Lymphocytic Hypophysitis in a Patient With Suspected Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH)

Lymphocytic hypophysitis (LH) is a rare, autoimmune condition that presents with a range of symptoms that must garner the attention of medical practitioners. Clinically, it is characterized by symptoms of a compressive sellar mass with varying degrees of hypopituitarism due to chronic inflammatory infiltrate of the pituitary gland. It is often seen in women in their third trimester or postpartum and is associated with other autoimmune phenomena. Our case report describes a 73-year-old female with a past medical history of hypothyroidism and hypertension, who presented with continued intermittent dizziness, fatigue, and mild subjective hearing loss for the past several months. She was referred to the emergency department due to a sodium level of 119 and was initially diagnosed with syndrome of inappropriate antidiuretic hormone secretion (SIADH). The patient was treated accordingly; however, she failed to show signs of improvement. Due to her clinical presentation, imaging studies, and laboratory results, the patient was suspected to have LH, which was confirmed with the improvement of her symptoms after treatment with steroids. Because of the rare occurrence and possible atypical presentation of LH, this case illustrates the importance of maintaining a high index of clinical suspicion when diagnosing a patient with an unknown cause of hyponatremia, especially in patients with coexisting autoimmune disorders.