Flutter-Like Oscillations: Causes and Treatment

Introduction

Flutter-like oscillations, also known as ocular flutter, is an uncommon and abnormal movement of the eye characterized by rapid to and fro movement of the eye (saccade) in the horizontal plane and occurs at irregular time intervals without an interval between two saccades. The disorder is commonly found in association with cerebellar damage that may arise post infections. Generally, abnormal saccadic movements are seen superposed on normal oculomotor behaviors. The rapid movements are triggered by various events like

• Blinks.

• Optokinetic stimulation (observing moving targets for visual scanning).

• Triggering the normal saccade.

What Is the Pathophysiology of Flutter-Like Oscillations?

The exact pathophysiology of ocular flutter has yet to be discovered. However, it is currently accepted that ocular flutter occurs as a result of disorders in the functioning of oculomotor structures (involved in rapid eye movements) in the brainstem. Oculomotor structures in the brain stem have units that can generate saccadic movements. Saccades are rapid eye movements between two fixed points in a horizontal, vertical, or oblique plane. In normal conditions, saccades help in fixing the gaze toward an object. The neurons involved in saccade generation are

• Excitatory burst neurons.

• Inhibitory burst neurons.

• Omnipause neurons (keeping the excitatory and inhibitory neurons silent).

Earlier, it was believed that flutter-like oscillations of the eyeballs resulted from impaired functions of the omnipause neurons. It stated that omnipause neurons inhibited the burst neurons. However, the hypothesis needed to receive more evidence from lesion studies. Recent studies and research suggest that variations in the positive feedback loops involving the excitatory and inhibitory burst neurons are the most critical factors in an ocular flutter. The adaptive character of the membranes of the neurons was responsible for the post-inhibitory rebound of activities. As a result, a group of excitatory burst neurons will get depolarized, triggering a saccade. The initial saccade will be directed in one particular direction only. After that, the disorders of the inhibitory burst neuron will cause the to and fro movements.

How Is Ocular Flutter Examined?

The flutter-like oscillations can be clearly observed in the clinical examination as they are macroscopically visible. However, micro flutter, otherwise known as microsaccadic ocular flutter, is an uncommon occurrence of flutter-like oscillations and is detected through magnification. The micro flutter will have inter-saccadic intervals, absent in ocular flutter. Patients with the disorder often complain of blurred vision and shimmering vision. Any abnormal eyeball movement resembling flutter-like oscillations is presumed as ocular flutter due to the implication of a missed diagnosis unless proven otherwise.

How to Differentiate Flutter-Like Oscillations From Opsoclonus?

Disorders of the brain stem or cerebellar diseases cause both opsoclonus and ocular flutter. Although both conditions have a common pathophysiology, the clinical presentation is different. The conjugate to and fro motions are strictly restricted in the horizontal plane in flutter-like oscillations. In opsoclonus, irregular to and fro eye movements are observed in horizontal, vertical, and torsional planes.

What Are the Causes of Flutter-Like Oscillations of the Eyeball?

• Ocular flutter is commonly associated with postural body tremors (tremors of the legs on standing) and truncal ataxia (trunk instability usually occurring on sitting). Examining the patient's cerebrospinal fluid showed an increase in the lymphocyte count. Suggesting an infectious origin.

• The most commonly observed cause of ocular flutter is encephalitis associated with viral or post-viral infections and metabolic, toxic, and paraneoplastic disorders. In addition, the post-infectious stages are usually accompanied by myoclonus (sudden jerking of a muscle or a group of muscles), emotional lability, and ataxia (a disorder of balance).

• Though direct serological evidence is absent, flutter-like oscillations have been frequently associated with autoimmune reactions post viral infections like mumps virus, enterovirus, cytomegalovirus, and autoimmune deficiency virus (AIDS).

• Besides viral infections, ocular flutter has been associated with small-cell lung cancer (fast-growing lung cancer caused by smoking) and breast cancer. Some studies also suggest the association of flutter-like oscillations of the eyeball with ganglioside antibodies (anti-GQ1b) which indicates the autoimmune pathology of the disorder.

• On brain imaging, the disorder is not associated with any anatomical lesions in the brain stem. Instead, the clinical symptoms are caused by functional disturbances in the cerebellar regions rather than anatomical disturbances. The ganglioside antibodies attack the antigens in the central nervous system, causing the dysfunction of oculomotor functions.

• In children, 50 % of cases of the ocular flutter are reported to be associated with neuroblastoma. Therefore, it is considered a paraneoplastic manifestation of the underlying malignancy. The paraneoplastic manifestation in adults is small cell lung cancer and breast cancer.

What Are the Treatment Strategies for Flutter-Like Oscillations?

Generally, flutter-like oscillations of the eyeball have a benign course. The disorder has a very rare incidence of occurrence. Therefore, an appropriate treatment regimen has yet to be established. The underlying cause should be treated first. However, the defects associated with motility will persist. In adult patients with paraneoplastic syndrome (a group of disorders triggered by a cancerous tumor), the efficiency of immunotherapy cannot be assessed. Early treatment of underlying cancer accompanied by aggressive immunotherapy is effective in some cases of ocular flutter. Aggressive immunotherapy involves immunoadsorption therapy accompanied by plasma exchange. Responsiveness to immunotherapy depends upon the degree of inflammation. The commonly used medical interventions are

• High doses of intravenous immunoglobulins.

• Plasmapheresis.

• Oral steroids are recommended though they are less effective.

• Anti-epileptic agents like Clonazepam and Gabapentin.

• Thiamine.

• A favorable course of the disease has been reported in many cases after appropriate treatment. However, most of the cases are associated with spontaneous remissions.

Conclusion

Flutter-like oscillations of the eyeball and some oculomotor disorders in general, although an uncommon condition, represents a significant symptomatic presentation of underlying severe paraneoplastic syndrome or post-infectious stages. Though it can be partially or fully resolved, increased alertness is warranted by clinicians for signs of occult malignancies or latent systemic disorders. Whenever patients are presented with saccadic abnormalities like ocular flutters and opsoclonus, the physician should conduct an aggressive examination for the early diagnosis of malignancies.