Recurrent NET metastatic to the EOMs
C. Biopsy the EOMs
NETs are rare neoplasms that arise in the intestine, pancreas, or lungs and can cause hormone hypersecretory syndromes. NETs most commonly metastasize to the liver, followed by bone and lung1; metastasis to the EOMs is uncommon. Most reports describe unilateral involvement; rarely is there bilateral symmetric enlargement of all muscles as seen in this patient.2,3 Patients may develop proptosis, diplopia, motility limitations, eyelid swelling, and optic disc edema.4 Treatment options include excision, exenteration, radiotherapy, hormonal therapy, and chemotherapy.5
The next best step is EOM biopsy (choice C) to confirm neoplastic involvement and eliminate alternative etiologies such as myositis or orbital inflammatory disease. Thyroid eye disease often shows tendon-sparing EOM enlargement, but given the extent of involvement and negative thyroid serologies, this diagnosis is unlikely (choice A). Furthermore, corticosteroids may affect diagnostic yield and should be avoided prior to biopsy.6 PET/CT imaging (choice B) may identify additional metastases and areas of disease activity more accessible for biopsy, but would not provide tissue diagnosis and is not the next best step. Treatment with octreotide for NET metastases (choice D) is appropriate only after disease recurrence is confirmed.