Hypertrophic olivary degeneration: A comprehensive review focusing on etiology

Hypertrophic olivary degeneration (HOD) is a rare form of trans-synaptic degeneration characterized by hypertrophy of the inferior olivary nucleus situated in the olivary body, part of the medulla oblongata, representing a major source of input to the cerebellum. HOD typically results from focal lesions interrupting connections from the inferior olive within the dentato-rubro-olivary pathway (DROP), a region also known as the Guillain-Mollaret triangle (GMT) (red nucleus, inferior olivary nucleus, and contralateral dentate nucleus). Clinically, HOD presents classically as palatal tremor and can include dentatorubral tremor and/or ocular myoclonus. Oppenheim first described the enlargement of the ION in his post-mortem study. Since then, a limited number of cases have been reported in the literatures. Thus, we intended to describe the definition, pathophysiology, clinical features, radiological features, diagnosis, and current management of HOD. We provide a comprehensive review of HOD focusing on etiology. The present review may lead to a better understanding of HOD clinical characteristic with the goal of contributing to existing knowledge of this rare disease.