Progression From Isolated Posterior Pituitary Dysfunction to Combined Anterior Hormone Deficiencies With Pituitary Stalk Enlargement in Suspected Lymphocytic Hypophysitis: A Case Report

Lymphocytic hypophysitis (LYH) is a rare autoimmune inflammatory disorder of the pituitary gland that can involve either the anterior or posterior lobe, or both. In some cases, it initially presents with isolated central diabetes insipidus (CDI) and later progresses to anterior pituitary hormone deficiencies. However, longitudinal descriptions of this progression are limited. A 66-year-old woman presented with dry mouth, polydipsia, and polyuria. Magnetic resonance imaging (MRI) revealed symmetrical pituitary enlargement with loss of the posterior pituitary bright spot, thickening of the pituitary stalk, and homogeneous contrast enhancement of both the pituitary stalk and posterior pituitary. Hormonal testing confirmed preserved anterior pituitary function but impaired vasopressin secretion, consistent with CDI secondary to lymphocytic posterior hypophysitis. During follow-up, serum prolactin levels gradually increased, while cortisol and thyroid hormone levels declined. Approximately one year after the onset of symptoms, MRI showed further pituitary stalk enlargement, and stimulation tests demonstrated diminished responses of adrenocorticotropic hormone, cortisol, and luteinizing hormone. Combined anterior pituitary hormone deficiencies were diagnosed, and replacement therapy with hydrocortisone and levothyroxine was initiated, resulting in symptomatic improvement. Serial hormonal and radiologic assessments revealed the progression from isolated posterior pituitary dysfunction to combined anterior pituitary failure, accompanied by pituitary stalk enlargement. These findings suggest that both mechanical compression resulting from pituitary stalk enlargement and direct inflammatory extension from the posterior pituitary may contribute to the development of anterior pituitary dysfunction. This case was considered to represent LYH, showing possible dynamic changes in pituitary function and morphology over time. Administration of pharmacologic-dose steroids or pituitary biopsy should be considered if further progressive pituitary enlargement or new mass effects, such as headache or visual disturbance, become evident.