Parakinesia Brachialis Oscitans in a Patient With a First Manifestation of Multiple Sclerosis.

Objectives: Parakinesia brachialis oscitans (PBO) is the involuntary movement of an otherwise paretic upper limb triggered by yawning. We describe the first case of PBO in a patient with a first manifestation of tumefactive multiple sclerosis (MS). Methods: A 35-year-old man presented to the emergency department with a first episode of generalized seizure. Neurologic examination revealed left-sided spastic hemiparesis, predominantly affecting his upper limb. Brain MRI showed a tumefactive right hemisphere lesion consistent with demyelination. CSF did not document unmatched oligoclonal bands. Results: Two weeks after admission and, despite being unable to voluntarily raise his left arm, the patient noticed a repeated and reproducible involuntary raise of this limb upon yawning, consistent with PBO. In the following weeks, the phenomenon diminished both in frequency and movement amplitude alongside motor recovery. An MRI performed 2 months later showed progression of the demyelinating lesion load and confirmed a diagnosis of MS. Discussion: PBO is an example of autonomic voluntary motor dissociation and reflects the interplay between loss of cortical inhibition of the cerebellum in the setting of functional spinocerebellar pathways. Clinicians should be aware of this transient phenomenon which should not be mistaken as a chronic movement disorder or focal epileptic seizures.