In HOD, a portion of the brainstem called the inferior olivary nucleus initially enlarges. The inferior olivary nucleus is part of the olivary body, an olive-shaped structure on either side of the brainstem. The olivary body assists in cerebellar motor learning and functioning. When the inferior olivary nucleus enlarges, it irritates a motor pathway called the dentate-rebro-olivary pathway (or Guillian-Mollaret triangle). Over time, the olivary nucleus stops enlarging and instead atrophies, but the symptoms persist.
The hallmark symptom of HOD is a rhythmic tremor of the palate and/or other structures in the throat. The palatal tremor may be accompanied by oscillating nystagmus in which the pupil of the eye involuntarily moves in circles. HOD can also include ataxia, clicking tinnitus, and tremor in other parts of the body. These are in addition to any deficits caused by the original hemorrhage or surgery; HOD symptoms typically emerge months after surgery or hemorrhage.
There is no direct treatment for HOD, but medications may help manage symptoms for some people. The most commonly used are gabapentin and memantine to reduce the amplitude and speed of the oscillations of the pupil. Palatal tremor has been treated with trihexyphenidyl.
To learn more, visit the National Institutes of Health HOD information page.
For patients seeking HOD support, an Angioma Alliance member has set up a Hypertrophic Olivary Degeneration (HOD) Patients and Family Facebook Group.
Last updated 3.21.20