An unusual cause of diplopia in a cancer patient.

A 47-year-old woman with metastatic infiltrating lobular carcinoma of the breast developed diplopia. Computed tomography of the orbits showed enlargement and irregularity of the right inferior rectus and inferior obliques muscles. Biopsies of these muscles contained breast carcinoma cells. This case report discusses the causes of diplopia in cancer patients, with special attention to the diagnostic problems of metastasis in extraocular muscles. The possible combined occurrence of metastasis in the leptomeninges and extraocular muscles is also to be borne in mind if the latter diagnosis is not to be missed.