Endocrine Abstracts

Pineal germinomas account for the majority of intracranial germ cell tumors. Surgery and radiation are usual management options, and secondary hypopituitarism can ensue after both. Diabetes insipidus is particularly common after surgical removal of pineal tumors, but improvement in polyuria and polydipsia years after surgery is exceedingly rare. Here, we present the case of a 49-year-old male, who was diagnosed with a pineal germinoma at the age of 20, which was surgically removed and then irradiated. The patient went without treatment until the age of 30, when he was hospitalized for inaugural diabetic ketoacidosis, and diagnosed with type I diabetes mellitus, as well as secondary panhypopituitarism. Insulin therapy, as well as hormone substitution treatment with levothyroxine, hydrocortisone, testosterone and desmopressin, was immediately started and the doses were adjusted several times during routine follow-up consultations. For the past several years, the patient has been on a steady dose of levothyroxine, prednisone and testosterone undecanoate; as well as desmopressin lyophilisate, with doses between 180 and 240 mg per day. However, recently, the desmopressin dose has been gradually lowered to 120 ug/day, and the patient was admitted for a routine check-up in our Clinic. Upon monitoring fluid ingestion and output, both were around 1 liter/day, so the desmopressin dose was gradually lowered to 30 ug/day, in the evening. One month later, fluid intake and output were roughly 2-2.5L/day under that dose. Because of that, Desmopressin treatment was stopped, and fluid intake and output increased to 4L/day. Upon reintroducing 30 mg Desmopressin daily, those values normalized. Another interesting finding was that the patient’s testosterone levels repeatedly came back high-normal, despite being towards the end of the interval since the testosterone injection. This was interpreted in the context of the patient’s psychiatric medication (Tianeptine, Haloperidol, Carbamazepine), which could alter SHBG levels. SHBG was measured, which came back within normal limits (80.1nmol/l). Serum βHCG levels were also normal (<0.1 mIU/ml), so further evaluation could involve measuring βHCG in CSF to assess for early recurrence. One surprising feature of this case was the sudden decrease in the Desmopressin necessary, after years of being on relatively high doses; so far, the literature has only described two similar cases, without identifying an underlying reason. This underlines the need for long to very long term follow-up in patients with secondary panhypopituitarism, and poses an interesting question for future research – what could be the reason for this suddenly quenched thirst?