Two-muscle surgical treatment of a compensatory head tilt in an adult with acquired downbeat nystagmus

Abstract

Kestenbaum-Anderson–like operations have proven beneficial in treatment of compensatory head tilt in patients with infantile nystagmus. However, their use in acquired vertical nystagmus in adults with head tilt has rarely been reported. Presented here is a case of a 52-year-old woman with acquired downbeat nystagmus with a significant head tilt who responded to a simple two-muscle surgery involving the superior recti. Cyclovertical muscle surgery should be considered a viable option in such patients who are refractory to medical intervention. Additionally, it appears that four-muscle vertical muscle recessions (two muscles per eye) may not be necessary to dampen vertical nystagmus since good results can be obtained with a single muscle recession bilaterally.

Nystagmus in children and adults is an involuntary oscillatory eye movement disorder that can vary in intensity in different gaze positions. If there is a certain gaze position where the nystagmus is least active, this is known as a null point (or zone), and often the patients’ symptoms and vision improve when the eyes are deviated toward that null point/zone. Patients with an eccentric null point/zone will often assume a compensatory head tilt to set their eyes in that null zone and optimize their vision. This forms the basis of the Kestenbaum-Anderson–like operations, which have proven beneficial in treatment of compensatory head tilt in patients with infantile nystagmus. The Kestenbaum-Anderson procedures involve shifting the eyes in the direction of the abnormal head turn/tilt and away from the preferred direction of gaze. The Kestenbaum procedure involves bilateral recession of the yoke muscles opposite to the head turn, combined with bilateral resection of their antagonists. Anderson’s procedure only involves recession of the yoke muscles. However, the procedure’s use in acquired vertical nystagmus in adults with head tilt has rarely been reported.

CASE REPORT

A 52-year-old woman presented with 3 years of oscillopsia that lessened only when she kept her chin tucked down. Three years prior, she had suffered a stroke that magnetic resonance imaging showed to be bilateral basal ganglia infarcts, with the left lesion located close to the internal capsule (Figure 1). No brainstem lesions were identified on review with neuroradiology. Despite mild residual right-sided weakness, her functionality was primarily limited by visual impairment. Her neurologist had prescribed both clonazepam and gabapentin, which provided minimal benefit. Because of intolerable side effects, she discontinued the gabapentin.

Figure 1.

Magnetic resonance imaging of the brain. (a) Axial diffusion-weighted image. (b) Coronal T2 fast spin echo image corresponding to the line through the axial image.

Uncorrected visual acuity was 20/25 OD and 20/40 OS but she maintained a large chin down position of approximately 20° to 25° to read the Snellen chart. All gaze positions revealed a slow to moderate frequency, moderate amplitude downbeating nystagmus that slightly dampened in down-gaze and significantly dampened in up-gaze. Bilateral 12 prism diopter base up prisms resulted in subjective vision improvement in primary gaze. There were no limitations in ocular movements, no ocular misalignment, and her visual fields, pupils, external exam, intraocular pressures, slit lamp, and fundus exams were all normal for age.

At that time, we recommended that her neurologist initiate treatment with aminopyridine. She returned to the clinic apparently having not started aminopyridine therapy and continued to have no subjective improvement in her symptoms and no change in her exam. For 6 months, she wore glasses with 10 prism diopters of base up prism bilaterally, reporting improvement in visual function and a decreased chin-down posture. Nevertheless, her nystagmus was unchanged and she strongly desired surgical intervention. A Kestenbaum-Anderson–like procedure involving bilateral superior rectus surgery was discussed with the patient and informed consent was obtained.

The patient underwent uncomplicated bilateral 5.0 mm superior rectus recessions under general anesthesia. Her 1-week postoperative examination showed a marked improvement in head position and very mild elevation deficits in both eyes. At 5 weeks she noted significant functional improvement without oscillopsia or diplopia in primary gaze and no chin-down posture. Uncorrected visual acuities remained stable, ocular ductions were full, and her alignment was orthotropic. On exam she had low-amplitude infrequent beats of downbeat nystagmus in primary position and demonstrated normal head posture. More than 2 years after surgery, the patient reported seeing well without a compensatory head posture but was unavailable for examination.

DISCUSSION

Acquired vertical nystagmus often results in debilitating oscillopsia. Downbeat nystagmus has been studied extensively and a variety of medical treatments now exist, the most promising of which are aminopyridine therapies.¹ However, a significant subset of patients fail to respond to medical treatment, particularly those in whom focal neurologic lesions are the causative factor.² There have been cases of Wernicke encephalopathy with conversion of upbeat nystagmus to permanent downbeat nystagmus that do not respond to medical therapy, which are currently being studied to look into regions associated with nystagmus.^3–5 The nystagmus in the treatment-resistant cases typically dampens in up- or down-gaze, so the potential exists for surgical intervention using a Kestenbaum-Anderson–like operation. There are relatively few reports of adult patients with acquired vertical nystagmus and a compensatory head posture who have had procedures based on the Kestenbaum-Anderson operation.^6–10 These types of muscle procedures have been reviewed,¹¹ and the majority involve children with vertical head tilts and some form of either infantile or acquired nystagmus.^7,8,12,13

The table in the Supplementary Material summarizes all known reported adult patients with acquired vertical nystagmus, including our present case, who have undergone a Kestenbaum-Anderson–like procedure to correct a compensatory head posture. Nineteen of the 25 cases were associated with a clearly defined central nervous system lesion or neurological diagnosis, while the remainder presented as an acquired nystagmus without mention of etiology or causative insult.⁹ That all but two cases had a chin-down head position before surgery is suggestive but not diagnostic of downbeat nystagmus (e.g., Case #1 reported preoperative downbeat nystagmus with a chin-up posture).¹¹ Each of the reported patients showed significant postural improvement after vertical rectus muscle surgery, with only one (#1) having a postoperative compensatory head posture >10°.¹¹ One patient (#2) without preoperative strabismus suffered a postoperative misalignment including a 12° excyclotorsion and four-prism diopter exophoria which improved after bilateral inferior oblique myectomies.¹² Five patients (#8, #9, #15, #16, #17) had additional horizontal rectus surgery to correct preexisting large angle strabismus.¹⁰

Of particular interest was the similarity of our surgical approach to that of Campos et al,⁸ in that we performed a single vertical rectus recession bilaterally. These five patients had minimal postoperative compensatory head posture without the induction of strabismus, indicating that good results may be obtained with surgery on only one muscle per eye.⁸ Hertle and Ahmad also performed bilateral vertical rectus recessions; however, they included bilateral inferior oblique myectomies with all their patients to prevent pattern strabismus or cyclotorsional deviations due to enhanced secondary actions of the inferior oblique muscles.¹⁰ The simpler two-muscle approach to surgical correction of acquired downbeat nystagmus and compensatory head posture, while producing comparable outcomes, has the potential to decrease the complexity of subsequently indicated strabismus surgeries.

Despite variations in data reporting and surgical approaches among the case studies summarized, we can still draw some important conclusions about the utility of a Kestenbaum-Anderson–like procedure in cases of acquired vertical nystagmus. Cyclovertical muscle surgery ought to be considered a viable option in those patients with acquired vertical nystagmus refractory to medical intervention, and the more conservative technique of bilateral single-muscle vertical muscle recessions may be sufficient to provide good outcomes. Based on our review of the literature, we can counsel patients with focal neurologic lesions that do not respond well to medical treatment that there appears to be an opportunity to restore functionality through surgical intervention.

Disclosure statement/Funding

The authors report no funding or conflicts of interest. The patient consented to publication of this report.