Objective: To report a patient with L-dopa-responsive, diurnally fluctuating auricular tremor with tetrahydrobiopterin (BH4) deficiency.

Background: Although segmental dystonia of the cranial muscles is recognized, isolated involvement of auricular muscles are extremely rare. Although some reported cases under the name of auricular myoclonus or “moving ear syndrome” are attributed to a spectrum of palatal myoclonus with ear clicks, most of them are not associated with any known pathologic conditions. Our patient is the first case of bilateral auricular tremor associated with BH4 deficiency.

Methods: Case report with video, neurophysiology, and biopterin analysis.

Results: The patient is a 34-year-old Japanese man with normal developmental milestones who presented with abnormal movement of both ears in 2012. Neurological examination demonstrated rhythmical bilateral ear movements. No other abnormal neurological signs were present. He did not show cognitive impairment, ataxia, spasticity, or limb dystonia. Neither palatal myoclonus nor ear clicks were present. Surface EMG showed rhythmical synchronized contraction of bilateral retroauricular muscles of around 2.5 Hz. EEG, brain MRI, 123I-FP-CIT SPECT and 123I-MIBG myocardial scintigraphy were normal. With time, the tremor spread to occipitalis muscles moving synchronized with the retroauricular muscles demonstrated by surface EMG. The following medications were either not beneficial or tolerated: diazepam, clonazepam, trihexyphenidyl, carbamazepine, and arotinolol hydrochloride. Botulinum toxin injection had some effect, although the effect is limited and variable. In three years from onset, the patient noticed that he was symptom-free for about half an hour after sleep. Thus biopterin analysis was conducted with his serum, cerebrospinal fluid (CSF) and urine. CSF contained elevated biopterin and decreased BH4 without elevated serum phenylalanine, consistent with sepiapterin reductase deficiency (SRD). Treatment with L-dopa resulted in marked clinical improvement and the bilateral auricular tremor disappeared.

Conclusions: This is a rare case of isolated adult-onset bilateral auricular tremor. It is also the first report of auricular tremor associated with BH4 deficiency. SRD and other BH4 defiencies should be considered in unexplained movement disorders, as they are treatable with L-dopa and other monoamine/neurotransmitter treatments.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/l-dopa-responsive-diurnally-fluctuating-auricular-tremor-with-tetrahydrobiopterin-bh4-deficiency/