Metastatic Atypical Carcinoid Tumor of the Inferior Rectus Muscle

A 74-year-old man who had been treated for pulmonary atypical carcinoid tumor 3 years earlier developed diplopia. Imaging studies showed a well-delineated diffuse enlargement of the right inferior rectus muscle. Downward movement of the right eye was restricted. Incisional biopsy of the affected muscle revealed metastatic atypical carcinoid tumor infiltration that immunostained positively for epithelial membrane antigen, synaptophysin, and chromogranin. Systemic chemotherapy consisting of cisplatin and etoposide was prescribed to address the orbital tumor and a contemporaneously discovered hepatic locus. This treatment provided a 2-year disease-free period with complete resolution of his ocular symptoms. Although metastatic bronchogenic carcinoid tumor in the orbit, and in the inferior rectus muscle in particular, is highly unusual, this condition must be considered in the differential diagnosis of an isolated extraocular muscle enlargement in a patient with a history of systemic carcinoid tumor.