ABSTRACT
We describe a case of unusual ocular movement with features of both the Heimann–Bielshowsky Phenomenon and Ocular Neuromyotonia that might suggest that they share some common pathophysiology or be on a spectrum of abnormal firing of ocular motor cranial nerves. We are the first to propose such a relationship.
KEYWORDS: Heimann-bielschowsky phenomenon, ocular neuromyotonia, monocular, episodic
Introduction
The Heimann-Bielschowsky phenomenon (HBP) is a monocular pendular vertical oscillation secondary to longstanding ipsilateral vision loss. Classically, HBP becomes more apparent on distance fixation and is inhibited by convergence or near fixation. The oscillations vary between 1 and 5 cycles per second and the amplitude ranges from 2–5 degrees to 20–30 degrees.1 The underlying mechanism for the HBP is not well understood.
In contrast, ocular neuromyotonia (ONM) is an acquired ocular motor condition, typically occurring after radiation therapy at the skull base. ONM is characterised by recurrent brief episodes of diplopia secondary to unilateral involuntary spasms of one or more extraocular muscles supplied by a single ocular motor cranial nerve (e.g., the oculomotor, and less commonly the trochlear and/or abducens nerve)2 The spasms of ONM are often described as being triggered by ocular movement in the direction of the involved extraocular muscle/nerve. The pathophysiology of ONM, like HBP, remains ill-defined but may be due to ephaptic transmission.
Materials and methods
Patient-informed consent was obtained for submission of a case report.
Results
A 57-year-old white female with no significant past medical history presented with 2 years of worsening right-sided headaches and worsening vision in the right eye. MRI revealed a sphenoid wing meningioma compressing the optic nerve on the right. The best corrected visual acuity was 20/40 in the right eye (OD) and 20/20 in the left eye (OS). The pupils measured 4 mm in the dark and 2 mm in the light OU with a right relative afferent pupillary defect. Extraocular motility was within normal limits. External and anterior segment examination was normal in both eyes. Fundus exam in OD showed diffuse optic atrophy and OS was normal. A Humphrey Visual Field showed a mean deviation of −5.45 decibels (dB) with an inferior arcuate defect OD and was normal OS. After the subtotal neurosurgical resection of WHO grade 1 meningioma, the patient lost vision to no light perception OD. Serial magnetic resonance imaging (MRI) studies showed a recurrence of the meningioma for which the patient underwent fractionated external beam radiation therapy. Serial MR imaging was stable for the next 7 years. The patient subsequently presented to the neuro-ophthalmology clinic with a new finding of a 25 degree vertical pendular oscillations that had a rate of 2 cycles per second in the right eye.These resembled the HBP, however, the oscillations were transient, lasting approximately 2 min and with intervals of no abnormal movements. Gaze position did not affect the onset, frequency, or severity of the findings. A trial of carbamazepine did not alleviate the physical examination findings in this patient.
Discussion
The present case had features of both ONM and the HBP. Episodic, involuntary muscle spasms that are brought on by prolonged gaze are suggestive of ONM. While these features of ONM were not present in our patient, she had undergone radiation therapy in the parasellar region for a meningioma, which has also been associated with ONM in prior reports.3 Furthermore, oscillations of ONM have a larger amplitude and are transient, analogous to the present case. The presumed mechanism is efferent and possibly from ephaptic transmission. Damage to either the oculomotor or abducens nerve during radiation therapy could result in either organisation of the motor nerves or crosstalk subsequently causing neuronal firing in one nerve to cause stimulation of both nerves. In contrast, the HBP is thought to be associated with a disruption of the central fusional vergence mechanism4 or the monocular visual stabilisation afferent system.5 The present model for HBP supports the Helmholtz theory that there are two independent loci in the brain for each eye and that the mechanisms for vergence and stabilisation of vision are learned. Loss of vision in one eye results in the loss of these learned mechanisms due to the lack of necessity for them.
The HBP is continuous and is not believed to be related to ephaptic transmission or efferent disease. The oscillations of the HBP are pendular, inhibited by convergence and fixation and are associated with monocular vision loss as was seen in the present case. However, in the HBP, the oscillations are smaller in amplitude and continuous rather than being episodic.1 Table 1 compares HBP and ONM, and this case has features of both conditions. It is uncommon for patients with sellar radiation to have vision loss and to our knowledge is the first such case in the English language ophthalmic literature.
Table 1.
Comparison of the HBP and ONM. Bolded are symptoms that were present in the current case
| Heimann–Bielschowsky Phenomenon | Ocular Neuromyotonia |
|---|---|
| ● Involuntary, slow, vertical, pendular oscillations in the amblyopic eye ● Inhibited by convergence and fixation ● Smaller amplitude (typically 2–5 degrees) ● Continuous throughout the day ● Associated with monocular vision loss |
● Involuntary spasmodic muscle firing ● Diplopia is common ● Larger amplitude (typically 25 degrees) ● Episodes are transient ● Associated with prolonged gaze ● Associated with radiation therapy in the parasellar region |
Conclusion
The underlying mechanism for the HBP and OMN is not yet understood. We present a case of a patient with monocular vision loss who underwent radiation therapy and subsequently developed wide-angle pendular oscillations in one eye that were episodic but went away with convergence and fixation. While the HBP and ONM have always been considered as two separate disease entities and have been assumed to have two distinct mechanisms, we hypothesise that the underlying mechanism for both the HBP and ONM is analogous. This case supports our hypothesis as it shows a strong overlap between the features which have been attributed to either the HPB or ONM but not to both in the literature.
Supplementary Material
Supplemental data
Supplemental data for this article can be accessed online at https://doi.org/10.1080/01658107.2019.1648520.
Declaration of interest statement
The authors declare that there are no conflicts of interest. The authors alone are responsible for the writing and content of the article.
References
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