This article might explain why FCR works for PM. I’ll explain at the end.

Palatal myoclonus secondary to hypertrophic olivary degeneration

by Enrique Palacios, Ewa Wasilewska, Jorge E. Alvernia, Ramon E. Figuero.

A 64-year-old woman with a history of hypertension and stroke presented with palatal tremor and myoclonus 11 months after experiencing a vascular insult in the brainstem. The myoclonus was characterized by rhythmic involuntary movement of the soft palate, uvula, pharynx, and larynx. Magnetic resonance imaging (MRI) detected the presence of an old pontine vascular insult associated with a prominence and abnormal hyperintensity in the area of the right inferior olivary nucleus (figures 1-3). These findings were consistent with hypertrophic olivary degeneration. (1,2)

MRI is the most sensitive modality for the diagnosis of hypertrophic olivary degeneration because of its high diagnostic sensitivity in the area of the brainstem. On imaging, hypertrophic olivary degeneration occurs in three characteristic stages (3-5):

* In the first 4 to 6 months, no significant morphologic change in the olive or signal intensity is seen. This period corresponds with the initial phase of gliosis, demyelination, and vacuolization.

* From 6 months through 4 years, hypertrophy and an abnormal signal intensity of the olive are seen. These findings are related to neuronal and astrocytic hypertrophy (figures 1 and 2).

* After 4 years, the hypertrophy resolves, and abnormal signal intensity can be observed.

No evidence of contrast enhancement is seen during any of these stages.

The differential diagnosis of an abnormal localized signal intensity in the olive and pontomedullary area includes ischemic infarction, demyelination, tumor, an inflammatory process (including sarcoidosis), and focal rhomboencephalitis. A focal, hyperintense, nonenhancing lesion and enlargement of the olivary nucleus with a coexisting pontine lesion suggest an injury of the dentato-rubro-olivary pathway, findings that are consistent with hypertrophic olivary degeneration). (3-5)

[FIGURE 2 OMITTED]

Hypertrophic olivary degeneration is a form of trans-synaptic degeneration caused by an insult to the neuronal connections of the dentato-rubro-olivary pathway (i.e., the triangle of Guillain and Mollaret) by a primary brainstem inury. (1,2) Disruption of this neuronal pathway affects the reflex arc that controls fine voluntary movements, resulting in signs and symptoms such as palatal myoclonus and dentatorubral tremor. (2,3) This type of astrocytic degeneration has been reported in both children and adults; there is no predilection to either sex. (4)

At any given time following a primary brainstem injury, there may be focal enlargement rather than atrophy of the inferior olivary nucleus. This finding is characteristically identified on MRI. However, failure to properly identify the enlargement may result in a misdiagnosis (e.g, a tumor or multiple sclerosis). (1,5,6)

[FIGURE 3 OMITTED]

The Guillain-Mollaret triangle is composed of the dentate nucleus, the red nucleus, and the inferior olivary nucleus. The red nucleus and the ipsilateral inferior olivary nucleus are connected via the central tegmental tract, and the dentate nucleus connects to the contralateral red nucleus through the superior cerebellar peduncle. There are no direct connections between the inferior olivary nucleus and the contralateral dentate nucleus. (1-4) While hypertrophic olivary degeneration can occur with any focal lesion that involves the dentato-rubro-olivary pathway, it is typically associated with lesions that involve the superior cerebellar peduncle (dentatorubral tract), the dentate nucleus, or the central tegmental tract. (2,4)

There are three patterns of hypertrophic olivary degeneration as they relate to the location of the primary lesion. When the lesion is in the dentate nucleus or superior cerebellar peduncle, the olivary degeneration is contralateral. When the primary lesion is in the central tegmental tract, olivary degeneration is ipsilateral, as occurred in our patient. When the lesion involves both pathways, the olivary degeneration is bilatera. (1,6)

Hypertrophy of the olivary nucleus following a primary brainstem injury is believed to represent a combination of cell body enlargement, vacuolation of the cytoplasm, astrocytic proliferation, demyelination, and fibrillary gliosis. (2,6) The degree of the hypertrophic olivary nucleus is variable, depending on the time interval from the insult to the Guillain-Mollaret triangle. As seen on imaging, olivary hypertrophy develops 4 to 6 months after the primary insult, and it may resolve 10 to 16 months later. However, abnormal hyperintensity of the inferior olivary nucleus on T2-weighted MRI may continue for years despite the persistence of the signs and symptoms of palatal myoclonus and dentatorubral tremor. (2-5)

The clinical manifestations of hypertrophic olivary degeneration probably reflect a loss of inhibitory control as a result of disruption of the dentato-rubroolivary pathway. (1-3) The most common symptom is palatal myoclonus, which is characterized by rhythmic involuntary movement of the soft palate, uvula, pharynx, and larynx. (2,6) Other clinical signs and symptoms include dentatorubral tremor, severe myoclonus of the cervical muscles and diaphragm, and symptoms of cerebellar or brainstem dysfunction. (2) The central tegmental tract has several connections to the nucleus ambiguous, which gives rise to efferent motor fibers of the vagus nerve that innervates the muscles that control palatal movement. (2,5) Our patient exhibited the classic signs and symptoms of palatal myoclonus, which correlated with imaging findings involving the central tegmental tract.

Not all patients with hypertrophic olivary degeneration develop the classic symptoms, but virtually all patients who develop palatal myoclonus after a brainstem insult will develop hypertrophic olivary degeneration. (1,2) Hypertrophic olivary degeneration is a sequela of a brainstem injury of various etiologies, and its clinical presentation is variable. Identification of the characteristic MRI findings of the olivary nucleus indicating an associated lesion involving the dentatorubro-olivary pathway allows for correct diagnosis. Therefore, it is important to understand the potential clinical pattern that may lead to recognition of the MRI findings of hypertrophic olivary degeneration.

References

(1.) Salamon-Murayama N, Russell EJ, Rabin BM. Diagnosis please. Case 17: Hypertrophic olivary degeneration secondary to pontine hemorrhage. Radiology 1999;213(3):814-17.

(2.) Krings T, Foltys H, Meister IG, Reul J. Hypertrophic olivary degeneration following pontine haemorrhage: Hypertensive crisis or cavernous haemangioma bleeding? J Neurol Neurosurg Psychiatry 2003;74(6):797-9.

(3.) Hirono N, Kameyama M, Kohayashi Y, et al. MR demonstration of a unilateral olivary hypertrophy caused by pontine tegmental hematoma. Neuroradiology 1990;32(4):340-2.

(4.) Uchino A, Hasuo K, Uchida K, et al. Olivary degeneration after cerebellar or brain stem haemorrhage: MRI. Neuroradiology 1993;35(5):335-8.

(5.) Osborn AG, Blaser SI, Salzman KL. Toxic/metabolic/degenerative disorders, acquired. In: Osborn AG, Blaser SI, Salzman KL. Diagnostic Imaging: Brain. Salt Lake City: Amirsys; 2004.

(6.) Kitajima M, Korogi Y, Shimomura O, et al. Hypertrophic olivary degeneration: MR imaging and pathologic findings. Radiology 1994;192(2):539-43.

Enrique Palacios, MD, FACR; Ewa Wasilewska, MD; Jorge E. Alvernia, MD; Ramon E. Figueroa, MD, FACR

From the Department of Radiology (Dr. Palacios and Dr. Wasilewska) and the Department of Neurosurgery (Dr. Alvernia), Tulane University Hospital and Clinic, New Orleans; and the Department of Radiology, Medical College of Georgia, Augusta (Dr. Figueroa).