Pituitary Lymphoma Presenting as Diabetes Insipidus

Introduction: Primary CNS lymphomas are rare accounting for 1-3% of CNS neoplasms. They lack specific clinical or radiological features and are diagnosed histologically. We describe a case of Primary CNS lymphoma involving pituitary gland presenting with confusion and diabetes insipidus. Case: 74-year-old presented with anorexia, weight loss, visual hallucinations and acute confusion. Initial evaluation revealed hypernatremia (148 mmol/L), an old cerebral infarct and new extensive thrombus in aorta and lower limb deep vein thrombosis. During hospital stay, he sustained a fall and a CT head showed a new high attenuation change around the temporal horn and left temporal lobe. MRI head was done to characterize the lesion but because of confusion and irritability, this was inconclusive. Patient continued to have hypernatremia with serum sodium ranging from 148 - 154 mmol/L (135-145 mmol/L) that failed to improve after rehydration. He continued to have negative fluid balance and urine output >2.5 litres a day with dilute urine and urine osmolarity of 134 mosm/L. Due to confusion, we were unable to conduct a water deprivation test. Anterior pituitary profile was consistent with secondary hypothyroidism (TSH was 0.09 (0.02-6.00), Free T4 8.2 (8.0-18.0) and (Free T3 was 2.8 (3.0- 4.8)), and secondary hypogonadism (Testosterone 0.9 nmol/L (6.1-27.1), FSH 1.0 IU/L and LH was <0.2 IU/L). Hypothalamic- adrenal axis was intact as cortisol showed adequate increment after corticotropin stimulation (Cortisol at 0 min 386 nmol/L, 30 minutes 584 nmol/L and 60 minutes 640 nmol/L). Further CT Head with contrast was carried out in view of new findings of hypopituitarism that showed smooth hyperattenuating pituitary gland that was consistent with diabetes insipidus and intense contrast enhancement seen in the periventricular regions and the caudate and dentate nuclei bilaterally. Based on clinical and radiological picture, diagnosis of CNS lymphoma and diabetes insipidus was made and commenced on desmopressin nasal spray. We were unable to perform brain biopsy or quantify the response to desmopressin due to rapid deterioration of patient who died 9 weeks after his initial presentation. An autopsy was carried out and histopathology of pituitary yielded normal anterior pituitary but posterior pituitary was completely infiltrated by Non-Hodgkin’s Lymphoma of Diffuse large B cell type that was also infiltrating parts of the cerebellum, temporal cortex and the basal ganglia hence proving diagnosis of Primary CNS lymphoma. Conclusion: Sudden onset of DI with pathological appearance of posterior pituitary and equivocal/non diagnostic CNS imaging should raise the suspicion of CNS lymphoma. Although diagnosis is histopathological, early detection with high index of suspicion and treatment and lead to better outcomes.