In adults, what is the most common cause of acute abducens nerve palsy?

The most common cause of acute abducens nerve palsy in adults is microvascular ischemia. This condition often arises in the context of vascular risk factors such as diabetes and hypertension, which can lead to small vessel disease affecting the nerve's blood supply. Unlike other cranial nerves, the abducens nerve is particularly susceptible to ischemic damage due to its long intracranial course and the vulnerability of the brainstem where it traverses.

Microvascular ischemia manifests as sudden onset of horizontal diplopia, and patients may retain full eye movements in all directions except for abduction of the affected eye. This common etiology generally presents without additional neurological signs, allowing clinicians to distinguish it from palsies caused by structural lesions, such as tumors or hemorrhages, which might involve other neurological deficits as well.

In contrast, trauma is a less frequent cause in the absence of significant head injury, as is idiopathic injury, where the cause remains unknown but typically does not account for the majority of cases. Structural lesions, while they can lead to abducens palsy, are much less common than microvascular issues, especially in the adult population without notable underlying pathology. Therefore, microvascular ischemia is most frequently identified as the cause of acute ab