Pathophysiology of slow vertical saccades in progressive supranuclear palsy

OBJECTIVES

To investigate the relative roles of burst neurons (which generate the saccadic command) and omnipause neurons (which gate the activity of burst neurons) in the pathogenesis of slow saccades in progressive supranuclear palsy (PSP).

BACKGROUND

Experimental inactivation of mesencephalic burst neurons impairs vertical but not horizontal saccades. Experimental inactivation of omnipause neurons causes slowing of both horizontal and vertical saccades. Combining saccadic with vergence movements in healthy subjects induces small, high-frequency, conjugate oscillations, which indicate that omnipause neurons are inhibited.

METHODS

The authors studied seven patients with PSP, six patients with other parkinsonian syndromes, and seven age-matched control subjects. They compared vertical saccades of similar sizes made with or without associated vergence movements. They compared the speed of vertical and horizontal saccades.

RESULTS

Five patients with PSP and the six patients with other parkinsonian made vertical saccades in combination with horizontal vergence; all showed conjugate horizontal oscillations (29 to 41 Hz) during 27% to 93% of saccade-vergence trials. Vertical saccades made in conjunction with vergence movements were not speeded up or increased in size compared with saccades made between equidistant targets for the PSP or parkinsonian groups. Vertical saccades were slowed more than horizontal saccades in the PSP group (p < 0.005) but not in the parkinsonian group.

CONCLUSIONS

Dysfunction of omnipause neurons ("gate dysfunction") is unlikely to be the primary cause of slow vertical saccades in progressive supranuclear palsy. Deficient generation of the motor command by midbrain burst neurons is the more likely cause.

Vertical nystagmus in normal subjects: effects of head position, nicotine and scopolamine

We measured gaze stability in darkness of four normal humans using the search coil technique. Subjects were tested first with their heads erect, and then with their heads positioned 180 degrees upside-down. In each position, subjects held their head stationary for one minute, and then actively performed pitch rotations for 20 sec. All subjects showed sustained chin-beating nystagmus in the upside-down position. Each subject showed a significant increase of slow-phase velocity directed towards their brow after 40 sec in the inverted versus erect position. Pitch head rotation had little effect on subsequent nystagmus, except for transient reversal in one subject. The sustained changes of vertical eye drifts induced by 180 deg change of head position suggest that otolithic factors may contribute to vertical nystagmus in normals. The subjects were retested after wearing a nicotine patch for 2 hours. In three subjects, nicotine induced brow-beating nystagmus; adopting a head-hanging position increased this nystagmus in two subjects. In a third session, subjects were tested after wearing a scopolamine patch for 2 hours; results were generally similar to the control condition. We conclude that normal subjects may show chin-beating ("downbeating") nystagmus in a head-hanging position in darkness, reflecting a normal, physiological change in otolithic inputs brought about by the head orientation.

Ocular oscillations induced by shifts of the direction and depth of visual fixation

Shifts of the point of fixation between two targets aligned on one eye that are located near and far (Müller paradigm) stimulates a combined saccadic-vergence movement. In normal subjects, this test paradigm often induces saccadic oscillations of about 0.3 degrees at 20 to 30 Hz. We measured eye movements using the magnetic search coil technique in 2 patients recovering from viral opsoclonus-myoclonus syndrome, comparing saccadic-vergence responses to the Müller paradigm with conjugate saccades between distant targets. Both patients exhibited intermittent conjugate ocular oscillations of about 4 to 5 degrees amplitude at about 10 Hz. Combined saccadic-vergence movements induced these oscillations twice as often as did conjugate saccades. One patient also exhibited disjunctive ocular oscillations at 10 Hz while sustaining fixation on the near target. The Müller paradigm provides a useful clinical and experimental technique for inducing saccadic oscillations. The probable mechanism is that pontine omnipause neurons, which normally gate saccades, are inhibited during the sustained vergence movement that follows the saccadic component of the response to the Müller paradigm.

Vertical nystagmus in normal subjects: Effects of head position, nicotine and scopolamine

We measured gaze stability in darkness of four normal humans using the search coil technique. Subjects were tested first with their heads erect, and then with their heads positioned 180 degrees upside-down. In each position, subjects held their head stationary for one minute, and then actively performed pitch rotations for 20 sec. All subjects showed sustained chin-beating nystagmus in the upside-down position. Each subject showed a significant increase of slow-phase velocity directed towards their brow after 40 sec in the inverted versus erect position. Pitch head rotation had little effect on subsequent nystagmus, except for transient reversal in one subject. The sustained changes of vertical eye drifts induced by 180 deg change of head position suggest that otolithic factors may contribute to vertical nystagmus in normals. The subjects were retested after wearing a nicotine patch for 2 hours. In three subjects, nicotine induced brow-beating nystagmus; adopting a head-hanging position increased this nystagmus in two subjects. In a third session, subjects were tested after wearing a scopolamine patch for 2 hours; results were generally similar to the control condition. We conclude that normal subjects may show chin-beating (“downbeating”) nystagmus in a head-hanging position in darkness, reflecting a normal, physiological change in otolithic inputs brought about by the head orientation.

A hypothetical scheme for the brainstem control of vertical gaze

OBJECTIVES

To develop a hypothetical scheme to account for clinical disorders of vertical gaze based on recent insights gained from experimental studies.

METHODS

The authors critically reviewed reports of anatomy, physiology, and effects of pharmacologic inactivation of midbrain nuclei.

RESULTS

Vertical saccades are generated by burst neurons lying in the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF). Each burst neuron projects to motoneurons in a manner such that the eyes are tightly coordinated (yoked) during vertical saccades. Saccadic innervation from riMLF is unilateral to depressor muscles but bilateral to elevator muscles, with axons crossing within the oculomotor nucleus. Thus, riMLF lesions cause conjugate saccadic palsies that are usually either complete or selectively downward. Each riMLF contains burst neurons for both up and down saccades, but only for ipsilateral torsional saccades. Therefore, unilateral riMLF lesions can be detected at the bedside if torsional quick phases are absent during ipsidirectional head rotations in roll. The interstitial nucleus of Cajal (INC) is important for holding the eye in eccentric gaze after a vertical saccade and coordinating eye-head movements in roll. Bilateral INC lesions limit the range of vertical gaze. The posterior commissure (PC) is the route by which INC projects to ocular motoneurons. Inactivation of PC causes vertical gaze-evoked nystagmus, but destructive lesions cause a more profound defect of vertical gaze, probably due to involvement of the nucleus of the PC. Vestibular signals originating from each of the vertical labyrinthine canals ascend to the midbrain through several distinct pathways; normal vestibular function is best tested by rotating the patient's head in the planes of these canals.

CONCLUSIONS

Predictions of a current scheme to account for vertical gaze palsy can be tested at the bedside with systematic examination of each functional class of eye movements.

Cancer-related thromboembolic disease in patients with solid tumours: a retrospective analysis

BACKGROUND

Cancer patients frequently suffer thromboembolic events. This study assessed the incidence and resource implications of cancer-related thromboembolic disease (CTD) in a single, large cancer centre.

PATIENTS AND METHODS

A retrospective analysis of patients admitted with CTD and/or the complications of treatment of CTD over a two-year period has been conducted. Forty-eight patients (23 male, 25 female, median age 60 years) with a variety of solid tumours were identified.

RESULTS

The initial presentations were venous thromboses (28 patients) and pulmonary embolism (20 patients). The median interval from cancer diagnosis to the initial episode of CTD was eight (range 0-112) months. Twenty-two patients suffered additional thromboses, despite maintenance warfarin anticoagulation in 18 patients. Six patients experienced anticoagulation-induced haemorrhage. Forty-one (85.4%) patients have died. The median survival from the first thromboembolic event was 8.5 months. The median inpatient stay for management of the first event was 10 (range 4-75) days, accounting for 729 inpatient days during the study period. Recurrent episodes of CTD or complications of anticoagulation resulted in 28 readmissions, accounting for 295 inpatient days. During the two-year period 1024 inpatient days were directly caused by CTD and its complications, representing 6.1% bed occupancy on our unit.

CONCLUSION

This study demonstrates that CTD represents a significant cause of morbidity in cancer patients with considerable resource implications for cancer centres. Improvements in prevention and management of CTD would reduce morbidity and lead to considerable cost savings.