Hypertrophic Olivary Degeneration Following Brainstem Hemorrhage in a Patient with Tremor: A Case Report with Serial MRI Follow-Up.

Background: Hypertrophic olivary degeneration (HOD) is a rare neurological condition resulting from trans-synaptic degeneration of the inferior olivary nucleus (ION) following disruption of the dentato-rubro-olivary pathway, also known as the Guillain-Mollaret triangle (GMT). Although the clinical and radiologic features of HOD have been previously described, the precise temporal correlation between clinical symptom onset and manifestations on magnetic resonance imaging (MRI) remains difficult to establish, and the factors contributing to accelerated disease progression are poorly understood. Case Presentation: A 43-year-old male presented with intracerebral hemorrhage involving the left midbrain, bilateral pons, and cerebellum. Serial MRI was prospectively performed starting four weeks post-hemorrhage, at which time no signal abnormalities were detected in the ION. However, at 9 weeks, T2 hyperintensity first emerged in the bilateral ION. Approximately 2 weeks after this finding, the patient developed characteristic palatal and lingual tremors, accompanied by a dissociated vertical pendular nystagmus that was predominantly monocular (right eye). In addition, severe dysphagia was also noted, with videofluoroscopic swallowing study (VFSS) showing aspiration across all diets. A subsequent MRI obtained at 13 weeks post-insult (two weeks after tremor onset) revealed newly developed bilateral ION hypertrophy, with the maximal diameter increasing from a 5 mm baseline to 7 mm. Follow-up MRI at 17 weeks post-hemorrhage revealed further progression with increased hypertrophy and signal intensity. Dysphagia persisted throughout the clinical course, ultimately necessitating percutaneous endoscopic gastrostomy (PEG) tube insertion. Conclusions: This case provides rare, longitudinal documentation of the clinico-radiologic progression of HOD, facilitated by a pre-insult baseline MRI and prospective serial imaging. Our findings provide a detailed timeline of the transition from signal abnormality to hypertrophy in correlation with clinical symptom emergence.