Operculum syndrome: unusual feature of herpes simplex encephalitis.

Herpes simplex encephalitis in adults and young patients carries a high mortality and morbidity. Its presentation may be nonspecific, sometimes hampering early diagnosis. Two young children are reported with herpes simplex encephalitis in whom the operculum syndrome was an outstanding feature. This syndrome is caused by focal, bilateral cortical damage to the anterior opercular regions resulting in anarthria and impairment of mastication and swallowing. After initiation of treatment with acyclovir in the early stage of the disease, the outcomes in both patients were characterized by good general recovery with persistence of deficits of speech, mastication, and swallowing, more pronounced in the patient who was comatose during the illness. Early recognition of the operculum syndrome as a presenting feature of herpes simplex encephalitis may expedite the diagnosis and thereby improve the prognosis.

Binaural interaction in the brain-stem auditory evoked potential: evidence for a delay line coincidence detection mechanism.

The binaural interaction component (BIC) of the brain-stem auditory evoked potential (BAEP) was studied in 13 normally hearing adults by subtracting the response to binaural clicks from the algebraic sum of monaural responses. Eight or 16 electrodes on the head and neck were referred to a non-cephalic site, the binaural stimuli were delivered either simultaneously or with an inter-aural time difference (delta t) of 0.2-1.6 msec, and masking noise was presented to the non-stimulated ear. With simultaneous binaural clicks a BIC was identifiable in every subject, the most consistent peaks being a scalp-positive potential (P1) peaking approximately 0.2 msec after wave V and a scalp negativity (N1) 0.7 msec later. Similar potentials were identifiable in 6/7 subjects with delta t of 0.4 msec, 5/7 at 0.8 msec but only 1/7 at 1.2 msec. This suggests that the BIC may be associated with sound localization mechanisms which are sensitive to a similar range of delta t. On increasing delta t from 0.0 to 0.8 msec, the BIC was progressively delayed by approximately half the inter-aural time difference, with no suggestion of increasing temporal dispersion. This supports the notion of a 'delay line coincidence detection' mechanism in which the BIC represents the output of binaurally responsive neurones, probably in the superior olivary complex, which are 'tuned' to a particular delta t by the relative lengths of presynaptic axons relaying input from either ear. The distribution of the BIC in sagittal and coronal electrode chains was compared with that of binaural BAEP components I-VI and found to bear the closest resemblance to wave IV. It is suggested that both components may originate largely in the lateral lemnisci.

Sound lateralization, brainstem auditory evoked potentials and magnetic resonance imaging in multiple sclerosis.

Two tests of binaural hearing, namely intensity discrimination of alternating monaural clicks and interaural time difference (IATD) discrimination of binaural clicks, were performed in 28 patients with definite multiple sclerosis (MS) and 12 with an isolated brainstem lesion compatible with demyelination. Intensity discrimination defects were found in 53.5% and IATD defects in 82% of definite MS cases, although no overt auditory symptoms were reported and pure tone audiology was unremarkable. Corresponding figures in the isolated lesion group were 25% and 33%. Defects were manifested either by an abnormal 'bias' in favour of one ear or by a broadened 'spread' of responses (i.e., greater range of uncertainty). Brainstem auditory evoked potentials (BAEPs) were abnormal in 75% of the definite MS cases but only in 8% of the isolated lesion group. BAEP abnormalities involving component III on one or both sides were invariably associated with a defect of IATD discrimination. This is consistent with disruption of input to the superior olivary complex, the most peripheral structure where binaurally responsive units are sensitive to IATD. Lesions causing abnormality of component V alone less frequently resulted in impaired IATD discrimination, possibly because at rostral levels the IATD is encoded by the location rather than the timing of neuronal activity. In magnetic resonance imaging (MRI), abnormalities of the medulla, pons or midbrain were demonstrated in all MS patients tested and 45% of those with isolated brainstem lesions. The correlation with BAEP abnormalities was plausible in some patients but apparently anomalous in others. More severe BAEP abnormalities than would have been expected on the basis of MRI may have been due to small unresolved lesions, while the more frequent finding of normal or mildly abnormal BAEPs in conjunction with extensive MRI abnormalities may have been due to the fact that areas of abnormal signal reflect an increase in the water content of the tissue rather than demyelination per se.

Magnetic resonance imaging of the optic nerve in optic neuritis.

Magnetic resonance imaging (MRI) of the optic nerves using the STIR (short inversion time inversion recovery) sequence was performed in 37 adult patients with a recent or past attack of optic neuritis. MRI revealed high-signal regions in 84% of symptomatic and 20% of asymptomatic nerves. The mean longitudinal extent of lesions was 1 cm. Slow or poor visual recovery was associated with more extensive lesions, or lesions within the optic canal. Disk swelling was usually associated with anterior lesions but also occurred with lesions in the canal. Visual evoked potentials were even more sensitive than MRI in detecting lesions and are still the investigation of choice in suspected demyelinating disease involving the optic nerve.

Visual function and pattern visual evoked response in optic neuritis.

The disparity between clinical visual function and pattern visual evoked response (VER) was studied in 53 patients who had suffered an attack of optic neuritis (ON) more than six months before. The visual functions tested included Snellen visual acuity, colour vision, visual field, and contrast sensitivity. The effect of pattern presentation, check size, and luminance was tested by recording VERs with several stimulus configurations. VER amplitudes were found to be associated with the outcome of all four clinical tests, independently of check size, luminance, or the presentation method used. On the other hand VER latencies were hardly ever related to the results of any of the four clinical visual tests. These findings support the idea that VER amplitude provides information about visual spatial perception, while VER latency is more related to the extent of demyelination.

Estimation of visual function after optic neuritis: a comparison of clinical tests.

A group of 53 patients who had suffered an attack of unilateral (n = 45) or bilateral (n = 8) optic neuritis more than six months before were subjected to a battery of tests to determine their spatial contrast sensitivity, visual field, and colour vision. The 106 eyes investigated were classified according to their clinical status and visual acuity at the time of the study into unaffected (n = 45), recovered (n = 33), and non-recovered (n = 28). At least one of the three tests gave an abnormal result in 67%, 88%, 100% of the three groups respectively. The results obtained with these three tests showed a significant statistical association.