MRI of the eye muscles in a case of ophthalmoplegia caused by common carotid artery occlusion suggests ischemic myopathy.

Ocular muscle palsies following carotid artery disease is thought to be caused by ischemia of the cranial oculomotor nerves but it may also be due to ischemia of the extraocular muscles (EOM). We studied a patient with common carotid artery occlusion syndrome (CCAOS) to elucidate the two competing hypotheses. MRI and sonography of the orbita showed oedematous swelling of all left EOM. MRI short-tau inversion recovery (STIR) sequences showed hyperintensities and a prolonged T2-relaxation time in EOM indicating muscle oedema. It decreased within two weeks as ophthalmoplegia improved. For several reasons ischemic EOM myopathy rather than ischemic neuropathy seems to be the morphological correlate of ophthalmoplegia after ipsilateral CCAOS in this patient.

Structural brain changes following peripheral vestibulo-cochlear lesion may indicate multisensory compensation.

BACKGROUND: Do central mechanisms account for the variability of clinical recovery following peripheral vestibulo-cochlear lesions? OBJECTIVE: To investigate structural (morphological) plasticity in the human brain following unilateral vestibulo-cochlear lesions which might contribute to central vestibular compensation. METHODS: The authors compared regional grey matter volume (GMV) changes in patients after surgical removal of unilateral acoustic neuroma with age-matched control subjects, and hypothesised morphometric changes in the vestibular and auditory cortices which may be related to functional disability scores. Patients were examined with a battery of neuro-otological tests and clinical scores to assess vestibular and auditory disability. RESULTS: Voxel-based morphometry was used for categorical comparison between patients and age- and gender-matched controls. GMV increase was found bilaterally in primary somatosensory cortices and motion-sensitive areas in the medial temporal gyrus (MT). Simple regression analysis revealed a GMV increase (1) in the contralesional superior temporal gyrus/posterior insula to be correlated with decreasing clinically assessed vestibular deficits; (2) in the contralesional inferior parietal lobe with decreasing functional impairment of daily living activities; and (3) in the contralesional auditory cortex (Heschl gyrus) with decreasing hearing impairment. CONCLUSIONS: These data may suggest structural cortical plasticity in multisensory vestibular cortex areas of patients with unilateral peripheral vestibulo-cochlear lesion after surgical removal of acoustic neuroma. As changes of GMV were related to vestibular function, structural brain changes may reflect central mechanisms of vestibular compensation.

Distinct basal ganglia hyperechogenicity in idiopathic basal ganglia calcification.

We report a 67-year-old patient with idiopathic basal ganglia calcification (IBGC). He presented with progressive cognitive impairment, frontal lobe dysfunction, mild leg spasticity, and levodopa (L-dopa)-responsive parkinsonism. Transcranial sonography (TCS) revealed marked hyperechogenicity of the basal ganglia and periventricular spaces bilaterally. The detected signal alterations showed a fairly symmetric distribution and corresponded to the hyperintense calcifications depicted on the computer tomography brain scan. The combination of symmetric hyperechogenic areas adjacent to the lateral ventricles and of the basal ganglia may serve as an imaging marker characteristic of IBGC. Hyperechogenicity due to extended basal ganglia calcification as presented here is distinct from the pattern of hyperechogenicity caused by heavy metal accumulation, which is described to be less striking. In addition to atypical parkinsonian syndromes such as progressive supranuclear palsy and multiple system atrophy, IBGC is thus another differential diagnosis of parkinsonism with basal ganglia hyperechogenicity.

Structural changes in the human brain following vestibular neuritis indicate central vestibular compensation.

Vestibular neuritis (VN) is a sudden unilateral vestibular failure (UVF) with a variable course. Caloric hyporesponsiveness often persists, and it is largely unknown why patients with the same degree of hyporesponsiveness show different functional recovery. As the peripheral vestibular deficit alone does not seem to determine functional recovery, it was the aim of this study to elucidate whether structural (morphological) brain changes (1) contribute to central vestibular compensation, and (2) account for the variability of clinical recovery in VN. Structural global gray-matter volume (GMV) changes in 15 VN patients were compared with age-matched controls. Morphometric changes in multisensory vestibular cortices, which may be related to functional disability scores, were hypothesized. Patients were examined with neuro-otological tests and clinical scores to assess vestibular disability. Using voxel-based morphometry (VBM, SPM2), categorical comparison revealed GMV increase in patients' multisensory vestibular cortices [insula, inferior parietal lobe (IPL), superior temporal gyrus (STG)], cerebellum, and motion-sensitive areas in the middle temporal area (MT). GMV decrease was found in the midline pontomedullary junction. Simple regression analysis revealed (1) GMV increase in insula and retroinsular vestibular cortex and STG with improving clinically assessed vestibular deficits, and (2) GMV increase in insula vestibular cortex and STG with improving self-assessed vestibular impairment. For the first time, these data suggest structural cortical plasticity in multisensory vestibular-cortex areas in VN that are related to clinical vestibular function and vertigo. As increase of GMV was related to an improvement of vestibular function, structural alterations may be related to central vestibular compensation.

Visual search disorders in acute and chronic homonymous hemianopia: lesion effects and adaptive strategies.

Patients with homonymous hemianopia due to occipital brain lesions show disorders of visual search. In everyday life this leads to difficulties in reading and spatial orientation. It is a matter of debate whether these disorders are due to the brain lesion or rather reflect compensatory eye movement strategies developing over time. For the first time, eye movements of acute hemianopic patients (n= 9) were recorded during the first days following stroke while they performed an exploratory visual-search task. Compared to age-matched control subjects their search duration was prolonged due to increased fixations and refixations, that is, repeated scanning of previously searched locations. Saccadic amplitudes were smaller in patients. Right hemianopic patients were more impaired than left hemianopic patients. The number of fixations and refixations did not differ significantly between both hemifields in the patients. Follow-up of one patient revealed changes of visual search over 18 months. By using more structured scanpaths with fewer saccades his search duration decreased. Furthermore, he developed a more efficient eye-movement strategy by making larger but less frequent saccades toward his blind side. In summary, visual-search behavior of acute hemianopic patients differs from healthy control subjects and from chronic hemianopic patients. We conclude that abnormal visual search in acute hemianopic patients is related to the brain lesion. We provide some evidence for adaptive eye-movement strategies developed over time. These adaptive strategies make the visual search more efficient and may help to compensate for the persisting visual-field loss.

Why do patients with impaired vergence not show "saccadic" vergence?

Low gain of the smooth-pursuit system causes correcting saccades that are clinically observed as "saccadic pursuit." In contrast, low gain of the vergence system during tracking does not appear to cause "saccadic tracking." To further evaluate whether this clinical observation is caused by a missing interaction of vergence to step and ramp targets, vergence eye movements to step-ramp, step, and ramp targets in 3-dimensional space were tested. Results show that vergence to a step and a ramp stimulus is additive in the step-ramp paradigm, indicating no interaction of both components.

Visual search disorders beyond pure sensory failure in patients with acute homonymous visual field defects.

Patients with homonymous visual field defects (HVFD) are often crucially disabled during self-guided visual exploration of their natural environment. Abnormal visual search may be related to the sensory deficit, deficient spatial orientation or compensatory eye movements. We tested the hypothesis that visual search in HVFD is purely determined by the visual-sensory deficit by comparing nine patients with HVFD due to occipital stroke in an acute stage to nine healthy subjects with technically simulated "virtual" homonymous visual field defects (vHVFD) and to nine controls with normal visual fields. The simulated gaze-contingent visual field defects in vHVFD subjects were individually matched to the patients' HVFD with respect to their size and side. Eye movements were recorded while subjects searched for targets among distractors and indicated target detection by clicks. All patients, in particular those with lesions involving the inferior occipito-temporal (fusiform) gyrus, but also those with small lesions restricted to the visual cortex, showed longer search durations than vHVFD subjects. This was tightly related to the higher number of fixations and particularly "re-fixations" (repeated scanning of fixated items). Working memory across saccades during the search was intact (no increased "re-clicks"). Scanpath strategies were similar in patients and vHVFD subjects. For both groups amplitude and frequency of saccades did not differ between the hemifields. In HVFD patients with acute occipital brain lesions, visual input failure does not fully account for abnormal visual search. It might either result from disconnections of the primary visual cortex to associated occipital and temporal brain areas or reflect an early stage of compensatory eye movements which differ from chronic HVFD patients.

Age-related changes of vergence under natural viewing conditions.

Vergence eye movements were recorded with the scleral search-coil system in 32 healthy subjects (ages 19-73 years) to characterize the age-related effects on the dynamic parameters of vergence responses to step (transient components) and ramp or sinusoidal targets (sustained components) under natural viewing conditions. Transient vergence showed an age-related increase in latency and decreases in peak velocity and acceleration in the binocular stimulus condition but not in accommodative vergence. Sustained vergence showed no age-related effect in the binocular condition, but there was an age-related decrease in accommodative vergence steady-state velocity and an increase in latency. Age-related changes of the transient and sustained components were very similar to those reported for saccades and smooth pursuit; they thus might support a distinction between a sustained and transient vergence system. Furthermore, such age-related effects have to be taken into account when assessing eye movement disorders in neurodegenerative and cerebrovascular diseases.

Effect of 3,4-diaminopyridine on the postural control in patients with downbeat nystagmus.

Downbeat nystagmus (DBN) is a common, usually persistent ocular motor sign in vestibulocerebellar midline lesions. Postural imbalance in DBN may increase on lateral gaze when downbeat nystagmus increases. 3,4-Diaminopyridine (3,4-DAP) has been shown to suppress the slow-phase velocity component of downbeat nystagmus and its gravity-dependent component with concomitant improvement of oscillopsia. Because the pharmacological effect is thought to be caused by improvement of the vestibulocerebellar Purkinje cell activity, the effect of 3,4-DAP on the postural control of patients with downbeat nystagmus syndrome was examined. Eye movements were recorded with the video-based Eyelink II system. Postural sway and pathway were assessed by posturography in lateral gaze in the light and on eye closure. Two out of four patients showed an improvement of the area of postural sway by 57% of control (baseline) on eye closure. In contrast, downbeat nystagmus in gaze straight ahead and on lateral gaze did not benefit in these two patients, implying a specific influence of 3,4-DAP on the vestibulocerebellar control of posture. It was concluded that 3,4-DAP may particularly influence the postural performance in patients with downbeat nystagmus.

Palsy of "fast" and "slow" vergence by pontine lesions.

The role of pontine nuclei in vergence eye movements to "step" targets ("fast" vergence) is unknown. Eye movements were recorded in two patients with unilateral pontine infarctions and in 11 healthy controls. In addition to the deficit of "slow" vergence, "fast" vergence was particularly impaired. However, conjugate saccades did not differ from controls, but smooth pursuit eye movements did. The authors conclude that "fast" vergence palsy is not only caused by midbrain but also upper pontine lesions.