Successful Treatment of Superior Oblique Myokymia With Cannabidiol Oil

Superior oblique myokymia (SOM) is a rare condition characterized by sudden episodes of involuntary, rhythmic, monocular contractions of the superior oblique muscle, resulting in diplopia and oscillopsia (1). Published SOM medical therapies include beta-blockers, carbamazepine, oxcarbazepine, gabapentin, phenytoin, and botulinum toxin injection (1). However, its low prevalence, unknown etiology, and variable time course make SOM a particularly difficult condition to study and there are currently no well-established treatments. We present a case of SOM successfully treated with cannabidiol (CBD) oil. CASE REPORT A 26-year-old man was referred to the neuro-ophthalmology service for oscillopsia in his right eye. He reported a three-week history of “shaking” of vision in his right eye and intermittent vertical binocular diplopia, both worse when looking down. On examination, he had normal afferent visual function. Slit-lamp examination revealed low-amplitude, high-frequency bursts of incyclotorsion of the right eye. This was more obvious in downgaze and corresponded with his subjective symptoms. Maddox rod testing during episodes of diplopia revealed a right hypotropia that resolved when he was asymptomatic. Extraocular movements were otherwise full and the remainder of his cranial nerves were normal. A clinical diagnosis of right SOM was made and a brain MRI did not show any lesion along the course of the trochlear nerves. The patient underwent unsuccessful treatment with timolol and levobunolol eye drops. After a self-directed literature review and discovering that cannabidiol may reduce seizure frequency in treatment-resistant epilepsy, he self-initiated oral CBD oil 60 mg every 3 hours. He found a predictable response of decreased oscillopsia amplitude and frequency that occurred 30–45 minutes after CBD oil use that lasted for 4 hours. A cannabinoid specialist was consulted and he titrated the CBD oil to 0.7 mL (25 mg CBD 2 mg THC/1 mL) 3 times per day. The oscillopsia continued to resolve in a timely manner after initiation of treatment. The patient continued regularly using CBD oil for a total of 3 months, after which he was essentially symptom free and able to return to work. On a follow-up assessment 7 months later, he was orthophoric and remained symptom-free, only sparingly using CBD oil. DISCUSSION Although SOM is a condition that may resolve spontaneously, we postulate that oral CBD oil played a significant role in our patient's symptom resolution, given the predictable response in his oscillopsia reduction after using CBD oil and the close temporal relationship between symptom relief and CBD oil administration. In addition, the patient was treated unsuccessfully with topical beta-blockers, further reducing the likelihood that improvement of his SOM was spontaneous. Previous reports on the use of CBD oil are limited to an online discussion forum, where there was an anecdotal report of persistent SOM successfully treated with CBD oil in 2018 (2). She has been symptom-free for over a year. For other involuntary ocular movement disorders, there are 2 published cases of nystagmus suppression after smoking cannabis (3,4). Schon et al (3) report a patient with pendular nystagmus in the context of MS who experienced dramatic dampening of his oscillopsia 30 minutes after smoking 2 cannabis-containing cigarettes. This effect lasted 4–5 hours, and there was a correlation of therapeutic benefit with serum cannabinoid levels. Dell'Osso also observed a patient with congenital nystagmus whose nystagmus dampened after smoking cannabis (4). Δ9-tetrahydrocannabinol (THC) is the most well-studied cannabinoid, but is well known for its psychoactive affects. However, CBD is not associated with psychoactivity and does not affect memory or motor function (5). It has been reported to be of benefit in a number of neurodegenerative disorders such as Alzheimer disease and Parkinson disease, epilepsy as well as anxiety and depression (5). It may also offer therapeutic benefits for spasticity, pain, and sleep disorders (5). The exact mechanism by which CBD exerts its anticonvulsant effects is unknown but may be related to its ability to reduce neuronal excitability through modulation of intracellular calcium (6). Furthermore, THC and CBD act on cannabinoid receptors of the endocannabinoid system, specifically cannabinoid type 1 (CB1) and type 2 (CB2) receptors, which are present in the central and peripheral nervous systems. Cannabidiol was identified as a negative allosteric modulator of the CB1 receptor and is hypothesized to have the potential to treat central nervous system disorders while avoiding the adverse effects associated with THC's orthosteric agonism (7). Other receptors through which CBD may exert its effects include the transient receptor potential of vanilloid type 1 channel, 5-HT1A serotonergic receptor, and alpha-1 and alpha-2 glycine receptors (6). Extensive study in this area is ongoing (5). Further study in a larger patient group is needed before its place in the SOM treatment algorithm can be established. At the present time, CBD oil can be used after failure of traditional treatment such as beta-blockers, carbamazepine, or gabapentin, or can even be considered as initial therapy due to its favorable safety profile and lack of psychoactivity. Factors limiting its use are cost and availability in certain regions. Significant adverse effects have not yet been described with its use (5). SOM is a challenging condition to treat and response to therapy varies depending on the individual. This case contributes an additional therapeutic agent that may be trialed in SOM and adds to the literature on the role of CBD in neurological conditions. STATEMENT OF AUTHORSHIP Category 1: a. Conception and design: S. Labbé and J. A. Micieli: b. Acquisition of data: J. Ma, S. Labbé, and J. A. Micieli; c. Analysis and interpretation of data: J. Ma and S. Labbé. Category 2: a. Drafting the manuscript: J. Ma; b. Revising it for intellectual content: S. Labbé and J. A. Micieli. Category 3: a. Final approval of the completed manuscript: J. A. Micieli.

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