Transient lymphocytic panhypophysitis associated with SIADH leading to diabetes insipidus after glucocorticoid replacement.

A 52-year-old man presented with vomiting, general fatigue and hyponatremia. His symptoms and signs were consistent with the syndrome of inappropriate secretion of antidiuretic hormone (SIADH). Endocrine studies revealed hypopituitarism and administration of hydrocortisone resulted in a marked polyuria. The patient was diagnosed as masked diabetes insipidus. The lymphocytic hypophysitis was also diagnosed on the basis of MRI findings and anti-pituitary antibody. Six months later, these abnormalities disappeared. Diabetes insipidus may exist in a case of hyponatremia due to contrastive SIADH. Such patients may recover spontaneously and careful follow-up is required, avoiding a long-term treatment by monotonous continuation of hormonal replacement.