Patients suffering from Parinaud syndrome show vertical gaze palsy and other neurological deficits triggered by lesions of nerve nuclei located in the dorsal midbrain.
The most common symptom of PS is the inability to look upwards. However, while patients are unable to move their eyes upwards, downward movements are only disturbed in severe cases of PS. Impairment of upward eye movement can result in a permanent downward gaze.
Patients suspicious for PS should undergo neurologic examinations to identify the precise location of neuronal damage. In this context, passive eye movements may be completely preserved, i.e., it should be possible to provoke full vertical eye movements by rotating the patient's head while they are focusing on an immobile object (doll’s eye maneuver). This test proves that gaze palsy is indeed caused by functional impairment of brain structures superior to motor neurons; the latter are working fine.
If patients try to force upward eye movements, they often provoke a pathologic nystagmus that results from simultaneous, uncontrolled contraction of several ocular muscles. Eyes converge in an attempt to look upwards, retract and repeat this operation. This kind of nystagmus can most easily be stimulated with an optokinetic drum turned downwards.
Horizontal eye movements are not commonly affected in PS. However, it has been described that lateral eye movements occur slower than medial eye movements. Therefore, there may be an incongruence between both eyes during horizontal movements.
Furthermore, patients show pupillary anomalies corresponding to pseudo-Argyll Robertson effects. Pupils are widened and do not contract upon stimulation with light, but they do narrow to focus on a near object. Accommodation reflexes may be altered. Such symptoms may be more pronounced after attempts to look upwards.
Additionally, PS patients may maintain their eyelids abnormally retracted.
In summary, leading symptoms for PS are:
An ophthalmologic examination may reveal a swollen head of the optic nerve.
Of note, additional symptoms may be present if further cerebral structures are affected by tumors, increased intracranial pressure, infection, inflammation or any other underlying disease. Eye movements not typically seen in PS may be disturbed due to oculomotor nerve palsy, trochlear nerve palsy or abducens nerve palsy, for example.
Clinical and ophthalmologic examination allow for diagnosis of PS. In order to establish a therapeutic scheme, the underlying disease needs to be identified. Age, gender and a possible medical history of demyelinating diseases such as multiple sclerosis may give important hints as to the most likely cause of PS in this specific case.
Diagnostic imaging, particularly magnetic resonance imaging and computed tomography scans, are applied to identify space-occupying masses in the pineal gland and the midbrain. These same techniques allow for an evaluation of the ventricular system. Findings may point at an increased intracranial pressure due to hydrocephalus. Disseminated foci of inflammation and reactive gliosis, also visible in magnetic resonance imaging, are characteristic of multiple sclerosis. Older patients should undergo the aforementioned scans immediately since they may have sustained cerebral infarction and the time window for stroke treatment is very narrow.
Treatment largely depends on the underlying disease. If it is curable, neurologic deficits affecting eye movements should resolve within a few months time. Only in non-curable cases, e.g., when a patient suffers from developmental defects that cannot be treated, surgical interventions can be considered. Vertical gaze palsy in PS is caused by paresis of the superior rectus muscle and that, in turn, means that the inferior rectus muscle is missing its antagonist. Thus, the recession of the latter may help to correct a constant downward gaze. This same procedure is usually applied to correct convergence-retraction nystagmus.
Prognosis largely depends on the underlying disease. If it can be treated, neurologic deficits usually diminish over the course of several months. In the case of increased intracranial pressure due to hydrocephalus, abrupt relief may be associated with rapid resolution of neurological symptoms.
Any disease that may damage the superior colliculus of the tectum, the posterior commissure, and the rostral interstitial nucleus of medial longitudinal fasciculus, which are the main parts of the cerebrum that affect vertical eye movement, may possibly cause PS.
Older studies almost exclusively name tumors of the pineal gland as triggers of PS      . These space-occupying masses presumably compress the posterior commissure and as they are rarely located in the median plane, they generally cause unilateral symptoms. Of note, intrinsic tumors of the midbrain or neoplasms of any other adjacent tissue may lead to similar neurologic deficits. Depending on the precise location of such neoplasias, other symptoms may, however, dominate the clinical picture. Because in the ventral direction, the posterior commissure is delimited by the third ventricle, increasing pressures due to hydrocephalus may also damage this structure and cause PS.
Cerebral ischemia, infection, and inflammation affecting any of the aforementioned anatomical structures are other possible causes of PS. With regards to infectious diseases, brain stem toxoplasmosis, for instance, may trigger this disease.
In some cases, degenerative alterations that may occur in the course of multiple sclerosis, other demyelinating disorders or progressive supranuclear palsy may account for the neurological deficits observed in PS patients. Metabolic disorders such as congenital Niemann-Pick disease and Wilson's disease as well as acquired kernicterus may cause PS. This condition has also been related to barbiturate abuse . Rarely, hemorrhages and developmental defects manifesting as vascular malformations have been reported as triggers of PS.
PS patients most commonly belong to one of three major risk groups.
On the one hand, there are those patients that suffer from neoplasms affecting their pineal gland or midbrain. With regards to the pineal gland, germinomas are most frequently detected, but astrocytoma and pineocytoma may also develop. These space-occupying masses compress cerebral structures in close proximity that are involved in eye movement. The corresponding patients are usually adolescents, sometimes prepubertal children.
On the other hand, there are young women previously diagnosed with multiple sclerosis. Here, demyelination damages neuronal structures and impairs their function.
Finally, PS is often diagnosed in older patients that recently suffered a cerebral infarction.
The most common symptoms of PS are vertical gaze palsy, blunt pupillary reflexes as well as nystagmus, but other ocular and neurologic symptoms may be present   . To comprehend the pathophysiology of this disease, the neuroanatomical basis for the above-mentioned movements and reflexes needs to be understood.
The medial longitudinal fasciculus comprises axons of cranial nerves III, IV and V (oculomotor nerve, trochlear nerve, and abducens nerve, respectively). These nerves are essential for a wide variety of eye movements, e.g., for vertical gaze control and many fibers cross the posterior commissure. The medial longitudinal fasciculus ascends to the interstitial nuclei of Cajal in the midbrain and the oculomotor nuclei   . Here, signals are transduced to the cortex. Vertical gaze palsy may thus result from lesions to the medial longitudinal fasciculus, the posterior commissure or the midbrain itself.
The neuronal chain that controls the pupillary reflex consists of retinal neurons, pretectal nuclei, the Erdinger-Westphal nuclei in the rostral midbrain and finally the ciliary ganglions from which the iris sphincter muscle is innervated. Both the pretectal nuclei as well as the Erdinger-Westphal nuclei may directly be affected in PS. The Erdinger-Westphal nuclei are also involved in the accommodation reflex and therefore, a blunt pupillary reflex may be observed.
As can be seen, eye movements largely depend on midbrain structures, adjacent nuclei as well as on axons that ascend to and descend from these nuclei. It has been stated that lesions of the medial longitudinal fasciculus and the posterior commissure most frequently account for PS .
No preventive measures can be recommended.
Parinaud syndrome (PS) is named in honor of Henri Parinaud, a French ophthalmologist, and neurologist who practiced in the second half of the 19th century. His two areas of expertise combine perfectly to understand this disease, which is characterized by the patient's inability to perform certain eye movements, most notably to control their gaze in the vertical direction  . These are neurological deficits that manifest because of damage to the dorsal midbrain, which is why PS is also designated dorsal midbrain syndrome.
Eye movements are principally controlled by the superior colliculus of the tectum, which is located in the dorsal part of the midbrain. In patients suffering from PS, this and possibly adjacent structures, e.g, the pretectal area, the posterior commissure and the rostral interstitial nucleus of medial longitudinal fasciculus, are compromised by any underlying disease. In this context, a neoplasm in close proximity that compresses the midbrain, ischemia due to cerebral infarction or infectious and inflammatory processes may trigger PS. Tumors of the pineal gland or midbrain structures are the most common causes of PS.
Because the above-mentioned structures are not only involved in vertical gaze control, PS patients typically show additional symptoms. Their pupillary reflex is disturbed and a pathological nystagmus, as well as unilateral or bilateral eyelid retraction, may be present.
The medical term Parinaud syndrome (PS) refers to an eye disease comprising the inability to gaze upwards, a blunted pupillary reflex and nystagmus, i.e., uncontrolled, rhythmic eye movement. The disease is also called dorsal midbrain syndrome because damage to neuronal structures located in this part of the brain account for the aforementioned symptoms.
Any disease compromising neuronal structures involved in eye movement control may trigger PS. Most frequently, tumors of the midbrain itself or of the pineal gland, a hormonal gland in close proximity to the midbrain, cause PS by compressing the neighboring tissue. Such tumors are often diagnosed in young people. A second, also very common cause of PS is an increased intracranial pressure, a hydrocephalus. This condition will affect other cerebral structures as well. The latter also applies to degenerative diseases like multiple sclerosis, infection, and inflammation of brain structures. Older people showing signs of PS may have sustained a stroke.
PS patients are unable to look upwards, but usually, don't have any problems to gaze downwards. If they strain to look up, contraction of lower eye muscles may lead to the aforementioned nystagmus. The pupils of PS patients are often widened and don't contract upon light exposure. They do, however, narrow to focus on near objects.
More generalized conditions may trigger additional symptoms.
Diagnosis of PS is based on clinical and ophthalmological examination. However, further diagnostic measures have to be applied to identify the cause of PS. Most commonly, imaging techniques such as magnetic resonance imaging and computed tomography scans are applied to this end. They may help to identify tumors, obstructed cerebral ventricle and tissue inflammation.
The underlying disease needs to be treated. If this is possible, neurologic deficits usually resolve over the course of time. In some severe cases with a persistent downward gaze, surgery may be considered.