Hypertrophic olivary degeneration: A clinico-radiologic study

Introduction: The frequency and causes of hypertrophic olivary degeneration (HOD) are unknown. We compared the clinical and radiological characteristics of unilateral HOD and bilateral HOD. Methods: We performed a search of a radiologic report database for patients who were radiologically diagnosed as having HOD. This database includes the patients examined at the Mayo Clinic in Florida and Arizona. We used the search terms "hypertrophic olivary degeneration", "HOD", and "olivary" in the reports recorded from 1995 to 2015. Pertinent medical records and magnetic resonance imaging (MRI) scans of the brain for those with HOD were reviewed retrospectively. Results: We identified 142 MRI studies on 95 cases who had radiologically proven HOD, 39 cases had unilateral HOD and 56 with bilateral HOD. In symptomatic cases, the most common symptom was ataxia. Palatal tremor was observed in almost half of all HOD cases. While cerebrovascular diseases were the most frequent etiology in both types of HOD (n = 24, 62% in unilateral; n = 17, 30% in bilateral), more than half of bilateral HOD cases had an unknown etiology (52%, n = 29), whereas only 13% (n = 5) of the unilateral cases had an unknown etiology (χ² test, P < 0.001). The lesions of unilateral HOD had a tendency to improve radiologically over time, whereas those associated with bilateral HOD were likely to worsen (χ² test, P < 0.05). Conclusions: Our study showed that bilateral HOD is more common than unilateral HOD. Half of bilateral HOD cases had no obvious cause and some worsened over time. This may implicate a possible primary neurodegenerative process.