Timothy C. Hain, MD
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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, 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. 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 malatal 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.
There are two forms of PM. Ordinary PM is caused by a lesion in the triangle of Guillain Molleret (1933), which is composed of the inferior olivary nucleus in the brainstem, the central tegmental tract which connects the olive to the red nucleus in the midbrain, and through the superior olivary peduncle to the contralateral dentate nucleus of the cerebellum. It is felt that the inferior olive enlarges and develops rhythmic discharges 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 Mollert 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) in the triangle of Guillain Molleret. 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).
When the eyes are involved (25%) there is a pendular nystagmus, which can be horizontal, vertical or rotatory. 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.
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).
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:
Dilantin and barbiturates have been tried unsuccessfully in ordinary PM.
Surgical treatment has been attempted to alleviate ear clicks. Plugging of the eustachian tube and perforation of the tympanic membrane have been tried and failed. Cutting of the levator palatini muscle or the tensor veli palatini have been reportedly associated with partial relief.