Parinaud Syndrome - Causes, Pathophysiology, Clinical Manifestations, Evaluation, and Treatment

Introduction

Henri Parinaud, a French ophthalmologist, initially described Parinaud syndrome in the late 1800s. Parinaud described it in several case reviews of patients who had problems with related eye movements and gaze paralysis. He determined that a quadrigeminal region (a complicated area in the back of the midbrain that houses critical neuronal, artery, and venous structures) lesion was the root of this issue. Upgaze palsy (bilateral limitation of eye movements in upward gaze) and convergence paralysis (unable to focus the visual axis on a closer or farther away object) were included in Henri Parinaud's original description. The three symptoms of upgaze paralysis, convergence retraction nystagmus (particularly when trying an upward glance, both eyeballs regularly converge and retreat into the orbit), and pupillary light-near dissociation (the near-sighted reaction (accommodative response), is unaffected while the pupillary light responsiveness is diminished) have recently been included in the definition of Parinaud syndrome. Along with downgaze palsy, it can also occasionally feature conjugate downgaze in the primary position. Other names for this syndrome are:

• The Sylvian aqueduct syndrome.

• Dorsal midbrain syndrome.

• Pretectal syndrome.

• Koerber-Salus-Elschnig Syndrome.

What Are the Causes of Parinaud Syndrome?

The conditions that can lead to Parinaud syndrome are:

• Pineal gland tumors.

• Midbrain infarctions (loss of blood supply or bleeding in the midbrain).

• Multiple sclerosis (autoimmune disease affecting the brain and the spinal cord).

• Midbrain hemorrhage (brainstem vascular lesion).

• Encephalitis (brain inflammation).

• Arteriovenous malformations (an abnormal connection between the arteries and veins).

• Infections (toxoplasmosis).

• Trauma.

• Obstructive hydrocephalus (increased pressure within the skull due to cerebrospinal fluid flow blockage).

• Tonic-clonic seizures (a type of epilepsy).

This condition has been mentioned in reports after brachytherapy (a procedure to treat cancers) instillation. However, pineal gland tumors and other midbrain diseases such as hemorrhage and infarction, are the most frequent causes. It is also discovered that the fundamental etiology of Parinaud syndrome changes with age. The young population is more susceptible to neoplastic reasons than middle-aged and older people, who are more likely to develop vascular causes.

What Is the Pathophysiology of Parinaud Syndrome?

The superior colliculus (midbrain structure) is where the rostral (towards the front-end) midbrain and pretectum (midbrain structure consisting of nuclei) are compressed, which results in the constellation of signs and symptoms known as Parinaud syndrome.

The interstitial nucleus of Cajal (INC) and the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF), which control upgaze, are damaged in upgaze palsy. Vertical saccades (a swift, simultaneous change in the focus of both eyes between two or more phases in the same direction) are predominantly controlled by the riMLF, but the INC is in charge of all other vertical eye movements, such as vertical gaze-holding and skew deviation (acquired vertical misalignment of the eyes). Both of these nuclei decussate in the posterior commissure and are located near the cerebral aqueduct (structure present in the brainstem). They are particularly vulnerable to unilateral space-occupying lesions and increased cerebrospinal fluid pressures because of their location in the posterior commissure. Due to its bilateral innervation, downgaze is often only affected by significant space-occupying lesions or bilateral lesions in PS until late in the disease.

• Convergence Retraction Nystagmus: According to a theory, injury to the midbrain supranuclear fibers causes convergence retraction nystagmus. Normally, these fibers have an inhibitory effect on the third nerve nucleus, which prevents the extraocular muscles that are innervated by cranial nerve three from contracting. Due to the superior and inferior rectus muscles' continual stimulation as a result of the absence of their inhibitory function, the globe retracts. In addition, when the medial rectus is stimulated, the lateral rectus is overpowered, resulting in involuntary convergence.

• Light-Near Dissociation: Damage to the pretectal and Edinger-Westphal nuclei, or to the pretectal nucleus' decussating fibers in the posterior commissure, causes light-near dissociation. The inability to constrict the pupil and loss of parasympathetic innervation to the iris sphincter muscles are consequences of damage to these nuclei. It is believed that the nuclei in charge of the pupillary light reflex are located more dorsally than the nuclei in charge of the near reflex, rendering them more vulnerable to the effects of compression. Therefore, pupillary light reflex loss and near reflex preservation are the typical outcomes of dorsal midbrain injuries.

• Bilateral Lid Retraction: Similar to convergence retraction nystagmus, bilateral lid retraction (Collier sign) is hypothesized to be caused by a lack of supranuclear input to the third nerve nucleus. The levator palpebrae superioris receives continual stimulation through the oculomotor nerve without the inhibitory impact of the supranuclear fibers, resulting in lid retraction.

What Are the Clinical Manifestations of Parinaud Syndrome?

Parinaud syndrome symptoms include:

• Upward gaze paralysis, particularly conjugate upgaze palsy. There may occasionally be a combination of upgaze and downgaze palsy, and in rare cases, simply downgaze palsy. Traditionally, the vestibulo-ocular reflex is unaffected.

• The best way to induce convergence retraction nystagmus is with an optokinetic nystagmus drum (a test to induce the optokinetic nystagmus) that is traveling downward. An attempt to look up causes the eyes to jerk episodically.

• Light near-dissociation, or loss of pupillary light responses.

• Less than 25 percent of patients experience convergence loss.

• About 40 percent of patients have upper eyelid retraction (Collier's "tucked lid" sign).

• The "setting sun" sign, a conjugate downgaze, could be present in the primary position.

How Is Parinaud Syndrome Evaluated?

In all cases, a comprehensive neurological evaluation is recommended. It is recommended to perform the following:

• A fundoscopy (an examination to check the fundus of the eye).

• Visual acuity testing (eye examination that evaluates the capacity to distinguish fine characteristics of a letter or symbol at a particular distance).

• Visual field testing (the ability to see out of the corners of the eye is measured with a visual field test).

• Color vision testing (checks the ability to differentiate between the colors).

• Pupillary testing (used to assess the brain stem function).

Due to the vast range of potential explanations for this illness, a comprehensive workup that includes neuroimaging is necessary to identify the underlying cause. Other possible examinations are:

• Thyroid function testing.

• Serum protein electrophoresis (the types of proteins in a blood sample's fluid (serum) component are measured by this laboratory test).

• Infection screening.

• Cerebrospinal fluid analyses.

• Blood acetylcholine receptor antibodies.

• Nerve conduction tests.

How Is Parinaud Syndrome Treated?

Symptoms in patients with early hydrocephalus may entirely disappear. Therefore, the prime objective is to address the underlying cause quickly before irreversible harm develops. Surgery can be used to treat upgaze palsies that are persistent. The surgical alternatives include superior transposition (altering the mechanical properties of the muscle action) of the medial and lateral rectus muscles (eye muscles), superior rectus excision, and inferior rectus recession. All of these techniques lessen the severity of retraction nystagmus by reducing upgaze and aberrant head position. Other methods include visual training and tracking activities, which can also be employed with patients who have persistent gaze palsies.

Conclusion

The ocular (eye) symptoms of Parinaud's syndrome typically improve gradually over months, especially when the underlying cause is treated; sustained improvement beyond the first three to six months following onset is rare. However, with the insertion of a ventriculoperitoneal shunt (a cerebral shunt used to drain excess cerebrospinal fluid), fast remission has been documented following the normalization of intracranial pressure. Everyone should get yearly eye exams to identify and address any current vision issues, both basic and complex. However, if it seems that one could be suffering from Parinaud syndrome, people should get medical attention as soon as possible.