Background: An abduction deficit can have many potential etiologies. Clinical testing can help distinguish a neurogenic from a restrictive process. For any patient with a current or past history of cancer, even in the setting of vasculopathic risk factors, a further workup is necessary to rule out a metastatic process.
Case report: A 66-year-old man reported sudden blurry vision but did not describe a definite diplopia. Clinical evaluation found left cranial nerve (CN) VI palsy. Although he did have vasculopathic risk factors, neuroimaging found prostate cancer metastasis to the mid to left clivus, extending to the left cavernous sinus region as well as a smaller metastasis to the left temporal lobe. The patient underwent radiation treatment with improvement in his clinical presentation and symptoms. His prostate cancer was subsequently treated more aggressively, and 2 years later, despite spinal metastases, he was doing relatively well.
Conclusion: Prostate cancer commonly metastasizes, with a high propensity to invade bone. CN VI runs along the midline-structured bony clivus, between the pons and the cavernous sinuses. Therefore, a metastatic lesion to the clivus can be responsible for unilateral or bilateral CN VI palsy. In men, a common primary site of cancer metastasis to the clivus is the prostate. Eye doctors must look closely for evidence of even subtle abduction deficits in all patients with a history of prostate cancer. Early detection can lead to improved medical treatment and extended life expectancy.