Primary polydipsia is a clinical disorder characterized by excessive fluid intake (polydipsia) and consequent excessive fluid excretion (polyuria). The underlying pathophysiology of Primary polydipsia is still unclear. We present a case of a 26 year-old man without any previous psychiatric or neurological history who was thoroughly investigated for severe symptoms of polydipsia and polyuria. The only finding consisted of a probable micro-adenoma on the left side of the sella turcica.

The patient was thoroughly assessed by psychiatrists and psychologists through clinical and diagnostic interviews and was administered a wide range of psychometric tools including MMPI-2, SCID, YBOCS, BDI, HAM-17 and SCL-90. Moreover, he underwent a comprehensive physical and neurological examination, blood tests, renal function tests, endocrinological assessment including hormone assays, water deprivation test and desmopressin trial and brain Magnetic Resonance Imaging (MRI).

No major psychiatric disorder was detected apart from the presence of mild depressive symptoms. A brain MRI revealed a 4-5 mm diameter lesion on the left side of the sella turcica with lower contrast enhancement than the rest of the gland, which was suggestive of pituitary micro-adenoma.

We considered the patient's depressive symptomatology as secondary to his condition. There is no other report of pituitary microadenoma in patients with symptoms of polydipsia and polyuria. We hypothesize that the location of the lesion may be related to the hypothalamic centre of thirst.