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Timothy C. Hain, MD. 
Page last modified:
November 21, 2009
Movie of Palatal Myoclonus (5 meg) (Examiner is holding a camera pointing towards back of throat of patient with PM). This individual was largely normal, other than having OPM.
Another movie of palate in oculopalatal myoclonus (14 meg). This individual has a degenerative nervous system disorder.
Movie of pendular nystagmus in oculopalatal myoclonus (7 meg).
Palatal myoclonus (PM) is characterized by rhythmic involuntary jerky movements of the soft palate of the throat, and also sometimes other muscles related to the throat. When associated with eye movements, as is not unusual, it is called "oculopalatal myoclonus", or OPM. A clicking sound is commonly heard. The frequency of the jerking is ordinarily 1-2 hz. PM is exceptional among movement disorders because of persistence during sleep and frequently lack of modulation by voluntary influences. This likely results from it's mechanism which is not mediated via the basal ganglia but rather is driven by a low-level oscillator in the brainstem.
The youngest reported case is 18 months, and the oldest, 91 years old. Unsteadiness and tremor is common in persons with OPM.
Example case: A 72 year old woman came to medical attention when she developed inward turning of her left eye. An MRI scan was obtained which documented a vascular malformation in her pons. An operation was attempted, following which she developed near complete paralysis of horizontal eye movements. Balance was poor and one eye began to "bob". On an examination done one year later, there was a constant pendular (sinusoidal) nystagmus of one eye, severe unsteadiness, and a one cycle/second up and downward movement of the soft palate (palatal myoclonus), accompanied by contractions of muscles in the throat. The combination of the "bobbing" ocular nystagmus and palatal myoclonus, defines a case of OPM. The cause is presumably related to interruption of the central tegmental tract (see below). Click here for other cases.
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The triangle of Guillain-Mollaret -- Source: http://www.mni.mcgill.ca/neuroimage/apr2001/apr2001_p7.htm |
Another schematic of the triangle of Guillain-Mollaret -- source: http://www.neurology.org/cgi/content/full/71/4/301/F119. This view is a coronal view mainly showing the brainstem. |
There are two forms of PM. Ordinary PM is caused by a lesion in the triangle of Guillain-Mollaret (1933). Guillain and Mollaret were French neurologists, and perhaps this is why much of the literature is from French authors. At any rate, this triangle (see figure above) is found in the brainstem -- and it is composed of the inferior olivary nucleus in the medulla of the brainstem, the central tegmental tract which connects the inferior olive to the red nucleus in the midbrain, the inferior cerebellar peduncle which connects the inferior olive to the cerebellum, the superior cerebellar peduncle which connects the red nucleus to the contralateral dentate (or dental) nucleus of the cerebellum. The red nucleus and inferior olive are generally thought to be "outboard" cerebellar nuclei, while the dentate nucleus is within the substance of the cerebellum. The superior olive is not involved in PM, but rather has to do with sound processing.
It is felt that the inferior olive enlarges and develops rhythmic discharges of between 0.5 to 3 hz, when it is denervated by ipsilateral brainstem disease or contralateral cerebellar disease, and is responsible for the palatal myoclonus. The inferior olive is provided with a massive inhibitory (GABA) projection from the cerebellar nuclei. This differs from most other cerebellar output which is excitatory. Olivary neurons are extensively coupled by gap junctions, which may account for their tendency to oscillate when inhibition is released (Mugnaini and Nelson, 1989).
The lesion in the triangle of Guillain Mollaret may be caused by a variety of structural disorders . Considering all PM, both ordinary and essential, the breakdown by percentage is stroke (40%), tumor (7%), trauma (8%), MS(8%), encephalitis (2%), and degenerative disease (2%) (percentages taken from Deuschel, 1990). There frequently is an asymptomatic period of roughly a year between the advent of a structural lesion such as a stroke, and appearance of the PM. Ordinary PM has an age peak of 50-60.
Essential PM is the phenotype of PM, without an obvious lesion (usually on MR imaging) in the triangle of Guillain Mollaret. Roughly 27% of all PM is essential. Essential PM may be more variable than PM, and sometimes can be stopped by intention of the patient, modified by neck position, or eliminated on mouth opening. The cause of essential PM is unclear. Essential PM has an age peak of 30-40. The eyes are rarely involved in essential PM (the author has seen a very subtle case).
It seems likely to us that OPM and essential PM are structurally different conditions, one which is due to a pattern generator in the brainstem, and the other which is due to peripheral irritibility in a sensory feedback loop involving the palate.
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Vertical pendular nystagmus associated with oculopalatal myoclonus syndome.
Recording method: infrared video. Click here to see the movie of this segment. (c) 2003-5 Timothy C. Hain, M.D. All rights reserved |
When the eyes are involved (25%) there is a pendular nystagmus (see above) which can be horizontal, vertical or rotatory. To see a 1-meg movie, click here. The nystagmus may respond to valproic acid (Lefkowitz and Harpold, 1985). It has also been reported to be successfully treated with INH (200 mg BID to QID, with pyridoxine) combined with converging prisms.
When the limbs are involved (about 10%), there is commonly a pendular tremor time locked to palatal movements.
Symptomatic and essential palatal myoclonus were extensively reviewed in an article by Deuschel and others, 1990.
Palatal myoclonus is a clinical diagnosis and the differential diagnosis is very limited. Whipple's disease is associated with an oculomasticatory myorhythmia. In these cases the eyes have a pendular vergence oscillation accompanying paralysis of vertical gaze, and there are contractions of the masticatory muscles. The vergence nystagmus differentiates this disorder from PM. Intestinal biopsy establishes the diagnosis in Whipples. Hashimoto's encephalitus has been reported to cause PM (Erickson et al, 2002), but like Whipples disease, this is exceedingly rare.
Tests that we recommend in all persons with palatal myoclonus:
No other laboratory testing is routine in PM, but there are some investigational possibilities.
Nemni et al (1994), suggested that anti-glutamic acid decarboxylase antibodies ("anti-GAD") should be obtained in cases of essential PM. This test is available as a "send-out" test, to be collected in a gold top. Anti-GAD is also often positive in diabetes, and in a rare neurological condition, the so-called "stiff man syndrome". Anti-GAD has also been reported in several patients with cerebellar ataxia (Abele et al, 1999).
As PM has been reported in Hashimoto's encephalitis, anti-microsomal antibodies as well as anti-TPO and anti-thyroglobulin antibodies may also be considered.
In patients with symptomatic palatal myoclonus, generally no treatment works. In reported papers, about 20% of treatments have been successful, but some indicate that no treatment works. There are sporadic reports however of successful treatment with the following medications:
As somewhat of a summary of the authors judgement about these things, for the central version of PM, drugs worth trying are baclofen, gabapentin, memantine and clonapin, as they all have a reasonable chance of working and relatively few side effects. If one wants to exhaust all possibilities, the others on the list may be worth considering with considerable caution. We are dubious that any medication other than those useful for neuralgia (some of the anticonvulstants) will be useful in the peripheral form of PM.
Although anticholinergics such as trihexyphenidil (Artane) have been reported useful in acquired pendular nystagmus (Jabbari et al. 1983; Jabbari et al. 1987), we have had no success. Neither did Leigh et al (1991). Problems include lack of efficacy and severe side effects.
Seizure medications -- as a general comment, one would expect these medications might possibly work in the "peripheral" type of PM (without nystagmus), where their mechanism would be similar to a medication used for neuralgia. For the central type of PM (with nystagmus), GABA agonists might be useful.
Memantine, a recently avaialble drug in the USA, has been reported useful in 9 patients with pendular nystagmus due to MS (Starck, Albrecht et al. 1997). We have not found it helpful in a single patient trial on a vertical pendular nystagmus associated with palatal myoclonus.
Cannibis has been reported useful in suppressing pendular nystagmus in multiple sclerosis. (Schon, Hart et al. 1999; Dell'Osso 2000).
Surgical treatment has been attempted to alleviate ear clicks.
A newer method of treatment that seems logical to us is the use of Botulinum toxin to paralyze the tensor veli palatini (Bryce and Morrison, 1998; Varney et al, 1996). We have had excellent success with this treatment for palatal motion in our clinic setting in Chicago. It does nothing for the nystagmus however and it also is a temporary (4 month) fix. In persons who respond to Botox, after several relapses, some authors have gone on to use of destructive procedures (e.g. Aydin et al, 2006).
Mondria et al reported successful treatment with a "simple dental device" (2007). While interesting, we are dubious that this method of treatment is generally useful.
| © Copyright November 21, 2009 , Timothy C. Hain, M.D. All rights reserved. Last saved on November 21, 2009 |