Endocrine Abstracts

Introduction: Association between lymphoma and pituitary dysfunction is well documented, though most commonly through mechanism of infiltrative pituitary metastasis, or primary lymphoma of the pituitary, rather than autoimmune lymphocytic hypophysitis. Here we present a highly unusual case whereby investigation into the cause of Diabetes Insipidus with radiological features of lymphocytic hypophysitis, led to diagnosis and cure of Diffuse Large B-cell lymphoma (DLBCL). Diabetes Insipidus with an MRI suggestive of autoimmune hypophysitis has been described. However, to our knowledge this is the first case where this presentation has been attributed to a paraneoplastic phenomenon.

Case Presentation: A 67-year-old lady presented to her GP with sudden onset polyuria and polydipsia associated only with a three-day headache. Her GP astutely diagnosed diabetes insipidus. MRI pituitary was highly suggestive of lymphocytic hypophysitis, with enhancement of the pituitary gland, thickening and heterogeneous enhancement of the pituitary stalk, and absence of posterior pituitary lobe T1 hyperintensity. Serum osmolality was 308 mosmol/kg; paired urinary osmolality was 132 mosmol/kg. Anterior pituitary function tests were normal. She experienced complete and instantaneous resolution of symptoms with Desmopressin. Comprehensive investigation into the underlying cause of her clinical and radiological presentation included CT Chest/Abdomen/Pelvis which revealed heterogenous sclerosis of multiple vertebral bodies. MRI whole spine demonstrated widespread bone marrow changes throughout the spine supporting a diagnosis of metastatic disease. Clinical examination remained normal. Myeloma screen and Mammogram were normal. Several attempts at vertebral bone biopsy proved unfruitful. PET-CT demonstrated multi-focal FDG avid sclerotic foci throughout the axial and proximal appendicular skeleton. No primary lesion or organomegaly was identified. Eventually, histopathology from a CT-guided biopsy of the left ilium revealed high-grade Diffuse Large B-Cell Non-Hodgkin Lymphoma of Germinal Centre Cell (GCC) type. She completed 6 cycles of R-CHOP chemotherapy. Subsequent PET-CT showed complete metabolic response.

Discussion: Differential diagnosis of hypophysitis is broad. In this case, we propose that DLBCL presented with paraneoplastic hypophysitis. Alternative serendipitous identification of concurrent DLBCL in a patient with autoimmune lymphocytic hypophysitis is possible. Initial MRI findings were typical of lymphocytic hypophysitis. Interval MRI four months later showed spontaneous regression of stalk changes, prior to lymphoma treatment commencing. Whilst low-grade lymphomas can be associated with waxing and waning phenomenon, this is not the case with CNS lymphoma. Paraneoplastic autoimmune hypophysitis is becoming increasingly recognised. Cases of anti-PIT-1 driven paraneoplastic autoimmune hypophysitis causing anterior pituitary dysfunction have been described. Paraneoplastic posterior pituitary dysfunction may be an emerging area of interest.