11.1 Introduction

Palatal myoclonus (PM) is a movement disorder characterized by involuntary rhythmic muscular contraction of the soft palate. It was categorized as palatal tremor (PT) at the First International Congress of Movement Disorders in 1990, though the terms are often used interchangeably in the literature. ¹ PT is subclassified into symptomatic palatal tremor (SPT) and essential palatal tremor (EPT). SPT is typically one facet of a constellation of symptoms involving the head, neck, and face. SPT is infrequently symptomatic at the level of the palate (8% of cases), and rarely requires medical treatment. By contrast, EPT is frequently symptomatic and usually generates a symptomatic ear clicking tinnitus secondary to involuntary palate contractions. This clicking may be audible to others. Additional symptoms include nonaudible awareness of palatal movements and rhinolalia. ² The end-organ difference between SPT and EPT is thought to be the reason for the variance of symptoms: SPT is posited to involve the levator veli palatini (LVP; cranial nerves IX and X), whereas EPT is presumed to involve the tensor veli palatini (TVP; cranial nerve V) (Fig. 11‑1, Table 11‑1).

Contraction of the tensor is associated with the rapid opening of the eustachian tube, creating a sudden drop in tubal surface tension resulting in the often-described audible snap, crack, or pop (Fig. 11‑2). ³ PT may involve one or both sides of the soft palate, oscillating at a frequency of 0.5 to 300 Hz. The typical age for EPT is 25 to 35 years compared with 45 years for patients with SPT, with an equal male-to-female incidence. ^{1 ,​ 2 ,​ 4} Despite the subclassification of PT into SPT and EPT, there is evidence supporting a spectrum of PT disorders, as some patients do not clearly fit into one subclass or the other. ¹

11.2 Workup

The diagnosis of PM relies on disease history and a neuro-otorhinolaryngologic evaluation. The most common complaint is the characteristic clicking tinnitus, which may be audible to the examiner. In essential PT (which more commonly presents with palatal symptoms), imaging and laboratory evaluations are usually normal. Despite the paucity of diagnostic findings, neurologic assessment is often indicated to define or exclude any associated or underlying abnormality. Symptomatic PT is usually devoid of any palate-specific symptoms, though it is associated with other neurologic movement disorders of the head and neck which may include the larynx, pharynx, face, or other structures controlled by the brainstem or cerebellum. SPT often presents with other clinical findings including dysarthria, nystagmus, and ataxia ¹ and is often synchronous with the extrapalatal myoclonic structures. ⁴ Symptomatic PT warrants a full neurologic evaluation.

The most common form of SPT is secondary to a structural lesion of the brainstem or cerebellum with palatal symptoms developing at a median of 10 months after the injury and persisting throughout life. Hypertrophic olivary degeneration is typically identified on magnetic resonance imaging with increased signal intensity and enlargement of the inferior olive or dentato-olivary tract on T2-weighted/fluid-attenuated inversion recovery and proton-weighted images. ⁵ SPT has been associated with numerous systemic metabolic, immunologic, infectious, and traumatic disorders. Causes of SPT include the following:

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  Hereditary syndrome.

  
  
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  Familial leukodystrophy.

  
  
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  Neurodegenerative disorders.

  
  
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  Vascular: hemorrhagic or ischemic cerebral insult.

  
  
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  Trauma.

  
  
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  Viral encephalitis.

  
  
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  Malaria.

  
  
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  Multiple sclerosis.

  
  
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  Cerebrotendinous xanthomatosis.

  
  
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  Behçet disease.

  
  
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  Krabbe disease.

  
  
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  Sclerosing leukoencephalopathy.

  
  
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  Immunologic.

  
  
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  Brainstem tumors or surgery.

  
  
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  Drug induced.

The potential etiology of EPT is heterogenous with theories supporting the presence of a central mechanism generating the abnormal movement. Local mechanical and inflammatory causes have also been postulated with 40% reporting that myoclonic symptoms began after viral upper respiratory tract infection. ² Some patients can voluntarily elicit the movement and there are a significant number of cases with psychogenic origin. ^{1 ,​ 6}