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 »  Introduction
 »  Material and methods
 »  Results
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Year : 2001  |  Volume : 49  |  Issue : 1  |  Page : 51-4

Brainstem auditory evoked potentials in tubercular meningitis and their correlation with radiological findings.

Department of Neurology, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow - 226014, India.

Correspondence Address:
Department of Neurology, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow - 226014, India.

  »  Abstract

The present study has been undertaken to describe brainstem auditory evoked potential (BAEP) changes in tubercular meningitis (TBM) and correlate these with CT scan and MRI findings. 24 patients with TBM were subjected to clinical evaluation and CT scan or MRI study. Outcome was defined by 3 month Barthel index score (BI) into poor (BI<12) and good (BI>or=12). The mean age of patients was 26.4+/-14.9 (range 10-62) years, 8 of them were females. Sixteen patients were in stage III, 5 in stage II and 3 in stage I meningitis. CT scan revealed hydrocephalus in 16, exudate in 9, infarction in 12 and tuberculoma in 3 patients. Brainstem was involved in 3 patients (2 infarction and 1 granuloma). BAEPs were unrecordable in one patient and abnormal in 15. The absolute latencies and inter peak latency (IPL) however were not significantly affected. The wave V/I amplitude ratio was abnormal on 12 sides. The BAEP abnormalities were not related to the stage of meningitis, level of consciousness, any specific CT or MRI changes or outcome at 3 months.

How to cite this article:
Kalita J, Misra U K. Brainstem auditory evoked potentials in tubercular meningitis and their correlation with radiological findings. Neurol India 2001;49:51

How to cite this URL:
Kalita J, Misra U K. Brainstem auditory evoked potentials in tubercular meningitis and their correlation with radiological findings. Neurol India [serial online] 2001 [cited 2023 Mar 21];49:51. Available from: https://www.neurologyindia.com/text.asp?2001/49/1/51/1301

   »   Introduction Top

Tubercular meningitis (TBM) differs from pyogenic
and viral meningitis by predominant basal
involvement, associated granuloma formation,
vasculitis, infarction and hydrocephalus.[1],[2] These
associated pathologies may affect the brainstem
functions. Brainstem auditory evoked potential
(BAEP) studies may provide objective noninvasive
documentation of these functions. BAEP studies have
been extensively conducted in pyogenic meningitis
for monitoring hearing loss.[3],[4],[5],[6] We could not get any
report of BAEP changes in TBM in the literature. In
the present communication, results of BAEP have
been correlated with clinical and radiological

   »   Material and methods Top

Patients with TBM seen between 1996 and 1998 were
included in this study. All the patients underwent a
detailed neurological evaluation. Consciousness was
assessed by Glasgow coma scale (GCS), muscle
power by Medical Research Council scale and muscle
tone by Ashworth scale.[7] In comatose patients,
oculocephalic reflex was noted.
Plain and contrast enhanced cranial CT with 10 mm
cuts was done in all cases. Cranial MRI was carried
out on 2T scanner operating at 1.5T, (Magnetome SP
Siemens, Germany). T1WI, proton density and T2
weighted spin echo sequences were obtained.
Presence of hydrocephalus, infarction, exudate and
tuberculoma were noted. The diagnosis of TBM was
based on clinical, CT scan and CSF criteria.7 The
clinical criteria included fever, headache and neck
stiffness for more than 2 weeks. The supporting
evidences were obtained from CSF cells (0.02x109/L
or more, with lymphocytic predominance), proteins
(more than 1 gm/L), sterile bacterial and fungal
culture and CT scan findings for the presence of
hydrocephalus and exudate. Evidence of tuberculosis
outside the central nervous system and response to
antitubercular therapy were noted. In the CT scan,
presence of tuberculoma and infarction were
recorded. The diagnostic categories included (i)
highly probable: clinical and 3 supportive criteria;
(ii) probable: clinical and 2 supportive criteria and
(iii) possible: clinical and one supportive criteria.[8] The
severity of TB meningitis was graded into stage I :
meningitis only, stage II : meningitis and neurological
signs and stage Ill : meningitis, neurological signs
with altered sensorium.[9]
Brainstem auditory evoked potentials (BAEP) : BAEP
were recorded with 0.1 ms rarefaction click
stimulation delivered monaurally at 95 dB. A uniform
stimulus strength was used in all the patients because
most of our patients had altered sensorium. The
stimuli were delivered at a rate of 10 Hz. 2048
responses were twice averaged with a bandpass filter
of 100Hz-3kHz.[10] The latencies of different waves
and interpeak latencies (IPL) of I-III, I-V and III-V
were measured. The results were compared with
control values obtained from 30 healthy volunteers,
whose age ranged between 15 and 68 years. The upper
limit of normal was defined as mean+2.5 SD of
control. The amplitude ratio of wave V/I was also
calculated and considered abnormal if it was below 1.
The clinical and radiological parameters were
correlated with BAEP findings. The recovery was
defined on the basis of 3 month Barthel index score
(BI) into good (BI>12) or poor (BI< 12).[11]

   »   Results Top

Twenty four patients of TBM were included in this
study. Their mean age was 26.4+14.[9] (range 10-62)
years. Eight of them were females. Sixteen patients
were in stage Ill, 5 in stage II and 3 in stage I
meningitis. Their mean GCS score was 10.8+4.2.
Cranial nerves were involved in 12 patients; optic
nerve in 5 and partial or complete external
ophthalmoplegia in 7 patients. In patients with stage I
and II meningitis, bedside hearing tests were normal.
Focal weakness was present in 17 patients which
included quadriplegia in 10, hemiplegia and
paraplegia in 3 each and monoplegia in one patient.
Cranial CT scan was carried out in all and MRI in 15
patients. Cranial CT scan revealed exudate in 9,
hydrocephalus in 16, infarction in 12 and tuberculoma
in 3 patients. The infarctions were located mostly in
basal ganglia. Brainstem infarction was present in 2
patients only; crus cerebri was involved in 1 and right
pontomedullary region in the other. MRI scan was
done in 15 patients and revealed additional findings in
8, which included a midbrain granuloma in 1. The
MRI in remaining patients revealed supratentorial
Brainstem auditory evoked potentials were
unrecordable in one and recordable in 23 patients.
These were abnormal in 15 of them. The absolute
latency of BAEP waveforms was normal in most
patients [Figure - 1] except in 3 sides where wave III
latency was prolonged. Interpeak latency of I-III was
prolonged in 3 sides. Wave V and III were not
recordable in 1 and 3 sides respectively. The group
difference between absolute latency of waveforms and
IPL between TBM patients and controls was not
significant. The mean and SD of various BAEP
waveforms and IPLs in TBM patients and controls are
shown in [Table I]. The V/I amplitude ratio was
abnormal in 12 sides, however, the group differences
were not significant (Z=-1.43).
BAEP and clinicoradiological correlation : The
BAEP abnormalities in 15 patients, did not correlate
with stage of meningitis (X2=0.04, df=2 NS) and level
of consciousness (X2=0.94, df=2 NS). Out of 3
patients in stage I meningitis, BAEP was abnormal in
2, whereas out of 16 patients with stage III meningitis,
it was abnormal in 10 patients. The BAEP
abnormalities also did not correlate with 3 month
outcome (X2=0.10, df=1 NS). At 3 month followup, 6
patients had good and 14 had poor outcome. CT scan
abnormalities also did not significantly correlate with
BAEP abnormalities. Hydrocephalus was present in
16 patients, 10 of these patients had abnormal BAEP
and 8 of whom had abnormal V/I amplitude ratio. The
other abnormalities in the patients with hydrocephalus
included abnormal wave II in 1, wave III in 6, wave V
in 1, I-Ill IPL in 4, III-V IPL in 2 and I-V IPL in 1
patient. Presence of hydrocephalus, however, did not
correlate with BAEP abnormality (X2=0.20, df=1,
NS). One patient had lateral pontomedullary
infarction in whom wave III and V were unrecordable.
The other patient had infarction of midbrain and crus
and his wave V/I amplitude ratio was abnormal. The
distribution of radiological changes in patients with
abnormal BAEP are summarised in [Table II].

   »   Discussion Top

In this study, BAEP was abnormal in 16 out of 24
patients with TBM. The abnormalities included
reduction of wave V/I amplitude ratio, prolongation of
I-III IPL; absence of wave III and V; however, the
group difference was not significant. The reduction of
wave V/I amplitude ratio was the commonest
abnormality, and was present in 11 patients. The
amplitude reduction may be due to raised intracranial
tension (ICT) which often accompanies TBM.
Presence of hydrocephalus in 8 patients with V/I
amplitude reduction further supports the possibility of
raised ICT, although intracerebral pressure monitoring
was not undertaken. Reduction of wave V/I amplitude
ratio has also been reported in supratentorial space
occupying lesion resulting in upper brain stem
compression in cats.[12] It has been shown that
mechanical compression of upper brainstem causes
interference with brainstem circulation. In our study,
2 patients had brainstem infarction. BAEP was
abnormal in both. Wave V/I amplitude ratio reduction
was seen in 1 and unrecordable wave Ill and V in the
other. BAEP has been reported to be useful in
monitoring brainstem ischaemia and impending
brainstem stroke respectively in patients presenting
with vertigo.[13],[14],[15] The BAEP abnormalities are
common in the acute stage compared to recovery
period.13 Vasculitis, although common in TBM, may
be seen in 20.5-55% patients depending on the
method of evaluation,[15],[16] but is reported to be rare in
vertebrobasilar territory.[1],[17] The infarctions are
usually present in supratentorial perforating vessels
affecting basal ganglia, thalamus and internal capsular
region. In our study, basal ganglionic and capsular
infarctions were present in 10 and brainstem stroke in
2 patients only.
Prolongation of wave I-III IPL was noted in 3 patients.
It suggests abnormality in proximal part of VIII nerve
to pontomedullary junction or lower pons around
superior olive or trapezoid bodies.[18] The midbrain
granuloma was seen in one of our patients in whom
wave III was unrecordable. On analysing the CT scan
with prolonged I-III IPL, miliary granuloma,
hydrocephalus with thalamic and capsular infarctions
and hydrocephalus with supratentorial granuloma was
present in one patient each. Presence of basal exudate
may also result in I-III IPL prolongation. The diversity
of BAEP abnormalities and lack of specific pattern
may be due to diversity of pathophysiological
mechanisms in TBM e.g. in the same patient
hydrocephalus, infarctions, tuberculoma and varying
degree of raised intracranial pressure (ICP) may be
present in various combination at different stages of
meningitis. Most of our patients were in stage III,
therefore, the correlation of hearing deficit with BAEP
changes was not possible. In bacterial meningitis,
BAEP studies have been used to monitor the hearing
From this study, it can be concluded that although
BAEP abnormalities are frequent in TBM but are
probably nonspecific and mostly in the form of
reduced V/I amplitude ratio. Further studies are
needed including CSF pressure monitoring to evaluate
the role of ICP on BAEP changes and possible
reversibility of these changes after manoeuvers
reducing ICP in TBM.

  »   References Top

1.Bhargava S, Gupta AK, Tendon PN : Tuberculous meningitis : A CT scan study. Br J Radiol1982; 55 : 189-196.  Back to cited text no. 1    
2.Dastur DK, Lalitha VS, Udani PM et al : The brain and meninges in TBM : gross pathology in 100 cases and pathogenesis. Neurol India1970; 18 : 86-100.  Back to cited text no. 2    
3.Bao X, Wong V : Brainstem auditory evoked potential evaluation in children with meningitis. Pediatr Neurol 1998;19 : 109-112.  Back to cited text no. 3    
4.Duclus R, Sevin F, Ferver C et al : Brainstem auditory evoked potentials following meningitis in children. Brain Dev 1993;15 : 340-345.  Back to cited text no. 4    
5.Jiang ZD, Liu XY, Wu YY et al : Longterm impairments of brain and auditory function of children recovered from purulent meningitis. Dev Med Child Neurol 1990; 32 : 473-480.  Back to cited text no. 5    
6.Vienny H, Despland PA, Lutschg J et al : Early diagnosis and evolution of deafness in childhood bacterial meningitis: A study using brainstem auditory evoked potentials. Pediatrics 1984; 73 : 579-586.  Back to cited text no. 6    
7.Penn RD, Savoy SM, Corios D et at : Intrathecal baclofen for severe spinal spasticity. N Engl J Med1989; 320 : 517-521.  Back to cited text no. 7    
8.Shankar P, Manjunath N, Mohan KK et al : Rapid diagnosis of tuberculosis meningitis by polymerase chain reaction. Lancet1991; 337 : 5-7.  Back to cited text no. 8    
9.Lincoln EM, Sordillo SVR, Davics PA : Tuberculous meningitis in children. J Pediatr 1960; 57 : 807-810.  Back to cited text no. 9    
10.Klockgether T, Petersen D, Grodd W et al : Early onset cerebellar ataxia with retained tendon reflexes: clinical electrophysiological and MRI observations in comparison with Friedreich's ataxia. Brain 1991; 114 : 1559-1573.  Back to cited text no. 10    
11.Kalita J, Misra UK : Brainstem auditory evoked potentials in Japanese encephalitis. J Neurol Sci 1999; 165 : 24-27.  Back to cited text no. 11    
12.Goodman SJ, Becker DP : Vascular pathology of brainstem due to experimentally included intracranial pressure changes noted in micro and macro circulation. J Neurosurg 1973; 39: 601-609.  Back to cited text no. 12    
13.Drake MEJR, Pakalris A, Pdamadan H et al : Auditory evoked potentials in vertibrobasilar transient ischaemic attacks. Clin Electroencephalogr 1990; 21 : 96-100.  Back to cited text no. 13    
14.Ferbert A, Bushner H : Evoked potentials in diagnosis of ischaemic lesions. Nervenarzt 1991; 62 : 460-466.  Back to cited text no. 14    
15.Rao TH, Libman IB : When is isolated vertigo a harbinger of stroke. Ear Nose Throat J 1995; 74 : 33-36.  Back to cited text no. 15    
16.Wang Z : Study of brainstem auditory evoked potentials in patients with insufficient vertebrobasilar blood supply. Chung Hue Shen Chiang Chiang Shen Ko Tsa Chih 1992; 25 : 41-43.  Back to cited text no. 16    
17.Sood S, Mahapatra AK : Effect of CSF shunt on brainstem auditory evoked potential in hydrocephalus secondary to brain tumour. Acta Neurochir 1991; 111 : 92-95.  Back to cited text no. 17    
18.Gupta RK, Gupta S, Singh D et al : MR imaging and angiography in tuberculous meninigitis. Neuroradiology 1994; 36 : 87-92.  Back to cited text no. 18    


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