Isolated levator palpebrae superioris enlargement as the sole harbinger of primary orbital lymphoma.

We report a unique case of 59-year-old man, who presented with a 3-month history of progressive, painless right blepharoptosis with poor levator function. Magnetic resonance imaging demonstrated enlargement of the right levator palpebrae superioris (LPS) with sparing of the superior rectus and other extraocular muscles. The muscle was isointense on T1 and T2-weighted images with homogenous contrast enhancement and a low apparent diffusion coefficient. Incisional biopsy via upper lid skin crease incision revealed a thickened levator muscle, and histopathology showed a low-grade B-cell non-Hodgkin lymphoma with immunophenotype consistent with extranodal marginal zone lymphoma. Systemic staging revealed no extraorbital disease, and therefore, the patient proceeded with localized orbital radiotherapy with resolution at 3-month follow-up. Isolated LPS enlargement with distinct sparing of the superior rectus, presenting as painless ptosis in an orbital lymphoma, is rare. Through this case, the authors highlight the role of diffusion-weighted MRI in single muscle enlargement and provide a brief review of literature.