Thyroid eye disease with concurrent orbital lymphoma: a radiological surprise.

Summary: Thyroid eye disease (TED) is the most common extra-thyroidal manifestation in Graves' disease (GD). Additional/concurrent/synchronous pathologies may be present, especially in elderly patients who present with atypical features such as non-axial (or eccentric) proptosis, absence of lid lag and restricted superior extra-ocular movements. A 70-year-old female presented with progressive proptosis of her left eye and diplopia. She was diagnosed with GD a year prior and initiated on carbimazole. On examination, she had eccentric proptosis, restricted superior extra-ocular movements and a palpable mass in the supero-temporal quadrant of the left eye. Her T3 (1.33 ng/mL) and T4 (8.85 µg/dL) were normal with carbimazole. Thyroid-stimulating hormone (TSH)-receptor antibody was positive (3.15 IU/L, reference range <1.75). MRI revealed an enhancing lesion infiltrating the left superior rectus, with concurrent characteristic muscle belly involvement bilaterally. Orbital biopsy showed atypical lymphoid cells (CD20+), suggesting marginal zone lymphoma. CT thorax and abdomen, fluorodeoxyglucose-positron emission tomography and bone marrow examination were normal. The patient was administered orbital radiotherapy for her localised lymphoma and carbimazole was continued. TED is the most common cause of orbital involvement overall and in GD. However, additional or alternative pathology may be present which requires evaluation. MRI can be a useful adjunct in these patients. Orbital lymphoma needs to be staged with workup for disseminated disease. Radiotherapy is the treatment of choice for localized disease. The index case provides evidence for synchronous presentation of dual pathology and highlights the importance of astute clinical examination as well as keeps a low threshold for MRI in selected cases. Learning points: Thyroid eye disease can co-exist with other ocular pathology, especially in elderly individuals. Eccentric proptosis, absent lid lag and restriction of eye movements (suggesting tendon involvement) should alert towards the presence of alternative pathology. Orbital imaging using MRI not only has greater sensitivity in diagnosing radiologically bilateral disease in patients who have unilateral involvement clinically but is also useful to identify concurrent neoplasms.