MON-421 A Case of Central Diabetes Insipidus in a Patient with Myxopapillary Ependymoma and GFAP Paraneoplastic Autoimmune Meningoencephalomyelitis

Background: Glial fibrillary acidic protein (GFAP) specific IgG autoantibody has been identified as a potential biomarker of immunotherapy responsive, sometimes paraneoplastic autoimmune meningoencephalomyelitis. We present one of the first cases of central diabetes insipidus (DI) in a patient with myxopapillary ependymoma and related GFAP paraneoplastic autoimmune meningoencephalomyelitis. Clinical case: A 23 year old female presented with progressive left facial and right sided weakness, extremity parasthesias, diplopia and word finding difficulty over four months. MRI brain showed 3cm left frontal periventricular white matter lesion. Stereotatic brain biopsy revealed a demyelinating process. She was found to be GFAP IgG positive concerning for GFAP astrocytopathy and glucocorticoid treatment was initiated. Four months later, she developed new polydipsia (22L water/day) and polyuria with elevated sodium 151mmol/L, serum osmolality 329 mOsm/kg (normal range 285-310), low urine osmolality 122 mOsm/kg (normal range 300-900), dilute urine specific gravity 1.003 and documented urine output greater than 4L/24hrs. Clinical presentation was consistent with central DI as the patient had an appropriate response to DDAVP administration. MRI pituitary revealed absence of the posterior pituitary bright spot with increased fullness of the posterior aspect of the pituitary gland and prior evidence of pituitary stalk thickening, suggestive of lymphocytic infundibuloneurohypophysitis. Baseline anterior pituitary function remained intact. MRI spine obtained one month later for acute worsening lower extremity weakness, urinary retention and incontinence noted diffuse leptomeningeal enhancement, nodularity and an irregular L2/L3 mass-like lesion. Biopsy confirmed a WHO grade I myxopapillary ependymoma and chemotherapy was initiated. Conclusion: While the underlying etiologies can be identified in approximately 50-70% of central DI cases, the remaining are deemed idiopathic with speculation that autoimmunity involving autoantibodies may be involved. Lymphocytic infundibuloneurohypophysitis has been linked to central DI in several case reports, albeit few. Interestingly, although various autoimmune endocrinopathies have been noted in cases of GFAP autoimmune meningoencephalomyelitis, to our knowledge, this is the first case report of associated central DI.