Midbrain disorders of vertical gaze: a quantitative re-evaluation

Vertikale Blickparesen bei dorsalem Mittelhirnsyndrom und anderen Erkrankungen

Hintergrund

Die vertikale Blickparese (vBP) ist ein typisches Symptom bei Läsionen des dorsalen Mittelhirns. Die klinische Ausprägung der vBP kann dabei stark variieren und im Rahmen eines dorsalen Mittelhirnsyndroms (DMS) mit zusätzlichen Symptomen wie einer Konvergenzparese, einem Konvergenzretraktionsnystagmus, einer verminderten Pupillenreaktion oder einer Skew Deviation vergesellschaftet sein. Je nach Lokalisation und Größe der Läsion kann auch eine Kombination mit weiteren zentralen Motilitätsstörungen vorliegen.

Material und Methode

Im Rahmen einer retrospektiven Studie wurden die Patientendaten unserer neuroophthalmologischen Ambulanz über einen Zeitraum von 25 Jahren nach Fällen mit Einschränkungen konjugierter vertikaler Augenbewegungen durchsucht und hinsichtlich ihrer neuroorthoptischen Befunde und Ätiologien ausgewertet.

Resultate

Es wurden 202 Patienten mit vBP identifiziert. Das Befundspektrum reichte von einer isolierten Sakkadenstörung nur nach oben bis hin zum kompletten Ausfall aller willkürlichen und reflektorischen vertikalen Augenbewegungen. Nur 12 vBP lagen isoliert vor. Ursächlich war bei 155 Patienten ein DMS, wovon aber nur 18 Fälle dem von Parinaud geprägten Syndrombild (vBP + Konvergenzparese ± Pupillenstörung ohne weitere Symptome) entsprachen; 42 Patienten mit DMS zeigten lediglich eine Sakkadenparese. Der Aufblick war bei DMS insgesamt mehr eingeschränkt als der Abblick. Die häufigsten Begleitsymptome waren eine Konvergenzparese (49 %), Konvergenznystagmus (40 %), Pupillenstörung (32 %), Skew Deviation (21 %) und Blickrichtungsnystagmus (15 %). In 58 Fällen traten weitere zentrale Okulomotorikstörungen auf. Bis zum 18. Lebensjahr war eine vBP bei 58 % der Patienten durch Gehirntumoren bedingt, wohingegen nach dem 60. Lebensjahr neben einem DMS durch Infarkte (41 %) v. a. degenerative Erkrankungen (44 %) ursächlich waren.

Schlussfolgerungen

Langsame und schnelle Augenbewegungen nach oben und unten werden im Hirnstamm unterschiedlich generiert, geleitet und integriert und können daher bei Läsionen des Mittelhirns verschieden stark gestört sein. Die Ergebnisse verdeutlichen zudem die enge Lagebeziehung der Zentren für vertikale Augenbewegungen, Konvergenz und Pupillenreaktion im dorsalen Mittelhirn. Die Kombination einer vBP mit weiteren neuroophthalmologischen Diagnosen kann daher eine topografische und ätiologische Zuordnung erleichtern.

An alternative mechanism of crossed vertical gaze palsy in unilateral mesodiencephalic infarction

Crossed vertical gaze palsy refers to a rare combination of elevation paresis in one eye and depression palsy in the fellow eye. It was once reported in a patient with unilateral infarction involving the mesodiencephalic junction, and was ascribed to selective disruption of the fibers projecting from the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) to the oculomotor nuclear complex. Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a rare cause of ophthalmoplegia and crossed vertical gaze palsy has not been described in this disorder. Our patient with a circumscribed acute infarction involving the left mesodiencephalic junction due to CADASIL showed both upward and downward gaze palsy in both eyes, but more marked depression paresis in the ipsilesional eye and more conspicuous elevation deficit in the contralesional eye, which was consistent with crossed vertical gaze palsy. We provide alternate explanation for this rare phenotype of vertical gaze palsy. Selective disruption of riMLF fibers may cause crossed vertical gaze palsy in unilateral mesodiencephalic lesion.

Ocular Motor Dysfunction Due to Brainstem Disorders

BACKGROUND

The brainstem contains numerous structures including afferent and efferent fibers that are involved in generation and control of eye movements.

EVIDENCE ACQUISITION

These structures give rise to distinct patterns of abnormal eye movements when damaged. Defining these ocular motor abnormalities allows a topographic diagnosis of a lesion within the brainstem.

RESULTS

Although diverse patterns of impaired eye movements may be observed in lesions of the brainstem, medullary lesions primarily cause various patterns of nystagmus and impaired vestibular eye movements without obvious ophthalmoplegia. By contrast, pontine ophthalmoplegia is characterized by abnormal eye movements in the horizontal plane, while midbrain lesions typically show vertical ophthalmoplegia in addition to pupillary and eyelid abnormalities.

CONCLUSIONS

Recognition of the patterns and characteristics of abnormal eye movements observed in brainstem lesions is important in understanding the roles of each neural structure and circuit in ocular motor control as well as in localizing the offending lesion.

Vertical Head Thrusting in Acquired Supranuclear Vertical Ophthalmoplegia

Patients with congenital ocular motor apraxia (OMA) typically show head thrusts while attempting to shift gaze. In congenital OMA, this compensatory head motion mostly occurs in the horizontal plane. Two patients with acquired palsy of voluntary vertical gaze and continuous upward gaze deviation, one from aortic surgery and the other from multiple infarctions involving the mesodiencephalic junction, showed intermittent downward head thrusting to redirect the eyes straight ahead or downward. The head thrusting behavior improved markedly after surgical correction of the upward gaze deviation in one patient. Vertical head thrusting may be a characteristic sign of acquired vertical gaze palsy when combined with vertical gaze deviation.

Ischemic syndromes causing dizziness and vertigo

Dizziness/vertigo and imbalance are the most common symptoms of vertebrobasilar ischemia. Even though dizziness/vertigo usually accompanies other neurologic symptoms and signs in cerebrovascular disorders, a diagnosis of isolated vascular vertigo is increasing markedly by virtue of recent developments in clinical neurotology and neuroimaging. It is important to differentiate isolated vertigo of a vascular cause from more benign disorders involving the inner ear, since therapeutic strategies and prognosis differ between these two conditions. Over the last decade, we have achieved a marked development in the understanding and diagnosis of vascular dizziness/vertigo. Introduction of diffusion-weighted magnetic resonance imaging (MRI) has greatly enhanced detection of infarctions in patients with vascular dizziness/vertigo, especially in the posterior-circulation territories. However, well-organized bedside neurotologic evaluation is even more sensitive than MRI in detecting acute infarction as a cause of spontaneous prolonged vertigo. Furthermore, detailed evaluation of strategic infarctions has elucidated the function of various vestibular structures of the brainstem and cerebellum. In contrast, diagnosis of isolated labyrinthine infarction still remains a challenge. This diagnostic difficulty also applies to isolated transient dizziness/vertigo of vascular origin. Regarding the common nonlacunar mechanisms in the acute vestibular syndrome from small infarctions, individual strategies may be indicated to prevent recurrences of stroke in patients with vascular vertigo.

Bedside evaluation of dizzy patients

In recent decades there has been marked progress in the imaging and laboratory evaluation of dizzy patients. However, detailed history taking and comprehensive bedside neurotological evaluation remain crucial for a diagnosis of dizziness. Bedside neurotological evaluation should include examinations for ocular alignment, spontaneous and gaze-evoked nystagmus, the vestibulo-ocular reflex, saccades, smooth pursuit, and balance. In patients with acute spontaneous vertigo, negative head impulse test, direction-changing nystagmus, and skew deviation mostly indicate central vestibular disorders. In contrast, patients with unilateral peripheral deafferentation invariably have a positive head impulse test and mixed horizontal-torsional nystagmus beating away from the lesion side. Since suppression by visual fixation is the rule in peripheral nystagmus and is frequent even in central nystagmus, removal of visual fixation using Frenzel glasses is required for the proper evaluation of central as well as peripheral nystagmus. Head-shaking, cranial vibration, hyperventilation, pressure to the external auditory canal, and loud sounds may disclose underlying vestibular dysfunction by inducing nystagmus or modulating the spontaneous nystagmus. In patients with positional vertigo, the diagnosis can be made by determining patterns of the nystagmus induced during various positional maneuvers that include straight head hanging, the Dix-Hallpike maneuver, supine head roll, and head turning and bending while sitting. Abnormal smooth pursuit and saccades, and severe imbalance also indicate central pathologies. Physicians should be familiar with bedside neurotological examinations and be aware of the clinical implications of the findings when evaluating dizzy patients.

Bimedial rectus hypermetabolism in convergence spasm as observed on positron emission tomography

A 52-year-old man developed vertical gaze palsy, convergence spasm, and convergence-retraction nystagmus due to glioblastoma of the right thalamus. 18F-fluorodeoxyglucose positron emission tomography (PET) inadvertently demonstrated markedly increased metabolism in the medial rectus muscles. The hypermetabolism indicates active contraction of these extraocular muscles due to excessive convergence drive attributed to inappropriate activation or disrupted inhibition of convergence neurons by the diencephalic lesion.

Neurophysiology and neuroanatomy of smooth pursuit: lesion studies

Smooth pursuit impairment is recognized clinically by the presence of saccadic tracking of a small object and quantified by reduction in pursuit gain, the ratio of smooth eye movement velocity to the velocity of a foveal target. Correlation of the site of brain lesions, identified by imaging or neuropathological examination, with defective smooth pursuit determines brain structures that are necessary for smooth pursuit. Paretic, low gain, pursuit occurs toward the side of lesions at the junction of the parietal, occipital and temporal lobes (area V5), the frontal eye field and their subcortical projections, including the posterior limb of the internal capsule, the midbrain and the basal pontine nuclei. Paresis of ipsiversive pursuit also results from damage to the ventral paraflocculus and caudal vermis of the cerebellum. Paresis of contraversive pursuit is a feature of damage to the lateral medulla. Retinotopic pursuit paresis consists of low gain pursuit in the visual hemifield contralateral to damage to the optic radiation, striate cortex or area V5. Craniotopic paresis of smooth pursuit consists of impaired smooth eye movement generation contralateral to the orbital midposition after acute unilateral frontal or parietal lobe damage. Omnidirectional saccadic pursuit is a most sensitive sign of bilateral or diffuse cerebral, cerebellar or brainstem disease. The anatomical and physiological bases of defective smooth pursuit are discussed here in the context of the effects of lesion in the human brain.

Truncal contrapulsion in pretectal syndrome

Truncal contrapulsion in association with pretectal syndrome has not been described previously. We report a patient with vertical-gaze palsy and severe truncal contrapulsion due to an infarction in the mesodiencephalic junction. Truncal contrapulsion in this patient may have resulted from the disruption of the ascending fibers in the crossed cerebellothalamic tract.

Isolated vertical diplopia as the initial manifestation of presumed pretectal and anterior hypothalamic germinomas

A 21-year-old man with a 5-month history of diplopia caused by isolated vertical ocular misalignment had normal laboratory studies, including brain magnetic resonance imaging (MRI). Eight months after the onset of diplopia, he reported dry mouth, polydipsia, polyuria, and absent sweating. Examination now disclosed light-near dissociation of the pupillary responses, convergence-retraction nystagmus, and upgaze palsy. MRI revealed enhancing suprasellar and pretectal masses presumed to be germinomas. Two years after brain irradiation and systemic chemotherapy, no lesions are apparent on MRI and hypothalamic dysfunction has partially resolved. In a young patient with isolated vertical diplopia and normal brain imaging, one should consider an early pretectal syndrome and inquire after manifestations of hypothalamic dysfunction.

Third Cranial Nerve Palsy From Midbrain Neurocysticercosis: Repeated Exacerbation on Tapering Corticosteroids

Third cranial nerve palsy is rare in neurocysticercosis and is usually caused by supratentorial or sub-arachnoid lesions with accompanying hydrocephalus or meningitis. We report a patient who presented with third cranial nerve palsy caused by neurocysticercosis involving the midbrain. The patient showed repeated exacerbation of symptoms on tapering corticosteroids. The experience with this patient indicates that tapering of corticosteroids should be performed very slowly in such cases.