ODP541 Burr Under the Saddle: A Case of Sellar Plasmacytoma

BACKGROUND: Sellar and parasellar plasmacytoma is a rare tumor that often poses a diagnostic challenge as it can often be misdiagnosed as a nonfunctioning pituitary adenoma. Here we present a case of sellar plasmacytoma and point to clues helping establish the diagnosis. CLINICAL CASE: 60-year-old male presented with two weeks of worsening morning headache followed by eyelid drooping. A physical exam was notable for left-sided ptosis, mydriasis, poor pupillary light reflex, and otherwise normal eye movement in cardinal positions . Head CT revealed 33×32×30 mm sellar mass; thus endocrinology team was consulted for evaluation. Further workup revealed normal TSH, free T4, ACTH and morning cortisol, FSH, LH, and IGF-1. He had a minimal elevation of prolactin levels at 33 ng/ml after serial dilutions (reference range: 2-17.7 ng/ml). We noticed the patient had an elevated serum protein concentration of 10.6 g/dl (reference range: 6.4-8.3 g/dl) with an albumin level of 4 gm/dl with an elevated gamma gap at 6.6 g/dl, suggestive of elevated gamma globulins. Serum protein electrophoresis showed an M-spike of 3.8 g/dl, and urine was positive for Bence Jones protein. Brain MRI with and without contrast showed homogeneously enhancing mass mainly within the sphenoid sinus extending down to the clivus, isointense on T1, hyperintense on T2 with no diffusion restriction, encasing the left internal carotid artery with intact pituitary and optic chiasm. Transsphenoidal biopsy showed sheets of plasma cells. Immunohistochemistry showed lambda light chain only and negative for kappa light chain. Flow cytometry was positive for CD38, CD138, CD200, and CD56, confirming a diagnosis of plasmacytoma. Fluorescent in situ hybridization was positive for FGFR3-IGH t(4;14) translocation, indicating a higher risk. Otherwise, beta-2-microglobulin, lactate dehydrogenase, and albumin were within normal. Initial management included pulsed dexamethasone of 40 mg for four days, followed by a taper with skull base radiotherapy, a total of 3500 cGy. Ptosis and eye movement gradually improved. The patient was discharged to start bortezomib-based treatment by the oncology team. Clinical lesson: Based on large case series, sellar plasmacytoma often presents as headache (70%), visual changes (77%), and hyperprolactinemia (38%). Imaging shows clinal invasion (74%), cavernous sinus invasion (49%), encasement of the internal carotid artery (17%) [1]. The differential diagnosis for such findings on imaging includes nonfunctioning pituitary adenoma, chordoma, and meningioma. Special attention to gamma gap, urinary, and serum protein electrophoresis can urge to perform a biopsy to prove the diagnosis of plasmacytoma and avoid delay in therapy. Reference: 1. Lee J, Kulubya E, Pressman BD, et al. Sellar, and clival plasmacytomas: case series of 5 patients with systematic review of 65 published cases. Pituitary. 2017;20(3): 381-392. doi: 10.1007/s11102-017-0799-5 Presentation: No date and time listed