Brainstem auditory evoked potential abnormalities in myelomeningocoele in the older child

Prognostic value of newborn hearing screening in patients with myelomeningocele

OBJECT

Brainstem dysfunction occurs in a minority of patients with myelomeningocele (MMC), most of whom have Chiari Type II malformation. Some surgeons advocate early identification of these patients for craniocervical decompression to avoid significant mortality. The auditory brainstem response has been found to be abnormal in most children with MMC. The present study examines whether failure of routine newborn hearing screening (NHS) predicts brainstem dysfunction in MMC patients.

METHODS

The charts of 40 newborns with MMC and 50 newborns without MMC who stayed in the neonatal intensive care unit were reviewed. Results of NHS, brainstem symptoms, birth demographics, and surgical history were retrospectively examined. Differences in the presence and onset of brainstem symptoms by NHS result were assessed.

RESULTS

Failure of NHS was more common among newborns with MMC who developed brainstem symptoms (31%, 4 of 13 patients) than among newborns without MMC (0%, 0 of 50 patients; p = 0.001). Among the 40 newborns with MMC, brainstem symptoms were more common in those who failed NHS (80%, 4 of 5 patients) than in those who passed (26%, 9 of 35 patients; p = 0.031). Respiratory symptom onset occurred later in patients who failed NHS (median 16 months) than among those who passed (median 0 months; p = 0.022). The positive and negative predictive values of NHS for brainstem dysfunction in MMC were 0.80 and 0.74, respectively.

CONCLUSIONS

Results of NHS may help predict future brainstem dysfunction in patients with MMC and may be useful to incorporate into prognostic assessment and surgical decision making.

[Chiari II malformation. Supportive and predictive value of brainstem reflex and EAEP recordings]

BACKGROUND

In about 20% of patients with Chiari II malformation brainstem signs and symptoms occur. Ventilatory dysfunction is the main cause of death in these patients. The indication for craniocervical decompression is based on clinical examination because supporting electrophysiological or radiological methods were lacking.

METHODS

In a prospective study the clinical courses of 106 patients were documented during a 3-year period. In addition brainstem diagnostic procedures using the masseter reflex (MR), blink reflex (BR) and early auditory evoked potentials (EAEP) were done. Based on the model of binary logistic regression the odds ratio (OR) of progression over time was calculated.

RESULTS

The combination of MR and late BR components showed the highest correlation with clinical findings (OR: 23). The highest predictive value regarding clinical progression over a 3-year period was shown by the combined evaluation of MR, late BR components and EAEP interpeak latency I-V (OR: 17.6). Signs and symptoms had no predictive value.

CONCLUSIONS

Combined brainstem reflex recordings (MR and late BR components) support the clinical examination. To evaluate the long-term prognosis brainstem reflexes and EAEP recordings should be used.

Somatosensory evoked potentials in Arnold-Chiari malformation

Nearly all patients with repaired myelomeningoceles have an Arnold-Chiari (AC) malformation and about 20% of these patients develop clinical signs of brainstem dysfunction. The management of symptomatic AC malformation is still controversial and techniques are needed to provide an objective assessment of brainstem function. We recorded somatosensory evoked potentials (SEPs) in 52 patients aged between 8 months and 20 years (median 7.3 years) with AC malformation, to determine whether the SEPs discriminate patients with symptomatic AC malformation from those without symptoms. The subcortical far-field components P13, P14 and N18, which are generated within the brainstem, were recorded with non-cephalic reference electrodes and the cortical N20 with a frontal reference. Fourteen patients (27%) had signs and symptoms of brainstem dysfunction, which were related to the AC malformation. Abnormal SEPs were mainly recorded in symptomatic patients (sensitivity 0.7, specificity 0.9). The SEPs were particularly useful in patients from 4 years of age (sensitivity 0.9, specificity 0.9), but not in the younger age group. Abnormal somatosensory conduction reflects dysfunction of the brainstem or the upper cervical cord and may be clinically useful to assess patients with late onset symptomatic AC malformation.

Masseter reflex and blink reflex abnormalities in Chiari II malformation

Masseter reflex and blink reflex were evaluated in 64 patients with a myelomeningocele and Chiari II malformation. In 46 patients, no brainstem signs or symptoms were present. Brainstem dysfunction related to Chiari II malformation occurred in 18 patients. The masseter reflex was more frequently abnormal in the symptomatic than asymptomatic patients (P = 0.02). Although the blink reflex was similarly affected in the two groups of patients (P > 0.1), it was very sensitive, being abnormal in 83% of symptomatic and 65% of asymptomatic patients. Concomitant abnormality of masseter reflex and the late contralateral blink reflex component (R2c) was almost exclusively found in symptomatic patients and reached the highest significance in separating the two groups (P = 0.002).

Assessment of brainstem function in Chiari II malformation utilizing brainstem auditory evoked potentials (BAEP), blink reflex and masseter reflex

Brainstem dysfunction was evaluated in 67 patients with myelomeningocele and Chiari II malformation using brainstem auditory evoked potentials (BAEP), blink reflex (BR) and masseter reflex (MR). Signs and symptoms related to Chiari II malformation were observed in 18 patients while 49 patients had normal brainstem findings. BAEP and BR showed a higher sensitivity of brainstem involvement than MR (BAEP=1.0, BR=0.83, MR=0.50). BR, and in particular, MR were of higher accuracy (BR=0.52, MR=0.72) than BAEP (0.39) in separating patients with brainstem signs and symptoms related to Chiari II malformation. We feel that this is due to anatomic and physiologic peculiarities of the brainstem structures mediating BR and MR. Our results suggest that brainstem reflexes can support the decision of further treatment.

Brainstem auditory and visual evoked potentials in infants with myelomeningocele

Brainstem auditory evoked potentials (BAEPs) and visual evoked potentials (VEPs) were recorded in 47 infants with myelomeningocele to determine if the evoked potentials reflected the early neurological status, and if they had prognostic value as to the children's neurological outcome. The infants were tested between 1 day and 3 months of age (mean 24 days), while still in hospital after the myelomeningocele repair. Outcome was assessed at a mean of 2 years of age. Normal BAEPs were found in 41% and normal VEPs in 62% of the patients. BAEPs were abnormal in all infants studied who had symptomatic Arnold-Chiari (AC) malformation (n = 9); VEPs were abnormal in only 55% of symptomatic infants. Of the infants who did not have symptomatic AC malformation, 53% had normal BAEPs, 69% had normal VEPs. Of the patients with normal BAEPs, 81% had normal cerebral function on follow-up. Of the patients with abnormal BAEPs, 87% had central neurological abnormalities on follow-up. Of the patients with normal VEPs, 63% were normal on follow-up; of the patients with abnormal VEPs, 71% were abnormal on follow-up. Thus, the VEPs studied early in the neonatal course do not appear to be sufficiently sensitive to be valuable prognostically in these infants. However, the BAEPs were consistently abnormal in symptomatic AC malformation and showed a positive predictive value of 88% and an accuracy in predicting central neurological sequelae of 84%.

Blink reflex in meningomyelocele, with special reference to its usefulness in the evaluation of brainstem dysfunction

The electrically elicited blink reflex (BR) was studied in 30 patients with meningomyelocele (MMC), including 21 with Chiari type II malformation. The relationship between the BR and brainstem auditory evoked potentials (BAEPs) is discussed with regard to its usefulness in the evaluation of MMC's brainstem dysfunction. The following results were obtained: (1) The R2 component was abnormal in 90% of these patients. The BR disclosed subclinical lesions in the medulla oblongata which were not detected by BAEPs alone. (2) In all patients in whom the BAEPs suggested the presence of stretched cochlear nerves, the BR indicated the existence of some dysfunction of the medulla oblongata. (3) No close relationship was found between the dysfunction detected by the BR and the degree of hindbrain anomaly on the neuroimaging. (4) Combining results from assessment of the measurement of the BR and BAEPs permits evaluation of the function of the fifth, seventh, and eighth cranial nerves, as well as the brainstem including the medulla oblongata, which is more comprehensive than evaluation by neuroimaging alone.

BAEPs in infants with myelomeningocele and later development of Chiari II malformation-related brainstem dysfunction

Thirty-seven infants with myelomeningocele received brainstem auditory evoked potentials (BAEPs) at a median age of eight days. No infant had brainstem dysfunction at the time of testing. Median follow-up was at 30 months. Of 12 infants who subsequently developed brainstem dysfunction at a median age of three months, 11 had had abnormal neonatal BAEPs. In contrast, only 10 of 25 infants who did not develop brainstem dysfunction had abnormal BAEPs. The mean average I-V interpeak latencies was greater among those who developed symptoms than among those who did not. Neonatal BAEPs can identify a group of asymptomatic infants with myelomeningocele who need close follow-up for the subsequent development of brainstem dysfunction.

The prevalence of neurologic dysfunction in children with strabismus who have superior oblique overaction

BACKGROUND

Children with certain neurologic diseases (hydrocephalus, meningomyelocele, or cerebral palsy) have been reported to manifest a high frequency of A-pattern strabismus and superior oblique overaction. However, it is not generally recognized whether children with strabismus who have superior oblique overaction are more likely to have concurrent neurologic diseases than those without superior oblique overaction. In this study, the authors examine this issue.

METHODS

The authors retrospectively reviewed the medical records of all patients (n = 168) with overdepression of the downturned eye in adduction, who were examined between October 1989 and March 1992. A randomly selected population of children with strabismus who did not have overdepression of the eye on infraduction and adduction served as controls (n = 98). Patients with simulating or confounding conditions such as pseudo-superior oblique overaction, inferior rectus skew deviation (alternating skew on lateral gaze), and restrictive or paralytic strabismus, and who were older than 20 years of age, were excluded.

RESULTS

One hundred twelve patients with true superior oblique overaction were analyzed. Of these 112 patients, 45 (40.2%) had concurrent neurologic abnormalities, compared with less than one fifth (17.3%) of control subjects (17 of 98) (P < or = 0.001).

CONCLUSIONS

Children with strabismus who have superior oblique overaction were found to have higher prevalence of concurrent neurologic diseases than control subjects. Superior oblique overaction may represent a clinical marker for an associated neurologic dysfunction, possibly representing a form of skew deviation in some cases.

Alternating skew on lateral gaze. Neuroanatomic pathway and relationship to superior oblique overaction

BACKGROUND

Previous studies of patients with heterogeneous, often diffuse neurologic disorders concluded that the neurologic substrate for alternating skew on lateral gaze may be localized at the level of the brain stem tegmentum or the cervico-medullary junction, or both. The localized nature of brain tumors offers an opportunity to further investigate the anatomic localization for this as well as other conditions.

METHODS

To test the hypothesis that cervico-medullary and cerebellar lesions are responsible for alternating skew on lateral gaze, the authors investigated a series of 50 children with brain tumors, 39 of whom showed neuro-ophthalmologic abnormalities on clinical testing. Seven children had alternating skew on lateral gaze.

RESULTS

All seven children with alternating skew on lateral gaze showed neoplastic involvement at the level of the cervico-medullary junction and/or the cerebellum on critical analysis of neuro-imaging studies.

CONCLUSION

The authors conclude that the neuroanatomic substrate for alternating skew on lateral gaze is localized at the level of the cervico-medullary junction and/or the cerebellum. Knowing that (1) alternating skew on lateral gaze closely mimics superior oblique overaction clinically, (2) superior oblique overaction is frequently found in patients with myelomeningocele, and (3) myelomeningocele is uniformly associated with Arnold-Chiari type II which includes cerebellar and cervico-medullary region abnormalities, the authors propose that alternating skew on lateral gaze and superior oblique overaction associated with myelomeningocele have similar neuroanatomic pathways.

Evoked potentials in infant brainstem syndrome associated with Arnold-Chiari malformation

This study evaluated the contribution of brainstem auditory evoked potentials (BAEPs) and median nerve somatosensory evoked potentials (SEPs) to the assessment of brainstem dysfunction in infants with myelomeningocele and Arnold-Chiari malformation. 16 infants under one year of age were studied. Six had infant brainstem syndrome (IBS). 11 had abnormally prolonged I-V interwave latency (brainstem transmission time, BSTT); BSTT did not differentiate those patients with and without IBS. The cortical 'N20' component of the median-nerve SEPs was absent or had low amplitude and prolonged latency in all six patients with clinical signs of brainstem dysfunction and in four without. Median-nerve SEPs were normal in the patients without IBS. There was a significant difference between patients with and without IBS. Median-nerve SEPs may be a helpful measure of brainstem function in infants with Arnold-Chiari malformation.

Neuro-ophthalmological findings in relation to CNS lesions in patients with myelomeningocele

Twenty-eight patients (14 male, 14 female; aged four to 34 years) with myelomeningocele were studied. Magnetic resonance imaging was used to determine the correlation between disturbances of ocular motility and the degree of hydrocephalus, tectal plate deformity and dislocation of the cerebellum and medulla oblongata. All patients had Chiari malformations. Strabismus and spontaneous nystagmus were strongly related mainly to the degree of hydrocephalus and to some extent to the amount of lower brainstem deformities. Ocular motility defects with regard to oblique muscle functions and horizontal and vertical gaze and saccadic control often correlated with lower brainstem lesions. Convergence defects correlated with deformities of the upper brainstem. However, these correlations were not valid in the individual patient; some had no strabismus and normal ocular motility, in spite of advanced hydrocephalus and Chiari malformations.