Case 422 -- Sudden onset of polydipsia and polyuria

Contributed by Manuel Zarandona, MD and Geoffrey Murdoch, MD
Published on line in April 2005


The patient is a man in his 20s who experienced a sudden onset of polydipsia and polyuria. Laboratory testing revealed increased serum osmolality (340 mOsm/kg, reference range 275-299), decreased urine osmolality (40 mOsm/kg, reference range 50-1400), and increased serum sodium (150 mEq/L, reference range 136-146). A water deprivation test demonstrated decrease of serum osmolality into normal range with increased urine osmolality in response to a dose of DDAVP, and so the patient was diagnosed with central diabetes insipidus. The initial MRI scan showed mild thickening of the pituitary stalk.

Over the next several months, the patient developed frequent diffuse headaches and severe fatigue. No fevers or weight loss were noted. Physical examination was entirely normal; no visual field disturbances or focal neurologic deficits were present.

A second MRI scan demonstrated enlargement of the pituitary infundibulum (Figure 1) and a cystic pineal gland lesion (Figure 2). (Two images are presented, as the patient's head was slightly tilted.)

Additional laboratory testing revealed FSH <0.3 mIU/mL (reference range 1-12), LH 0.5 mIU/mL (2-12), free testosterone 16.1 pg/mL (50-210), prolactin 33 ng/mL (0.6-19), free T4 0.6 ng/dL (0.8-2.2), and TSH 0.54 (0.49-4.67). Laboratory testing on CSF was negative for alpha-fetoprotein. CSF beta-hCG was 15 mIU/mL; serum beta-hCG was <2 mIU/mL.


A transsphenoidal biopsy of the pituitary was performed. Intraoperative smear preparations (Figures 3, 4, and 5) demonstrate large, round cells interspersed with small lymphocytes and macrophages. The neoplastic cells have clear cytoplasm, well-defined cytoplasmic borders, and round nuclei. An intraoperative diagnosis was rendered.


The material for permanent sections consisted of three delicate fragments of translucent pink soft tissue.


Images from the permanent sections are shown below (Figures 6 and 7). The tissue consists of abundant lymphocytes, macrophages, and large, round cells with pale eosinophilic cytoplasm with occasional vacuoles, distinct cytoplasmic borders, and round nuclei with prominent round nucleoli.


The neoplastic cells are positive for placental alkaline phosphatase (PLAP, Figure 8) and c-kit (Figure 9). CD68 is negative in the neoplastic cells but highlights abundant macrophages (Figure 10).


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