Characterization of pituitary cells targeted by antipituitary antibodies in patients with isolated autoimmune diseases without pituitary insufficiency may help to foresee the kind of future hypopituitarism

Detection of antipituitary antibodies (APA) at high levels and with a particular immunofluorescence pattern in patients with autoimmune polyendocrine syndromes may indicate a possible future autoimmune pituitary involvement. This longitudinal study was aimed at characterizing in patients with a single organ-specific autoimmune disease the pituitary cells targeted by APA at start, verifying whether this characterization allows to foresee the kind of possible subsequent hypopituitarism. Thirty-six APA positive and 40 APA negative patients with isolated autoimmune diseases participated in the study. None of them had pituitary dysfunction at entry. Characterization by four-layer immunofluorescence of pituitary cells targeted by APA in APA positive patients at entry and study of pituitary function in all patients were performed every 6 months during a 5 year follow-up. Antipituitary antibodies immunostained selectively one type of pituitary-secreting cells in 21 patients (58.3 %, group 1), and several types of pituitary cells in the remaining 15 (41.7 %, group 2). All patients in group 1 showed subsequently a pituitary insufficiency, corresponding to the type of cells targeted by APA in 18 of them (85.7 %). Only 8 out of 15 patients in group 2 (53.3 %) showed a hypopituitarism, isolated in 7 and combined in the other one. None of APA negative patients showed hypopituitarism. The characterization of pituitary cells targeted by APA in patients with isolated autoimmune diseases, when the pituitary function is still normal, may help to foresee the kind of subsequent hypopituitarism, especially when APA immunostained selectively only one type of pituitary cells. A careful follow-up of pituitary function in these patients is advisable to allow an early diagnosis of hypopituitarism, even in subclinical phase and a consequent timely replacement therapy.