Olivary Hypertrophy Induced Palatal Myoclonus in a Treated Case of Medulloblastoma

Palatal Myoclonus after Posterior Fossa Surgery in a Child with Medulloblastoma

A 15-year-old female presented in the outpatient department with persistent sensation of involuntary movements of palate for 2 months. She underwent surgery for a posterior fossa mass 6 months prior, which was confirmed to be a medulloblastoma on histopathology. On examination, palatal myoclonus was observed ([Video 1]), which was present even during sleep. Magnetic resonance imaging brain showed hypertrophy of the bilateral inferior olivary nuclei ([Fig. 1]).

Fig. 1 (A) T2W axial image at the level of medulla shows evidence of hypertrophy of bilateral inferior olivary nuclei (black arrows). (B) Axial FLAIR image at the level corresponding to (A) reveals hypertrophied bilateral inferior olivary nuclei (white arrows). (C) Axial T2W image and (D) axial FLAIR image show atrophy of the cerebellar hemispheres (arrow). Gliotic changes (asterisk) are noted in the cerebellar vermis and paravermian cerebellar hemispheres, these changes are secondary to resection of the posterior fossa tumor. No residual tumor was seen. Preoperative (E) axial T2W image and (F) ADC MRI images demonstrating a well-defined lobulated posterior fossa mass (arrows) in midline which is showing diffusion restriction suggesting the diagnosis of medulloblastoma. ADC, apparent diffusion coefficient; FLAIR, fluid attenuated inversion recovery; MRI, magnetic resonance imaging.

Video 1 Clinical video showing palatal myoclonus.

Palatal myoclonus is mostly caused by space-occupying lesion in the Guillain–Mollaret triangle, formed by dentate nucleus, red nucleus, and inferior olivary nucleus.[1] Any insult (e.g., infarction, trauma, or neoplasm) interrupting this pathway causes hypertrophic olivary degeneration (HOD), which typically presents as oculo-palatal myoclonus with associated ear clicking in some patients.[1] In our case, the patient presented only with palatal myoclonus. HOD is a rare complication after posterior fossa tumor surgery.[2] HOD after posterior fossa surgery usually presents with posterior fossa syndrome (“cerebellar mutism”) rather than typical oculo-palatal myoclonus, unlike in our case.[3] To the best of our knowledge, palatal myoclonus has never been reported in postsurgical cases of pediatric medulloblastoma. Also, HOD is usually unilateral but a midline lesion involving the decussating fibers can result in bilateral HOD, as in the index case.[3] Many drugs, such as baclofen, have been shown to have variable benefits.[4]

Consent

An informed and written consent from the patient's guardian was taken for the publication of this report.

Ethical Approval

The institutional ethical review board granted a waiver for ethical clearance for this report as no ethical issues were found.

Publication History

Received: 23 April 2024

Accepted: 22 May 2024

Article published online:
19 June 2024

• References

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