Growth Hormone–Secreting Pituitary Carcinoma Presenting With Isolated Leptomeningeal Involvement: A Challenging Diagnosis

ABSTRACT Objective: To raise awareness of the clinical presentation of growth hormone (GH)-producing pituitary carcinoma and its unique clinical presentation. Methods: A case report of a GH-secreting pituitary carcinoma with predominant leptomeningeal spread presenting as persistent acromegaly post–macroadenoma excision and radiation therapy. Results: A 39-year-old male, diagnosed with a GH-secreting pituitary macroadenoma with acromegaly 3 years prior, presented with persisting acromegalic phenotypic features with associated diabetes mellitus and hypertension. He had undergone an endoscopic transnasal, transsphenoidal adenoma resection, followed 3 months later by conventional cranial irradiation at another center 2 years prior to his current presentation to us. Serum insulin-like growth factor 1 and post 1-hour 100-g oral glucose administration serum GH levels were 1,198 and 393 ng/mL, respectively. Magnetic resonance imaging of the brain with spine screening revealed an empty sella, diffuse enhancing cordal, posterior fossa and cauda-equina leptomeningeal thickening, suggesting lepto-meningeal spread of a primary neoplastic process. Cytologic examination of cerebrospinal fluid revealed GH-immunopositive malignant cells with pancytokeratin negativity. A diagnosis of GH-secreting pituitary carcinoma with leptomeningeal dissemination was made. He was initiated on intermittent short-acting subcutaneous octreotide and systemic chemotherapy with temozolamide 200 mg/m2 for 5 consecutive days every 28-days and concomitant skull and spine irradiation (total dose of 36 Grays in 20 fractions). His metabolic parameters improved following 3 cycles of chemotherapy. Interval assessment of disease status is awaited prior to the fourth temozolamide cycle. Conclusion: Pituitary carcinomas are rare. Clinico-biochemical presentation being indistinguishable from that of an adenoma, demonstration of metastasis is essential for diagnosis. Isolated leptomeningeal presentation is a unique presentation of GH-secreting pituitary carcinomas. Abbreviations: CSF = cerebrospinal fluid; GH = growth hormone; IGF-1 = insulin-like growth factor 1; MRI = magnetic resonance imaging