 0.11 4.51 ± 0.05 0.58 ± 0.24 0.37 ± 0.21 0.63 ± 0.2610 months 3 3.33 ± 0.29 4.13 ± 0.19 6.09 ± 0.34 2.46 ± 0.05 1.97 ± 0.19 4.43 ± 0.21 0.52 ± 0.26 0.52 ± 0.20 1.31 ± 0.8312 months 5 3.30 ± 0.18 4.10 ± 0.15 6.17 ± 0.21 2.44 ± 0.10 2.07 ± 0.14 4.52 ± 0.21 0.69 ± 0.32 0.50 ± 0.06 0.86 ± 0.412 years 23 3.23 ± 0.31 4.10 ± 0.39 6.21 ± 0.73 2.49 ± 0.34 2.11 ± 0.4 4.59 ± 0.71 0.61 ± 0.20 0.51 ± 0.19 0.91 ± 0.403 years 14 3.19 ± 0.27 3.96 ± 0.25 5.86 ± 0.27 2.36 ± 0.21 1.91 ± 0.11 4.27 ± 0.21 0.71 ± 0.14 0.60 ± 0.24 0.90 ± 0.40Total 93p 0.2052 < 0.0001 < 0.0001 < 0.0001 0.0017 < 0.0001 0.0219 0.0005 0.2871

p value indicates level of difference among the age groups. Data are given as mean ± standard deviation.I = wave I, III = wave III, V = wave V, amp = amplitude, IPL = interpeak latency, PL = peak latency.

384 J.J. Luo et al. / Journal of Clinical Neuroscience 20 (2013) 383–388

integrity of the auditory conduction pathways, including theacoustic nerve, brainstem, subcortical and cortical areas relatedto auditory processing, thus assisting to differentiate various sitesof abnormalities involved in children with speech and language de-lays.18–20

However, both BAEP and MLAEP are rarely recorded in routineclinical neurophysiologic studies of hearing and language disordersin children. The purpose of this study is to demonstrate that MLAEPare measurable, along with BAEP, in children from 1 week to3 years of age.

BAEP

38 gestational week

male

2 months

male

6 months

male

10 months

female

Fig. 1. Waveforms showing brainstem auditory evoked potentials (BAEP) and m

2. Methods

2.1. Subjects

The data were collected from our neurophysiology databank viaa retrospective review of clinic charts from January 1 2000 toDecember 31 2002 at St Christopher’s Hospital for Children. Datafor subjects up to 3 years old who had BAEP and MLAEP with iden-tifiable waveforms were collected. Subjects with known abnormal-ities such as a brain or brainstem structural lesion on neurologic

MLAEP

iddle latency auditory evoked potentials (MLAEP) in very young children.

J.J. Luo et al. / Journal of Clinical Neuroscience 20 (2013) 383–388 385

examination and neuroimaging; a history of neurodegenerative,metabolic or congenital disorders; central nervous system (CNS)infections; encephalopathy; and those who had received chemo-therapy were subsequently excluded.

2.2. Recording conditions for auditory evoked potentials

A subset of children who required sedation for the study (onechild under 1 year old, 19 children 1–2 years old and three children2–3 years old) received chloral hydrate 20–50 mg/kg orally. A fewof these children (n = 3) also received 0.2–0.5 mg/kg oral diazepam,when they did not respond to the initial chloral hydrate dose.Administration of these medications has been reported to have

BAEP Interpe

1

2

3

4

5

6

1w 1m 2m 4m 6m

ms

BAEP Am

0

0.2

0.4

0.6

0.8

1

1.2

1w 1m 2m 4m 6m

uV

Fig. 2. Graphs showing evolution of brainstem auditory evoked potentials (BAEP) in dw = week, y = year, I = wave I, III = wave III, V = wave V, amp = amplitude. (This figure is

no significant effects on BAEP and MLAEP.21 Recordings were madewith subjects comfortable in the recumbent position on a bed orseated in an armchair in a semi-darkened room with constant illu-mination intensity.

The BAEP and MLAEP were obtained using a Bravo electroen-cephalograph (Nicolet Biomedical, Madison, WI, USA) and goldcup disk electrodes. Waveforms were recorded with the referenceelectrodes placed at the earlobes A1 and A2, recording at the vertex(Cz), and the ground electrode at the high forehead FPz. Stimula-tion with 100 ms clicks starting with rarefaction polarity was per-formed monaurally with contralateral masking white noise at40 dB. The stimulation frequency was 9.1 Hz for BAEP and 5.1 Hzfor MLAEP. Threshold was determined by the appearance of wave

ak Latency

8m 10m 12m 1.1-2y 2.1-3y

I-IIIIII-VI-V

plitude

8m 10m 12m 1.1-2y 2.1-3y

IampVamp

ifferent measures in young children. The x axis represents child age: m = month,available in colour at www.sciencedirect.com.)

386 J.J. Luo et al. / Journal of Clinical Neuroscience 20 (2013) 383–388

V on audiometry, using a series of clicks at 70, 50, 30 and 10 dBintensity. The stimulation intensity was set at 60 dB above thehearing threshold. Band-pass was set at 100–3000 Hz for BAEPand 30–250 Hz for MLAEP. Four thousand sweeps were averagedand 10 ms were recorded for BAEP, while 1000 sweeps were aver-aged and 70 ms recorded for MLAEP.

2.3. Data acquisition and analysis

For BAEP, the PL of waves I, III and V; IPL of waves I–III, III–V andI–V; the amplitudes of wave I and V; and the ratios of the ampli-tudes of waves V and I (V/I) were measured.

For MLAEP, the PL and amplitude of P0 and Na were defined bywaveform appearance 5–15 ms following stimulus onset withopposite polarity. Pa latency was defined by waveform appearance10–40 ms following stimulus onset with the same polarity as P0.The PL of the individual waves and the IPL between the waves weremeasured. Since the waveforms of Nb and Pb were unreliably re-corded in children younger than the age of 4 years,15,22 they werenot included in this study.

Statistical Analysis System (SAS) software (Cary, NC, USA) wasused to analyze the data. One-way ANOVA was used to evaluatethe difference among age groups for each variable and for the com-parison of the ipsilateral with the contralateral recordings. A valueof p < 0.05 was considered statistically significant.

3. Results

One hundred and thirty-three children up to 3 years of age whohad both BAEP and MLAEP recordings were initially identified. Of

Fig. 3. Graphs showing evolution of middle latency auditory evoked potentials (MLAEP)w = week, y = year, Na = wave Na, P0 = wave P0, Pa = wave Pa. (This figure is available in

these, 93 subjects who fulfilled the inclusion criteria were includedin this study. They were distributed in various age groups from oneweek to 3 years (Table 1).

BAEP and MLAEP could be detected as early as 38 weeks gesta-tional age and became easily recorded after the age of 2 months(Fig. 1).

The PL of waves I, III and V; the IPL of waves I–III, III–V and I–V;the amplitudes of waves I and V; and the ratios of the amplitudesof waves V and I (V/I) for BAEP are shown in Table 1. The individualPL of waveforms I, III and V and the IPL of I–III, III–V and I–V wereobserved to be longer at birth, shortening continuously until theage of 3 years with significant statistical differences (Fig. 2, Table 1).The amplitudes of both wave I and wave V increased with age(p = 0.02 and 0.0005, respectively), however, without significantchange in the ratios of V/I (p = 0.29).

The interlateral measures of PL of P0, Na and Pa, and IPL of P0–Na, Na–Pa and P0–Pa of MLAEP are shown in Fig. 3 and Tables 2and 3. Significant shortening of the PL of P0 and Na and IPL ofP0–Na was also observed with age; however, no significantchanges in Pa latency were observed.

4. Discussion

In this study we demonstrated that MLAEP can be measured inyoung children (Fig. 1). A combination of measurements of BAEPand MLAEP may aid in the neurophysiologic assessment of childrenwith auditory processing disorders and language delays at a youngage. To the best of our knowledge, there are no serial data ofMLAEP in children younger than 2 years reported in the literature.

in different measures in young children. The x axis represents child age: m = month,colour at www.sciencedirect.com.)

J.J. Luo et al. / Journal of Clinical Neuroscience 20 (2013) 383–388 387

In agreement with previous reports on BAEP, our resultsshowed a decrease in PL of waves I, III, and V, in IPL of I–III, III–Vand I–V, and an increase in the amplitude of wave I and V withage (Fig. 2, Table 1).23,24 These changes probably reflect develop-mental hierarchy or the stages of maturation of the CNS. It is wellknown that myelination in the nervous system facilitates conduc-tion velocity.

The waveforms of P0, Na and Pa in MLAEP in young children arehighly reproducible and more readily recordable than previouslyexpected (Fig. 1). These waveforms originate in generators locatedin discrete anatomic locations. Human studies suggest that thegenerators for P0 and Na are likely located in the upper brainsteminvolving the structures of the inferior colliculus and medial genic-ulate body.25,26 It is currently accepted that P0 and Na are gener-ated in the subcortical region while Pa is generated in theauditory cortex.

The PL of P0 and Na and the IPL of P0–Na in MLAEP shortenedwith age in the period of 6–12 months of life (Fig. 3, Tables 2 and3), which may be related to myelination in the brainstem. Theseage-related changes have been well documented in both periphe-ral nerve conduction studies and studies of central nerve conduc-tion of somatosensory evoked potentials (SSEP) and visualevoked potentials (VEP).27–29 Myelination and cytoarchitecturaland axonal maturation are believed to be the key componentsresponsible for these changes.30 Allison and colleagues observeda ‘‘U’’ type of trend in the latencies of SSEP and VEP from a studyon 286 normal subjects aged from 4 to 95 years.31 The early de-crease in the latencies correlated with maturation of myelinationwith age. Significantly increased detectability of both Na and Pa

Table 2Measures of peak latency in middle latency auditory evoked potentials

Upper limit of age group P0-i P0-c Na-

1 week 8.01 ± 1.51 8.02 ± 1.00 14.21 month 7.85 ± 3.58 9.96 ± 1.71 15.62 months 7.17 ± 0.36 8.20 ± 0.45 12.4 months 7.06 ± 0.51 8.36 ± 0.74 12.46 months 6.96 ± 0.32 7.50 ± 0.34 11.8 months 6.72 ± 0.24 7.79 ± 0.66 11.10 months 6.58 ± 0.42 7.37 ± 0.35 11.412 months 8.33 ± 3.32 8.38 ± 2.48 12.2 years 7.01 ± 2.03 7.70 ± 1.87 11.3 years 6.51 ± 1.53 6.87 ± 0.59 9.9

p (1) 0.7945 0.0136 0.00p (2) 0.004

p (1) value indicates level of difference among the age groups. p (2) value indicates levelData are presented as mean ± SD. c = contralateral, i = ipsilateral, Na = wave Na, P0 = wa

Table 3Measures of interpeak latency in middle latency auditory evoked potentials

Upper limit of age group P0–Na-i P0–Na-c Na–

1 week 6.24 ± 2.35 6.72 ± 2.10 6.1 month 6.67 ± 1.21 6.84 ± 1.71 8.2 months 5.73 ± 1.58 6.89 ± 1.54 9.4 months 5.40 ± 1.55 6.00 ± 0.97 12.6 months 4.44 ± 1.32 5.64 ± 0.84 11.8 months 4.48 ± 1.15 4.57 ± 1.06 8.10 months 4.85 ± 2.59 5.41 ± 2.36 8.12 months 3.71 ± 0.81 5.09 ± 0.43 8.2 years 4.29 ± 1.58 5.19 ± 2.05 9.3 years 3.40 ± 0.52 4.64 ± 1.89 9.

p (1) 0.001 0.0957 0.53p (2) 0.0012

p (1) value indicates level of difference among the age groups. p (2) value indicates levelData are presented as mean ± SD. c = contralateral, i = ipsilateral, Na–Pa = interpeak latenc

in MLAEP has been observed as a function of age in children.15,22

In agreement with those reports, our study confirms the evolutionin BAEP and MLAEP with increasing age in young children.

Measurement of the Pa latency and P0–Pa IPL can provide infor-mation on the integrity or functional status of auditory processingin the subcortical and cortical areas. However, it may be age lim-ited because of the absence of Nb and Pb in MLAEP before theage of 4 years.15,22 Interestingly, the IPL of P0–Pa and Na–Pa werefound to be initially prolonged with ageing (Fig. 3, Table 3) whichmight be due to a hierarchy of acoustic synaptic maturation in theauditory cortex or, alternatively, increase in the distance of thepathway paralleled to increase in cephalic size. An additionalexplanation is that acquisition of development may be diverselydistinct in different segments of the auditory pathway within thebrainstem, acoustic cortex and/or its adjacent subcortical whitematter. The observation that waveforms of Nb and Pb could notbe recorded in early life, but become reliably evoked after theage of 4 years, supports this notion.15,22

Multiple pathophysiologic conditions may affect MLAEP record-ings. The amplitude of MLAEP waveforms may vary significantlydepending on the subject’s age, medication and functional sta-tus.15,22,32–35 Changes in body temperature, stimulation or record-ing paradigm can also influence the recordings.36–39 Prolonged Palatency is seen in the elderly.40 Of note, these results are all fromstudies conducted in adults. Whether the effects of those factorson MLAEP in young children are the same as in adults remains tobe elucidated. Therefore, it is recommended that individual neuro-physiologic laboratories should establish their own normative databased on their recording conditions.

i Na-c Pa-i Pa-c

5 ± 3.81 14.74 ± 2.84 20.69 ± 2.98 21.28 ± 3.413 ± 2.92 16.80 ± 1.86 23.80 ± 2.12 23.37 ± 3.08

90 ± 1.60 15.09 ± 1.49 22.50 ± 2.97 23.15 ± 2.826 ± 1.21 14.36 ± 1.08 24.30 ± 4.50 25.02 ± 3.36

40 ± 1.59 13.14 ± 1.12 23.12 ± 3.46 21.56 ± 1.8620 ± 1.38 12.37 ± 1.47 19.60 ± 0.85 20.85 ± 1.04

3 ± 2.96 12.79 ± 2.63 19.83 ± 0.40 20.58 ± 1.9604 ± 3.02 12.95 ± 1.46 20.67 ± 3.41 19.25 ± 1.4630 ± 2.78 12.90 ± 2.39 20.66 ± 4.95 20.82 ± 4.72

1 ± 1.91 11.51 ± 2.22 19.80 ± 6.99 20.76 ± 6.31

24 0.0002 0.4965 0.43120.0003 0.8294

of difference between the ipsilateral and contralateral measures of the age groups.ve P0, Pa = wave Pa.

Pa-i Na–Pa-c P0–Pa-i P0–Pa-c

44 ± 2.30 6.55 ± 1.30 12.68 ± 1.78 13.26 ± 2.4517 ± 2.03 6.24 ± 2.78 14.84 ± 1.48 13.15 ± 1.7459 ± 2.44 8.42 ± 2.33 15.32 ± 2.89 14.89 ± 2.6401 ± 3.82 10.86 ± 2.69 17.22 ± 5.01 16.92 ± 3.4592 ± 2.29 8.65 ± 1.09 16.15 ± 3.23 14.07 ± 1.6940 ± 2.22 8.48 ± 1.21 12.88 ± 1.09 13.05 ± 1.2840 ± 2.55 7.79 ± 2.14 13.25 ± 0.21 13.21 ± 1.6263 ± 4.84 7.09 ± 1.69 12.34 ± 4.52 12.17 ± 1.7432 ± 4.46 7.90 ± 3.67 13.62 ± 4.78 13.02 ± 4.6980 ± 6.60 9.42 ± 6.46 13.16 ± 6.65 14.11 ± 6.46

77 0.5894 0.6032 0.71030.0651 0.5545

of difference between the ipsilateral and contralateral measures of the age groups.y of Na–Pa, P0–Na = interpeak latency of P0–Na, P0–Pa = interpeak latency of P0–Pa.

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Abnormalities of either disappearance of the individual wave-forms or delay in PL and/or IPL indicate abnormalities involvingeither the generator and/or the relevant fibers in the auditoryconduction pathways. Measurement of MLAEP may assist in iden-tifying hearing dysfunction secondary to subcortical lesions, spe-cifically involving the quadrigeminal plate or the diencephalon,in the presence of a normal BAEP.20 Therefore, measurement ofMLAEP, along with the BAEP, may increase the sensitivity of neuro-physiologic diagnoses.

In conclusion, our findings demonstrated that MLAEP are mea-surable in young children, including those younger than 1 year ofage. Use of the MLAEP, along with the BAEP, may increase the diag-nostic sensitivity in neurophysiologic assessment of the integrityor functional status of both the peripheral (acoustic nerve) andthe central (brainstem, subcortical and cortical) auditory conduc-tion systems of young children with developmental speech andlanguage disorders.

Acknowledgments

The authors thank the staff at the Section of Neurology, Depart-ment of Pediatrics, St. Christopher’s Hospital for Children for theirhelp and support in data collection, and Jie Feng, PhD, for statisticalassistance.

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