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Auditory fiber crossing.

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LETTERS
Brainstem Auditory
Evoked Responses
and Palatal Myoclonus
Cause of AER Abnormalities
It seems risky to place in print conclusions about
neuroanatomical crossing of fiber tracts and location of lesions based only on clinical examination, without autopsy
or surgical confirmation.
4440 Broadway
Kansas City, M O 641 11
S. Gothgen, MD, L. Jacobs, MD, and R. P. Newman, MD
Reply
The title of the recent article by Epstein, Stappenbeck, and
Karp [l] is misleading, as it implies that the pathological
mechanism producing palatal myoclonus is somehow also
responsible for abnormal auditory evoked responses
(AERs). The anatomical correlate of palatal myoclonus is
pseudohypertrophy of one o r both of the inferior olivary
nuclei-all cases of palatal myoclonus that have come to
autopsy have shown this pathological change [ 3 ] . Usually
the olivary changes are associated with other brainstem involvement, as was indicated by the clinical picture of their
patient, who had nystagmus, right hemiataxia, and left
hemisensory loss in addition to the palatal myoclonus.
Since the inferior olivary nuclei are not components of
the brainstem auditory pathways, it would seem logical to
assume that the AER abnormalities observed in the patient
reported by Epstein and associates were due to his extraolivary brainstem involvement. W e recently confirmed
in two patients with isolated palatal myoclonus (i.e., no sign
of brainstem involvement other than palatal myoclonus),
both of whom had normal AERs, that inferior olivary lesions d o not produce AER abnormalities [ 2 ] .
The AER findings of Epstein and associates support the
concept of auditory crossing in the brainstem, and this observation deserved being featured in their title.
Charles M. Epstein, MD, Richard Stappenbeck, MD,
and Herbert R. Karp, MD
Drs Gothgen, Jacobs, and Newman appear to believe that
the primary lesion in palatal myoclonus is at the inferior
olive. Pseudohypertrophy of the inferior olive is, however,
merely a secondary change. The primary lesion appears to
lie more rostrally, most often in the central tegmental tract
on the ipsilateral side [ 1, 21. This localization correlates
well with the other findings in our patient.
The questions raised by Dr Whittaker are appropriate. A
more detailed discussion of these issues was deleted from
the original manuscript for reasons of space. Some observers may feel that a residual wave V is present in Figure B;
if so, it remains abnormal by both latency and amplitude
criteria.
W e disagree with the assertion that clinical localization is
necessarily dangerous. Our patient certainly has a lesion of
the right brainstem; what we cannot absolutely exclude is a
clinically silent lesion o n the other side. However, the systems involved on the right pass very near to the lateral
lemniscus. The evidence is circumstantial, but we think it is
at least suggestive until better data are available.
Dent Neurologic Institute
Bnflalo, N Y 14209
Department of Neurology
Emory University School of Medicine
Atlanta, GA 30322
References
References
1. Epstein CM, Stappenbeck R, Karp HR: Brainstem auditory
evoked responses in palatal myoclonus. Ann Neurol 7:592,
1980
2. Jacobs L, Newman RP, Bozian D: Disappearing palatal rnyoclonus. Neurology 1980 (in press)
3. Lapresle J, Hamida MB: The dentato-olivary pathway:
somatopic relationship between dentata nucleus and contralatera1 inferior olive. Arch Neurol 22:135-143, 1970
1. Gautier JC, Blackwood W: Enlargement of the inferior olivary
nucleus in association with lesions of the central tegrnental tract
or dentate nucleus. Brain 84:341-361, 1961
2. Matsuo F, Ajax ET: Palatal myoclonus and denervation supersensitivity in the central nervous system. Ann Neurol 5:72-78,
1979
Auditory Fiber Crossing
C. Keith Whittaker, MD
I applaud Drs Epstein, Stappenbeck, and Karp for presenting their tracings, but I disagree with their interpretation. I think their figure shows that stimulation of the left
ear elicits a wave IV and a wave V-apparently not easily
reproduced (because the three tracings in part B of the
figure are all different), and possibly delayed when compared to the right ear, but still definitely present. Recording between the vertex and the ipsilateral or contralateral
ear clearly shows both a wave IV and a wave V.
Low Blood Levels
of Phenobarbital
Due to Poor
Gastrointestinal Solubility
of Phenobarbital Tablets
Norbert0 Alvarez, MD," Ellen Hartford, RN,*
and Edward Cavalleri, MSt
W e report our experience with a brand of phenobarbital
that resulted in low blood levels in patients with welldocumented compliance. The patients involved were 18
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