Answer: An oculogyric crisis is a form of dystonia that results in involuntary upwards deviation of the eyes.
The movement of the eyeball is controlled by the actions of six different muscles, each one responsible for moving the eyeball in a different direction. Collectively, they are called the extraocular muscles. Normally, these muscles work in concert with each other to move the eyeballs in the intended direction.
During an oculogyric crisis, the normal tone of these muscles change, resulting in an unusual deviation of the eye. Usually, both eyes can look upwards intentionally, but during an oculogyric crisis, it is possible for just one eye to move independently of the other. Sometimes, this is also called a functional tonic eye deviation.
The duration of an oculogyric crisis may vary. Sometimes, they may last for just seconds at a time. In severe circumstances, they can persist for hours. (Chapter 30 - Functional eye movement disorders)
Many times, an oculogyric crisis does not occur in isolation of other atypical motor movement. Other dyskinetic observations include oral dystonia, such as tongue protrusions or lip smacking. Sometimes, a person also has blepharospasms, the random and atypical opening and closing of the eyelids. There are unusual limb movements as well, such as choreoathetosis, which is when the digits on the hands or toes rapidly flex, open or close, with no apparent rhythmicity or purpose.
Cause of oculogyric crisis
Oculogyric crises were first described by doctors who studied patients with encephalitis lethargica, or post-encephalitic Parkinsonism, a brain disease occurring in the years following World War I. Even though encephalitis lethargica is very rare today, oculogyric crises can be observed after a patient has been exposed to certain drugs. For example, some antipsychotics, which affect dopamine signaling in the midbrain, may lead to an acute dystonic response. First generation antipsychotics may produce these symptoms since they directly modulate dopamine signaling, but oculogyric crises have also been reported after treatment with second and third generation neuroleptics, such as aripiprazole and olanzapine. It is estimated that about 2% of patients taking neuroleptics may experience oculogyric crisis, especially in young men.
Some serotonergic compounds may also induce the symptom. It is likely that excessive serotonin signaling in circuits of the brain could lead to the oculogyric crisis. For example, the drug fluvoxamine, which is a selective serotonin reuptake inhibitor (SSRI), may induce the upwards gaze (Fluvoxamine induced oculogyric dystonia and manic switch in a patient with obsessive compulsive disorder)
Epilepsy may also be a cause. In epilepsy, a person's cortical activity becomes dysregulated. As a result, there may be motor command signals that trigger oculomotor nerve activity unpredictably, which can result in the upward turn of the eye.
Several other conditions are known to cause an oculogyric crisis, most commonly alongside various movement disorders. Parkinson's disease, Fahr disease, neurosyphilis, Rett syndrome, multiple sclerosis, and acute trauma can all induce oculogyric crisis.
Mechanism of oculogyric crisis
The exact underlying neurological changes that lead to the observed symptoms are still unknown. One major theory suggests that the higher order movement areas such as the striatum or subthalamic nucleus are responsible for controlling the oculomotor centers of the brain. These areas may get injured or damaged in some way, especially among patients with post-encephalitic Parkinsonism.
A second explanation for the unusual eye movement behavior is related to the vestobulo-ocular reflex, one of the fastest reflex arcs in the entire body. In the normal case, the vestibulo-ocular reflex (VOR) is a gaze stabilizing response. When a person's head is turned side to side, as in the Halmagyi-Curthroys Impulse test, the center of vision remains facing forward for a short delay, even after the head is forcibly moved. If this reflex arc is disrupted in some way, it may result in the eye turning upwards.
Treatment of oculogyric crisis
Generally, the treatment for the symptom is to remove the drugs that were associated with the onset of the dystonia. An oculogyric crisis is usually not life-threatening, but it is indicative that some neural circuitry is changed in a way that leads to the incorrect muscle tone.