To report two cases of extraocular muscle enlargement due to malignant cancer metastasis.

A 56-year-old woman presented with horizontal diplopia first noted 1 month earlier. She had a history of small cell lung cancer with brain and bone metastases. She had a -3 abduction deficit in the right eye and esotropia. The forced duction test showed no limitation in horizontal movement. Antibody tests for thyroid disease showed normal results. Brain magnetic resonance image showed multiple nodular enlargements of the right lateral and medial rectus muscles, al so multiple metastatic nodules in the brain. A 38-year-old woman presented with horizontal diplopia first noted 3 months previously. She had undergone breast cancer surgery 6 months earlier. The patient had a -4 abduction deficit in the left eye and esotropia. The forced duction test showed no limitation in horizontal movement. Antibody tests for thyroid disease showed normal results. Orbital magnetic resonance imaging showed nodular enlargement of left lateral rectus muscle including a tendon.

Extraocular muscle metastasis is a possible cause of extraocular enlargement and paralytic strabismus. In a patient with malignant cancer, the physician should consider the possibility of extraocular muscle metastasis and perform imaging for early diagnosis and treatment.