Reversible predominant thyrotropin axis dysfunction with meningitis in suspected lymphocytic hypophysitis.

Lymphocytic hypophysitis (LYH), attributed to autoimmune mechanisms, typically causes multiple anterior pituitary hormone deficiencies, with corticotroph dysfunction occurring earliest; predominant thyrotroph dysfunction is uncommon. A 65-year-old woman presented with headache, fever, and diplopia. Laboratory tests revealed marked systemic inflammation and cerebrospinal fluid (CSF) pleocytosis. Pituitary magnetic resonance imaging (MRI) demonstrated diffuse enlargement and homogeneous contrast enhancement of the pituitary gland and stalk. Endocrinological evaluation showed paradoxically decreased thyroid-stimulating hormone (TSH) despite low thyroid hormone levels, contrasting with elevated adrenocorticotropic hormone (ACTH) levels. Endocrinological stimulation tests revealed a markedly blunted TSH response, with preserved gonadotropin and growth hormone responses, indicating predominant thyrotroph dysfunction despite preserved corticotroph function. Glucocorticoid therapy resulted in prompt improvement of clinical, laboratory, and MRI findings, with complete recovery of anterior pituitary functions. A presumptive diagnosis of LYH with reversible predominant thyrotroph dysfunction and meningitis secondary to direct extension of pituitary inflammation was established. This case demonstrates that LYH can present with atypical anterior pituitary hormone dysfunction, may be complicated by aseptic meningitis, and requires prompt glucocorticoid therapy for favorable outcomes.