Adenocarcinoma metastasis causing discrete extraocular muscle enlargement

Discrete extraocular muscle (EOM) metastasis is rarely reported. Clinical signs and symptoms of EOM metastasis can often be indistinguishable from primary idiopathic orbital myositis, posing a significant clinical challenge. A case of a 61-year-old man with acute-onset unilateral periorbital pain and diplopia is presented. Magnetic resonance imaging showed an isolated edematous superior rectus/levator muscle complex with an isointense T2-weighted signal, supporting a diagnosis of orbital myositis. He was started on corticosteroids, with resolution of pain and improved motilities. Subsequently, his condition worsened. Repeat imaging results suggested the possibility of neoplastic infiltration of the muscle because of the newly demonstrated hyperintensity of the T2-weighted signal and perineural extension along the trigeminal nerve. Fine-needle aspiration biopsy showed adenocarcinoma cytology in the muscle. This case illustrates discrete adenocarcinoma metastasis of an EOM, initially displaying characteristics predominantly consistent with orbital myositis. There is a paucity of epidemiologic data on EOM cancer, and clinical characteristics are derived only from a selection of case reports in the literature. Thus, the predominant features of global orbital metastatic cancer versus primary inflammation are highlighted in this presentation. This case shows that the variable characteristics of each process prohibit identification of any clinical feature that would prove pathognomonic for either disorder. The varied practice philosophies and standard of care regarding the proper time to biopsy are reviewed. This case shows the importance of early referral for orbital biopsy, even in the presentation of isolated, discretely edematous, and painful EOM enlargement.