Hypertrophied Atrophy: Two Patient Case Report of Post-stroke Post-gamma Knife Radiosurgery Hypertrophic Olivary Degeneration

The study on patients presenting with tremors gives us deep knowledge of the connections in the motor circuits of the basal ganglia and brainstem. The large amplitude, low frequency tremors involving the limbs which has been variedly described as bird flapping or an alien hand movement of limbs is the rubral tremor associated with disturbances in the brainstem circuit involving the structures of Guillain–Mollaret triangle (GMT) which include red nucleus, dentate nucleus and the inferior olivary nucleus (ION). The afferent cut off to the ION results in pathological degeneration with volumetric expansion of the nucleus observed radiologically or also called the hypertrophic olivary degeneration (HOD). Two patients with different aetiologies of pontine bleed and ION afferent disconnection presented with a delayed rubral tremor. Both showing T2/FLAIR magnetic resonance imaging hyperintense signal in the olivary nucleus on the same side of the primary pathology completing the aetio-clinico-radiological diagnosis of HOD. Case literature is limited to few single case reports, and amongst them, the most common aetiologies include the vascular pathologies such as brainstem bleed, infarct or cavernous malformation or it has been observed post-tumour excision near the brainstem. The 2nd case in our report is the 1st such report of a gamma knife radiosurgery (GKRS) induced HOD. Sound knowledge of brainstem anatomy and physiological pathways involved in motor activity and judicious intervention of areas either surgically or by GKRS is essential to avoid HOD-related sequalae. In the patients presenting with rubral tremors, HOD must be kept in mind owing to its self-limiting natural history and partial response with dopaminergic agents and sodium valproate.