Pearls & Oy-sters: Progressive ataxia and palatal tremor

Discussion

PT (formerly known as palatal myoclonus) is a rare movement disorder consisting of rhythmic movements of soft palate and comprises 2 forms: EPT and SPT.¹ The name palatal tremor was formally coined in 1990 at the First International Congress of Movement Disorders based on characteristics of the movements, which were considered to be more regular and continuous, like a tremor, and less shock-like, which would be typical of myoclonus. There are some features that are consistent with myoclonus, such as variability.² PT may be unilateral, bilateral, or asymmetric, with partial or complete rhythmicity at a reported frequency of 100–150/min.^3,4 During sleep, PT mostly ceases in EPT in about 50% of the cases but is invariably present in all patients with SPT.^2,5

EPT occurs without an obvious structural lesion in the brain^6,7 and is characterized by rhythmic movement of anterior soft palate, attributable to contractions of the trigeminal nerve–innervated tensor veli palatini muscle, and not uncommonly auditory clicks.⁷ SPT is often associated with a brainstem or cerebellar lesion involving the dentato-rubro-olivary pathway (Guillain-Mollaret triangle).^1,3,5,6 In SPT, palatal movements result from activation of the levator veli palatini muscle. EPT is often associated with ear clicks; however, levator veli palatini activity can also result in audible clicks. Therefore, presence of ear clicks alone cannot differentiate between EPT and SPT.^5,7 Extrapalatal manifestations are seen with this movement disorder, including ocular disorder and extremity and gait ataxia.^5,7

The most common etiologies of PT are stroke, trauma, demyelinating lesion, and posterior fossa tumors.⁷ Histopathologic examination in PT shows enlarged and vacuolated neurons, increased number and size of astrocytes, and fibrillary gliosis in the region of hypertrophic inferior olivary degeneration.⁵ These changes appear on MRI as olivary hypertrophy. It has been reported that MRI T2 changes occur 1 month after the inciting event and are usually present for 3–4 years.⁶ It is not unusual for the affected ION to atrophy over time.⁷

Contrast enhancement is generally associated with malignancy, infection, or subacute phase of ischemic infarction. We are aware of only one case describing hypertrophic olivary degeneration (HOD) with enhancement, which occurred after surgical excision of a medulloblastoma, and therefore the mechanism could have been related to the surgical intervention.⁸ Our patient has no confounding history of tumor, demyelinating lesion, inflammatory processes, Alexander disease, stroke, or surgical intervention, making the point even stronger that contrary to prior reporting,^8,–,10 contrast enhancement of the ION may occur with HOD, and therefore enhancement does not distinguish between HOD and other diagnoses such as malignancy or infectious processes.

PAPT as described here is a subgroup of SPT that is further subdivided into sporadic and familial forms.⁷ Features used to distinguish sporadic PAPT, as in this case, include abnormal eye findings (saccadic pursuit, pendular nystagmus), olivary degeneration, and progression of ataxia. Familial PAPT does not demonstrate olivary hypertrophy. Reported causes of familial PAPT include Alexander disease, polymerase gamma mutation, and spinocerebellar ataxia type 20.⁵ The most problematic symptoms in PAPT include visual disturbance, dysarthria, dysphagia, appendicular and gait ataxia, and other features associated with cerebellar syndromes.⁷ There is no reported effective treatment to prevent or halt the progression of ataxia, the most disabling symptom of PAPT.

Despite recognition of the changes on MRI scan and the histopathology, the natural history of PAPT is unknown. We describe a patient who had spontaneous resolution of PT but continued progression of gait ataxia. This supports data that pathologic changes in the ION are associated with the development but not the maintenance of PT.¹¹ In our review of the literature, we found few cases that describe PAPT and this case is unique in that the patient had spontaneous resolution of PT but continued progression of ataxia and persistent atrophy of the ION as judged by MRI. The patient's imaging was unique in demonstrating HOD with gadolinium enhancement in the absence of tumor, stroke, or surgical intervention.