Difference between revisions of "Oculopalatal Tremor"

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|Reviewer=Claudia.Prospero.Ponce
 
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|Date reviewed=June 19, 2020
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|Date reviewed=January 03, 2021
 
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|Meta description=Oculopalatal Tremor
 
|Meta description=Oculopalatal Tremor
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'''I. Introduction'''
 
'''I. Introduction'''
 
   
 
   
Oculopalatal tremor
+
Oculopalatal tremor (OPT) (also known as oculopalatal myoclonus or pharyngo-laryngo-diaphragmatic myoclonus) is an acquired syndrome of continuous and rhythmical movements of
(OPT) (also known as oculopalatal myoclonus or pharyngo-laryngo-diaphragmatic
+
the soft palate combined with pendular nystagmus.  It occurs after injury to the brainstem or cerebellar regions. The concurrent nystagmus can be synchronous or asynchronous, and it may be seen as a convergent or pendular vertical nystagmus, or as a combination of both. When the palatal movements are seen in isolation, without an ocular component, this is simply known as palatal myoclonus.<sup>[1][2]</sup> The most common precipitating cause of OPT is a cerebrovascular accident of the posterior circulation disrupting the dentato-rubro-thalamic tract.  
myoclonus) is an acquired syndrome of continuous and rhythmical movements of
 
the soft palate combined with pendular nystagmus.  It occurs after injury to the brainstem or
 
cerebellar regions. The concurrent nystagmus can be synchronous or asynchronous,
 
and it may be seen as a convergent or pendular vertical nystagmus, or as a
 
combination of both. When the palatal movements are seen in isolation, without
 
an ocular component, this is simply known as palatal myoclonus.<sup>[1][2]</sup> The most common precipitating cause of OPT is a cerebrovascular
 
accident of the posterior circulation disrupting the dentato-rubro-thalamic
 
tract.  
 
  
 
'''II. Pathogenesis'''
 
'''II. Pathogenesis'''
 
   
 
   
OPT is a delayed
+
OPT is a delayed complication of a brainstem lesion affecting the dentato-rubro-thalamic tract, also known as the Guillain-Mollaret triangle (see diagram below). The tract
complication of a brainstem lesion affecting the dentato-rubro-thalamic tract,
+
originates in the cerebellar dentate nucleus and travels to the contralateral red nucleus in the central tegmentum of the midbrain. The tract continues to the ipsilateral inferior olivary nucleus via the central tegmental tract. Damage to or disruption of any part of this tract results in secondary inferior olivary nucleus hypertrophy (IONH), forming the pacemaker of the aberrant signaling that results in OPT. Damage to the dentate nucleus results in contralateral IONH, while damage to the central tegmental tract results in ipsilateral IONH. Although IONH does not necessarily result in the occurrence of OPT, the presence of OPT always requires IONH. It should be noted that hypertrophy is a misnomer, as this phenomenon is due to pseudohypertrophy.
also known as the Guillain-Mollaret triangle (see diagram below). The tract
+
Although both neurons and astrocytes initially enlarge, over time the neurons become vacuolated, eventually atrophying and dying after several years.<sup>[1][2][3][4]</sup> OPT can occur as early as 3 weeks and as late as 49 months after the initial insult but typically occurs within 6 to 8 months. [[File:Triangle-of-guillain-and-mollaret (1).jpg|thumb|A schematic diagram of the dentate-rubro-olivary triangle (or Triangle of Guillain and Mollaret) over a coronal MRI of the brain. The dentate nucleus (blue circle) in the cerebellum sends signals along the superior cerebellar peduncle to the contralateral red nucleus (red circle) in the midbrain, which subsequently sends signals along the central tegmental tract to the inferior olivary nucleus (green circle) in the medulla. (Case courtesy of Dr Maxime St-Amant, <nowiki>https://radiopaedia.org. From the case https://radiopaedia.org/cases/34774</nowiki>). ]]  
originates in the cerebellar dentate nucleus and travels to the contralateral
 
red nucleus in the central tegmentum of the midbrain. The tract continues to
 
the ipsilateral inferior olivary nucleus via the central tegmental tract.
 
Damage to or disruption of any part of this tract results in secondary inferior
 
olivary nucleus hypertrophy (IONH), forming the pacemaker of the aberrant
 
signaling that results in OPT. Damage to the dentate nucleus results in
 
contralateral IONH, while damage to the central tegmental tract results in
 
ipsilateral IONH. Although IONH does not necessarily result in the occurrence
 
of OPT, the presence of OPT always requires IONH. It should be noted that
 
hypertrophy is a misnomer, as this phenomenon is due to pseudohypertrophy.
 
Although both neurons and astrocytes initially enlarge, over time the neurons
 
become vacuolated, eventually atrophying and dying after several years.<sup>[1][2][3][4]</sup> OPT can occur as early as 3 weeks and as late as 49 months
 
after the initial insult but typically occurs within 6 to 8 months.  
 
[[File:Triangle-of-guillain-and-mollaret (1).jpg|thumb|A schematic diagram of the dentate-rubro-olivary triangle (or Triangle of Guillain and Mollaret) over a coronal MRI of the brain. The dentate nucleus (blue circle) in the cerebellum sends signals along the superior cerebellar peduncle to the contralateral red nucleus (red circle) in the midbrain, which subsequently sends signals along the central tegmental tract to the inferior olivary nucleus (green circle) in the medulla. (Case courtesy of Dr Maxime St-Amant, <nowiki>https://radiopaedia.org. From the case https://radiopaedia.org/cases/34774</nowiki>). ]]  
 
  
On a cellular level,
+
On a cellular level, the presence of abnormal soma-somatic gap junctions and electronic coupling among inferior olive neurons is responsible for the origination of the oscillator signal. This phenomenon occurs secondary to the inciting insult and resulting cellular pseudohypertrophy of the inferior olive(s), producing irregular and abrupt signals from the inferior olivary neurons, unlike the smooth rhythmic movement of the vertical nystagmus seen in OPT. Eventually, modification of the signal leaving the injured inferior olivary neurons via their climbing
the presence of abnormal soma-somatic gap junctions and electronic coupling
+
fibers at the level of the cerebellum results in the smooth, rhythmic output seen in pendular nystagmus (view this link to compare other forms of nystagmus).<sup>[5][6]</sup>  
among inferior olive neurons is responsible for the origination of the
 
oscillator signal. This phenomenon occurs secondary to the inciting insult and
 
resulting cellular pseudohypertrophy of the inferior olive(s). This results in
 
irregular and abrupt signals from the inferior olivary neurons, unlike the
 
smooth rhythmic movement of the vertical nystagmus seen in OPT. Eventually, modification
 
of the signal leaving the injured inferior olivary neurons via their climbing
 
fibers at the level of the cerebellum results in the smooth, rhythmic output
 
seen in pendular nystagmus (view this
 
link to compare other forms of nystagmus).<sup>[5][6]</sup>  
 
  
It is postulated that
+
It is postulated that 2 types of OPT exist: 1) Lateral form and 2) Midline form.  
2 types of OPT exist: a lateral form and a midline form. The lateral form is
+
1) The lateral form is thought to occur as unilateral or asymmetric palatal tremor with unequal vertical nystagmus but conjugate torsional oscillation.
thought to occur as unilateral or asymmetric palatal tremor with unequal
+
2) The midline form is thought to manifest as a combination of symmetrical palatal tremor and symmetrical vertical nystagmus.  
vertical nystagmus but conjugate torsional oscillation and to be associated
+
 
with unilateral IONH. The midline form is thought to manifest as a combination
+
It was initially thought that the lateral form is associated with unilateral IONH and the midline form with bilateral IONH; however, later studies have been equivocal
of symmetrical palatal tremor and symmetrical vertical nystagmus. It was
+
and not demonstrated sufficient correlation of laterality with clinical phenotype.<sup>[3][4]</sup>  
initially thought that the lateral form is associated with unilateral IONH and
 
the midline form with bilateral IONH; however, later studies have been equivocal
 
and not demonstrated sufficient correlation of laterality with clinical
 
phenotype.<sup>[3][4]</sup>  
 
  
 
'''III. Epidemiology'''
 
'''III. Epidemiology'''
  
The frequency of OPT
+
The frequency of OPT even among brainstem stroke patients is very low, and little data exists regarding its true incidence. A retrospective review by Jang et al of 82 patients with OPT found that the average age of diagnosis was 54 years with a male tendency. The most common underlying etiology was a vascular lesion in the brain stem, accounting for 80% of cases.<sup>[7]</sup> Other potential causes include demyelination, infection, or other CNS inflammation and iatrogenic damage to the brainstem or cerebellum.
even among brainstem stroke patients is very low, and little data exists
 
regarding its true incidence. A retrospective review by Jang et al of 82
 
patients with OPT found that the average age of diagnosis was 54 years with a
 
male tendency. The most common underlying etiology was a vascular lesion in the
 
brain stem, accounting for 80% of cases.<sup>[7]</sup> Other potential causes include demyelination, infection,
 
or other CNS inflammation and iatrogenic damage to the brainstem or cerebellum.
 
  
 
'''IV. Diagnosis'''
 
'''IV. Diagnosis'''
  
The rhythmic movements
+
The rhythmic movements of the pharynx are most appropriately described as a tremor and are caused by regular contraction of the levator veli palatini muscle. Ocular oscillations are most commonly found to be synchronous with the palatal tremor, although asynchronous cases do occur. The oscillations typically occur at 1-3 Hz. The diagnosis of OPT requires the identification of both abnormal palatal movements and nystagmus. Occasionally ear clicks are reported, due to tremors of the tensor veli palatini. Although the palate is most often affected, movements of the eyes, facial muscles, pharynx, tongue, larynx, diaphragm, mouth of the Eustachian tube, and, rarely, of the neck, trunk, and extremities may also occur. Interestingly, the nystagmus sometimes disappears with sleep, but the palatal movements usually persist.   
of the pharynx are most appropriately described as a tremor and are caused by
 
regular contraction of the levator veli palatini muscle. Ocular oscillations
 
are most commonly found to be synchronous with the palatal tremor, although
 
asynchronous cases do occur. The oscillations typically occur at 1-3 Hz. The
 
diagnosis of OPT requires the identification of both abnormal palatal movements
 
and nystagmus. Occasionally ear clicks are reported, due to tremors of the
 
tensor veli palatini. Although the palate is most often affected, movements of
 
the eyes, facial muscles, pharynx, tongue, larynx, diaphragm, mouth of the
 
Eustachian tube, and, rarely, of the neck, trunk, and extremities may also
 
occur. Interestingly, the nystagmus sometimes disappears with sleep, but the
 
palatal movements usually persist.   
 
  
 
For video examples of this entity see the links below:
 
For video examples of this entity see the links below:
 
 
 
1- [https://www.youtube.com/watch?v=OqZk5eeaL-U this video] for an example of oculopalatal tremor.   
 
1- [https://www.youtube.com/watch?v=OqZk5eeaL-U this video] for an example of oculopalatal tremor.   
 
 
2- [https://n.neurology.org/content/91/22/e2104#DC1] <ref>Teaching Video NeuroImages: Oculopalatal myoclonus A possible consequence of brainstem injury Omolara Lawal, Adeniyi Fisayo. Neurology Nov 2018, 91 (22) e2104-e2105; DOI: 10.1212/WNL.0000000000006563</ref>
 
2- [https://n.neurology.org/content/91/22/e2104#DC1] <ref>Teaching Video NeuroImages: Oculopalatal myoclonus A possible consequence of brainstem injury Omolara Lawal, Adeniyi Fisayo. Neurology Nov 2018, 91 (22) e2104-e2105; DOI: 10.1212/WNL.0000000000006563</ref>
  
The main structural
+
The main structural abnormality of OPT is hypertrophy of the inferior olive in the upper medulla. Olivary enlargement can often be seen on magnetic resonance imaging (MRI)
abnormality of OPT is hypertrophy of the inferior olive in the upper medulla.
+
several months following the initial brainstem insult as unilateral or bilateral T2 hyperintense signal of one or both inferior olivary nuclei. In many cases, MRI or computed tomography scan will identify the nature of the initial underlying lesion and will show IONH (the pimento sign).<sup>[2] [10]  </sup>
Olivary enlargement can often be seen on magnetic resonance imaging (MRI)
 
several months following the initial brainstem insult as unilateral or
 
bilateral T2 hyperintense signal of one or both inferior olivary nuclei. In
 
many cases, MRI or computed tomography scan will identify the nature of the
 
initial underlying lesion and will show IONH (the pimento sign).<sup>[2] [10]  </sup>
 
  
Histologically, the
+
Histologically, the olivary nucleus has enlarged, vacuolated neurons with enlarged astrocytes.
olivary nucleus has enlarged, vacuolated neurons with enlarged astrocytes.
 
  
 
'''V. Differential Diagnosis'''
 
'''V. Differential Diagnosis'''
  
OPT falls within the
+
OPT falls within the larger category of myorhythmias, which are a range of disorders characterized by slow (1-4 Hz),  repetitive, rhythmic movements occurring at rest. They include:
larger category of myorhythmias, which are a range of disorders characterized
+
- palatal myoclonus
by slow (1-4 Hz),  repetitive, rhythmic
+
- oculo-masticatory myorhythmia
movements occurring at rest. They include palatal myoclonus, oculo-masticatory
+
- limb myorhythmias
myorhythmia, limb myorhythmias, and Holmes tremor. Myorhythmias must be
+
- Holmes tremor.  
differentiated from myoclonic movement disorders that originate secondary to
+
 
cortical, spinal, or peripheral lesions and are characterized by erratic,
+
Myorhythmias must be differentiated from myoclonic movement disorders that originate secondary to cortical, spinal, or peripheral lesions and are characterized by erratic, faster (>7Hz), and often purposeful movements.
faster (>7Hz), and often purposeful movements.
 
  
•Oculo-masticatory
+
•Oculo-masticatory myorhythmia is another form of myorhythmia, with ocular nystagmus (convergent-divergent or vertical) accompanied by rhythmic contractions of the facial and masticatory muscles. It has a similar pathogenesis within the brainstem, though it causes less IONH. It is often a secondary feature noted in Whipple’s disease, and its presence should raise concern for this diagnosis.
myorhythmia is another form of myorhythmia, with ocular nystagmus
 
(convergent-divergent or vertical) accompanied by rhythmic contractions of the
 
facial and masticatory muscles. It has a similar pathogenesis within the
 
brainstem, though it causes less IONH. It is often a secondary feature noted in
 
Whipple’s disease, and its presence should raise concern for this diagnosis.
 
  
•Oculo-facio-skeletal
+
•Oculo-facio-skeletal myorhythmia is like oculo-masticatory myorhythmia, but with limb involvement.
myorhythmia is like oculo-masticatory myorhythmia, but with limb involvement.
 
  
•Disorders of the
+
•Disorders of the myelin sheaths, most commonly multiple sclerosis, of the central nervous system can cause acquired pendular nystagmus. A slightly faster, but still regular oscillation of 3-5 Hz is seen, and it is not associated orofacial movements. Lesions are most commonly seen in the paramedian tracts.
myelin sheaths, most commonly multiple sclerosis, of the central nervous system
 
can cause acquired pendular nystagmus. A slightly faster, but still regular
 
oscillation of 3-5 Hz is seen, and it is not associated orofacial movements.
 
Lesions are most commonly seen in the paramedian tracts.
 
  
•Epilepsia partialis
+
•Epilepsia partialis continua is a form of focal epilepsy. Slow, rhythmic tremors similar to myorhythmias are seen in isolated parts of the body. Differentiation from OPT and similar disorders can be made via electromyography (shorter burst durations) as well as electroencephalography (jerk-locked charges).
continua is a form of focal epilepsy. Slow, rhythmic tremors similar to
 
myorhythmias are seen in isolated parts of the body. Differentiation from OPT
 
and similar disorders can be made via electromyography (shorter burst
 
durations) as well as electroencephalography (jerk-locked charges).
 
  
•Cortical tremors are
+
•Cortical tremors are irregular with a higher frequency of oscillation. They are typically genetically inherited and are often associated with epilepsy.<sup>[1]</sup>
irregular with a higher frequency of oscillation. They are typically
 
genetically inherited and are often associated with epilepsy.<sup>[1]</sup>
 
  
 
'''VI. Treatment'''
 
'''VI. Treatment'''
Line 149: Line 71:
 
''Medical''
 
''Medical''
  
Oculopalatal tremor is
+
Oculopalatal tremor is a disorder that is difficult to treat and has shown varied responses to different types of drugs. There has been moderate success in the treatment of acquired pendular nystagmus with the use of gabapentin and memantine, but these medications have not been proven effective for the palatal tremor. The proposed mechanism of action is through blockade of N-methyl-D-aspartate (NMDA) receptors at the level of the inferior olivary nucleus, reducing synchronized firing. Trials of anticholinergics, such as trihexyphenidyl and scopolamine, have also shown moderate effectiveness; however, these drugs can cloud consciousness as well as cause drowsiness and other anti-cholinergic side effects, limiting their therapeutic efficacy. Lastly, retrobulbar botulinum toxin administration has been shown to offer temporary reprieve in certain situations; however, there are the risks of retrobulbar hemorrhage and varying degrees of external ophthalmoplegia and ptosis.<sup>[8][9]</sup>
a disorder that is difficult to treat and has shown varied responses to
 
different types of drugs. There has been moderate success in the treatment of
 
acquired pendular nystagmus with the use of gabapentin and memantine, but these
 
medications have not been proven effective for the palatal tremor. The proposed
 
mechanism of action is through blockade of N-methyl-D-aspartate (NMDA)
 
receptors at the level of the inferior olivary nucleus, reducing synchronized
 
firing. Trials of anticholinergics, such as trihexyphenidyl and scopolamine,
 
have also shown moderate effectiveness; however, these drugs can cloud
 
consciousness as well as cause drowsiness and other anti-cholinergic side
 
effects, limiting their therapeutic efficacy. Lastly, retrobulbar botulinum
 
toxin administration has been shown to offer temporary reprieve in certain
 
situations; however, there are the risks of retrobulbar hemorrhage and varying
 
degrees of external ophthalmoplegia and ptosis.<sup>[8][9]</sup>
 
  
 
''Surgical''
 
''Surgical''
  
There is no definitive
+
There is no definitive surgical intervention that has been reliably efficacious. There has been limited success with rectus muscle tenotomy or disinsertion to reduce the amplitude of nystagmus<sup>[2][9]</sup>; however, due to the rarity of OPT, there have been no surgical treatment trials undertaken to investigate efficacy of this treatment or other forms of acquired nystagmus
surgical intervention that has been reliably efficacious. There has been
 
limited success with rectus muscle tenotomy or disinsertion to reduce the
 
amplitude of nystagmus<sup>[2][9]</sup>; however, due to the rarity of OPT, there have been no surgical
 
treatment trials undertaken to investigate efficacy of this treatment or other
 
forms of acquired nystagmus
 
  
 
'''VII. Prognosis & Outcome'''
 
'''VII. Prognosis & Outcome'''
  
Despite the
+
Despite the availability of the aforementioned treatment options, OPT is usually intractable as it is often refractory to both medical and surgical interventions and spontaneous remission is uncommon. It can be a severely debilitating disease due to persistent oscillopsia, significantly handicapping individuals who suffer from it due to lifelong limitation of mobility and function.<sup>[2]</sup>
availability of the aforementioned treatment options, OPT is usually
 
intractable as it is often refractory to both medical and surgical
 
interventions and spontaneous remission is uncommon. It can be a severely
 
debilitating disease due to persistent oscillopsia, significantly handicapping
 
individuals who suffer from it due to lifelong limitation of mobility and
 
function.<sup>[2]</sup>
 
  
 
'''IV. References'''
 
'''IV. References'''

Latest revision as of 22:23, January 3, 2021


I. Introduction

Oculopalatal tremor (OPT) (also known as oculopalatal myoclonus or pharyngo-laryngo-diaphragmatic myoclonus) is an acquired syndrome of continuous and rhythmical movements of the soft palate combined with pendular nystagmus.  It occurs after injury to the brainstem or cerebellar regions. The concurrent nystagmus can be synchronous or asynchronous, and it may be seen as a convergent or pendular vertical nystagmus, or as a combination of both. When the palatal movements are seen in isolation, without an ocular component, this is simply known as palatal myoclonus.[1][2] The most common precipitating cause of OPT is a cerebrovascular accident of the posterior circulation disrupting the dentato-rubro-thalamic tract.

II. Pathogenesis

OPT is a delayed complication of a brainstem lesion affecting the dentato-rubro-thalamic tract, also known as the Guillain-Mollaret triangle (see diagram below). The tract originates in the cerebellar dentate nucleus and travels to the contralateral red nucleus in the central tegmentum of the midbrain. The tract continues to the ipsilateral inferior olivary nucleus via the central tegmental tract. Damage to or disruption of any part of this tract results in secondary inferior olivary nucleus hypertrophy (IONH), forming the pacemaker of the aberrant signaling that results in OPT. Damage to the dentate nucleus results in contralateral IONH, while damage to the central tegmental tract results in ipsilateral IONH. Although IONH does not necessarily result in the occurrence of OPT, the presence of OPT always requires IONH. It should be noted that hypertrophy is a misnomer, as this phenomenon is due to pseudohypertrophy.

Although both neurons and astrocytes initially enlarge, over time the neurons become vacuolated, eventually atrophying and dying after several years.[1][2][3][4] OPT can occur as early as 3 weeks and as late as 49 months after the initial insult but typically occurs within 6 to 8 months.

A schematic diagram of the dentate-rubro-olivary triangle (or Triangle of Guillain and Mollaret) over a coronal MRI of the brain. The dentate nucleus (blue circle) in the cerebellum sends signals along the superior cerebellar peduncle to the contralateral red nucleus (red circle) in the midbrain, which subsequently sends signals along the central tegmental tract to the inferior olivary nucleus (green circle) in the medulla. (Case courtesy of Dr Maxime St-Amant, https://radiopaedia.org. From the case https://radiopaedia.org/cases/34774). 

On a cellular level, the presence of abnormal soma-somatic gap junctions and electronic coupling among inferior olive neurons is responsible for the origination of the oscillator signal. This phenomenon occurs secondary to the inciting insult and resulting cellular pseudohypertrophy of the inferior olive(s), producing irregular and abrupt signals from the inferior olivary neurons, unlike the smooth rhythmic movement of the vertical nystagmus seen in OPT. Eventually, modification of the signal leaving the injured inferior olivary neurons via their climbing fibers at the level of the cerebellum results in the smooth, rhythmic output seen in pendular nystagmus (view this link to compare other forms of nystagmus).[5][6]

It is postulated that 2 types of OPT exist: 1) Lateral form and 2) Midline form. 1) The lateral form is thought to occur as unilateral or asymmetric palatal tremor with unequal vertical nystagmus but conjugate torsional oscillation. 2) The midline form is thought to manifest as a combination of symmetrical palatal tremor and symmetrical vertical nystagmus.

It was initially thought that the lateral form is associated with unilateral IONH and the midline form with bilateral IONH; however, later studies have been equivocal and not demonstrated sufficient correlation of laterality with clinical phenotype.[3][4]

III. Epidemiology

The frequency of OPT even among brainstem stroke patients is very low, and little data exists regarding its true incidence. A retrospective review by Jang et al of 82 patients with OPT found that the average age of diagnosis was 54 years with a male tendency. The most common underlying etiology was a vascular lesion in the brain stem, accounting for 80% of cases.[7] Other potential causes include demyelination, infection, or other CNS inflammation and iatrogenic damage to the brainstem or cerebellum.

IV. Diagnosis

The rhythmic movements of the pharynx are most appropriately described as a tremor and are caused by regular contraction of the levator veli palatini muscle. Ocular oscillations are most commonly found to be synchronous with the palatal tremor, although asynchronous cases do occur. The oscillations typically occur at 1-3 Hz. The diagnosis of OPT requires the identification of both abnormal palatal movements and nystagmus. Occasionally ear clicks are reported, due to tremors of the tensor veli palatini. Although the palate is most often affected, movements of the eyes, facial muscles, pharynx, tongue, larynx, diaphragm, mouth of the Eustachian tube, and, rarely, of the neck, trunk, and extremities may also occur. Interestingly, the nystagmus sometimes disappears with sleep, but the palatal movements usually persist.

For video examples of this entity see the links below: 1- this video for an example of oculopalatal tremor. 2- [1] [1]

The main structural abnormality of OPT is hypertrophy of the inferior olive in the upper medulla. Olivary enlargement can often be seen on magnetic resonance imaging (MRI) several months following the initial brainstem insult as unilateral or bilateral T2 hyperintense signal of one or both inferior olivary nuclei. In many cases, MRI or computed tomography scan will identify the nature of the initial underlying lesion and will show IONH (the pimento sign).[2] [10]  

Histologically, the olivary nucleus has enlarged, vacuolated neurons with enlarged astrocytes.

V. Differential Diagnosis

OPT falls within the larger category of myorhythmias, which are a range of disorders characterized by slow (1-4 Hz),  repetitive, rhythmic movements occurring at rest. They include: - palatal myoclonus - oculo-masticatory myorhythmia - limb myorhythmias - Holmes tremor.

Myorhythmias must be differentiated from myoclonic movement disorders that originate secondary to cortical, spinal, or peripheral lesions and are characterized by erratic, faster (>7Hz), and often purposeful movements.

•Oculo-masticatory myorhythmia is another form of myorhythmia, with ocular nystagmus (convergent-divergent or vertical) accompanied by rhythmic contractions of the facial and masticatory muscles. It has a similar pathogenesis within the brainstem, though it causes less IONH. It is often a secondary feature noted in Whipple’s disease, and its presence should raise concern for this diagnosis.

•Oculo-facio-skeletal myorhythmia is like oculo-masticatory myorhythmia, but with limb involvement.

•Disorders of the myelin sheaths, most commonly multiple sclerosis, of the central nervous system can cause acquired pendular nystagmus. A slightly faster, but still regular oscillation of 3-5 Hz is seen, and it is not associated orofacial movements. Lesions are most commonly seen in the paramedian tracts.

•Epilepsia partialis continua is a form of focal epilepsy. Slow, rhythmic tremors similar to myorhythmias are seen in isolated parts of the body. Differentiation from OPT and similar disorders can be made via electromyography (shorter burst durations) as well as electroencephalography (jerk-locked charges).

•Cortical tremors are irregular with a higher frequency of oscillation. They are typically genetically inherited and are often associated with epilepsy.[1]

VI. Treatment

Medical

Oculopalatal tremor is a disorder that is difficult to treat and has shown varied responses to different types of drugs. There has been moderate success in the treatment of acquired pendular nystagmus with the use of gabapentin and memantine, but these medications have not been proven effective for the palatal tremor. The proposed mechanism of action is through blockade of N-methyl-D-aspartate (NMDA) receptors at the level of the inferior olivary nucleus, reducing synchronized firing. Trials of anticholinergics, such as trihexyphenidyl and scopolamine, have also shown moderate effectiveness; however, these drugs can cloud consciousness as well as cause drowsiness and other anti-cholinergic side effects, limiting their therapeutic efficacy. Lastly, retrobulbar botulinum toxin administration has been shown to offer temporary reprieve in certain situations; however, there are the risks of retrobulbar hemorrhage and varying degrees of external ophthalmoplegia and ptosis.[8][9]

Surgical

There is no definitive surgical intervention that has been reliably efficacious. There has been limited success with rectus muscle tenotomy or disinsertion to reduce the amplitude of nystagmus[2][9]; however, due to the rarity of OPT, there have been no surgical treatment trials undertaken to investigate efficacy of this treatment or other forms of acquired nystagmus

VII. Prognosis & Outcome

Despite the availability of the aforementioned treatment options, OPT is usually intractable as it is often refractory to both medical and surgical interventions and spontaneous remission is uncommon. It can be a severely debilitating disease due to persistent oscillopsia, significantly handicapping individuals who suffer from it due to lifelong limitation of mobility and function.[2]

IV. References

1.     ↑ Jump up to:1.0 1.1 1.2 Baizabal-Carvallo JF, Cardoso F, Jankovic J. Myorhythmia: phenomenology, etiology, and treatment. Mov Disord. 2015;30(2):171-179. 

2.     ↑ Jump up to:2.0 2.1 2.2 2.3 2.4 Talks SJ, Elston JS. Oculopalatal myoclonus: eye movement studies, MRI findings and the difficulty of treatment. Eye. 1997;11(1):19-24. 

3.     ↑ Jump up to:3.0 3.1 Nakada T, Kwee IL. Oculopalatal myoclonus. Brain. 1986;109(3):431-441. 

4.     ↑ Jump up to:4.0 4.1 Kim JS, Moon SY, Choi KD, Kim JH, Sharpe JA. Patterns of ocular oscillation in oculopalatal tremor. Neurology. 2007;68(14):1128-1135. 

5.     Jump up↑ Borruat, FX. Oculopalatal tremor: current concepts and new observations. Curr Opin Neurol. 2013;26(1):67-73. 

6.     Jump up↑ Shaikh AG, Hong S, Liao K, et al.  Oculopalatal tremor explained by a model of inferior olivary hypertrophy and cerebellar plasticity. Brain 2010;133(1):923-940. 

7.     Jump up↑ Jang L, Borruat FX. Oculopalatal tremor: variations on a theme by Guillain and Mollaret. Eur Neurol. 2014;72(3-4):144-149. 

8.     Jump up↑ Strupp M, Thurtell MJ, Shaikh AG, Brandt T, Zee DS, Leigh RJ. Pharmacotherapy of vestibular and ocular motor disorders, including nystagmus. J Neurol. 2011;258(7):1207-1222.

9.     ↑ Jump up to:9.0 9.1 Thurtell MJ, Leigh RJ. Therapy for nystagmus. J Neuroophthalmol. 2010;30(4):361-371.

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  1. Teaching Video NeuroImages: Oculopalatal myoclonus A possible consequence of brainstem injury Omolara Lawal, Adeniyi Fisayo. Neurology Nov 2018, 91 (22) e2104-e2105; DOI: 10.1212/WNL.0000000000006563