Superior Oblique Myokymia

Abstract

Most patients have had the classic bursts of smallamplitude, high-frequency rotary oscillations causing oscillopsia, defined as intermittent uniocular microtremor [8}. Others, however, have had a slower, larger-amplitude intorsional movement causing vertical and torsional diplopia. We have termed this movement macrorota y deviation (MRD). MRD has occurred most often in association with the more classic IUM C6-8, 10, 111, but in a few patients it has been the only or predominant eye movement abnormality C2, 7, 121. Other associated motility problems have included intermittent overaction of the ipsilateral superior oblique muscle 110-121, ipsilateral superior oblique paresis ( 7 , 101, and, in our patient, an intermittent Brown's syndrome.We suspect that all of the grossly visible movements (MRD, intermittent overaction of the superior oblique, and intermittent superior oblique tendon sheath syndrome) represent the same rotary entasia expressed differently when assessed by varying techniques. An alternate-cover test would reveal an overaction of the superior oblique muscle; an apparent Brown's syndrome would be diagnosed if the motor anomaly occurred during attempted gaze inward and upward; and the MRD itself would be observed only during direct observation.The cause of IUM and MRD is unclear. Their frequent concurrence implies a continuum of motor anomalies. Electromyographs of the two types of movements are similar, with evidence of chronic denervation, supporting the idea that both are manifestations of superior oblique myokymia [7, 91. Kommerell's patient with MRD had a more stable rate of firing than others with IUM, suggesting that the firing pattern of the abnormal motor units may determine the clinical picture E91. All electromyographic evidence to date supports Hoyt's original suggestion that SOM is primarily a nuclear disorder C7-91.Possibly pertinent to SOM is a report by Baker and Bertoz, who evaluated oblique nystagmus induced by vestibular lesions in alert "encephale isole" cats C11.Using intra-and extracellular recordings from inferior and superior oblique motor neurons, they noted a "rhythmic oscillation" in the electrical discharge from the oblique motor neurons immediately after a sudden decrease in the stimulation rate. The occurrence of such a "rhythmic oscillation" immediately after a sudden decrease in the stimulation rate could be the physiological basis for the clinical observation that the uniocular microtremor is most easily provoked by moving the eye into and then out of the field of action of the superior oblique muscle.The authors wish to thank Dr J. Lawton Smith for referring his patients to us for follow-up.

Superior oblique myokymia

“…Daily doses of 600 to 900 mg may be required. Carbamazepine was the first medication used successfully in the treatment of SOM and, in our opinion, could be the second treatment choice [19]. In our experience, it has been quite effective; doses of 200 mg three times daily may be used.…”

Results of extraocular muscle surgery for superior oblique myokymia

“…Medical treatment options include oral carbemazepine, phenytoin sodium, clonazepam, baclofen, gabapentin and propranolol, and topical beta-blockers (Timolol maleate, betaxolol), all of which have been reported to have variable success. [5][6][7][8][9][10][27][28][29] In some patients treatment was not successful; in others the benefit was temporary, and numerous patients did not tolerate the medication due to side effects. Carbamazepine is the most frequently reported medication used followed by topical beta-blockers.…”

“…2,3,5,7,[14][15][16][17][18] Although many of these studies mentioned some patients having diplopia after surgery, most did not describe the ocular alignment or symptoms outside the primary position. 2,3,5,15,17,18 Only the 3-case report by Palmer and Shults 16 and the 1-case report by Susac and colleagues 5 provided detailed measurements of ocular alignment in the diagnostic gaze positions as well as in the reading position (downgaze at 1 ⁄ 3 meter).The purpose of this study is to report our experience with a large series of patients undergoing surgery for SOM after medical treatment(s) failed, with particular attention to postoperative alignment and the presence of diplopia in the 9 diagnostic fields of gaze at 6 meters, on head tilt right and left, and in the reading position. …”

“…3 Many patients have spontaneous relapses and remissions over years and symptoms can be exacerbated by stress, caffeine, or nicotine. 3 Treatment options for patients with SOM are both medical 4-10 and surgical, 2,3,5,7,[11][12][13][14][15][16][17][18][19] with surgery being recommended only after medical treatment has failed. Although neurovascular decompression of the trochlear nerve has been reported as a treatment for SOM, [11][12][13] most reports of surgical management describe extraocular muscle surgery in the form of weakening the ipsilateral superior oblique and inferior oblique.…”

Localised unilateral blepharochalasis.

“…2 The condition consists of recurrent attacks of oedema of the eyelids and in chronic conditions the skin becomes reddish, thin, and redundant. Periorbital sequelae include ptosis, pseudoepicanthic fold with underlying nasal fat pad atrophy, blepharophimosis, proptosis, lower lid malpositions, lacrimal gland prolapse, and cysts.…”