We present an unusual case of panhypopituitarism with diabetes insipidus (DI), with diagnostic dilemma despite extensive investigations, and subsequent spontaneous resolution of DI.
A 55-year-old man presented with an abrupt onset of DI (urine output >6L/day, serum sodium 142mmol/L, osmolality 311mOsm, paired urine osmolality 245mmol/L. His GP started DDAVP with dramatic relief. He reported a painless non-dermatomal blistering rash resolving spontaneously after 2 weeks, weight loss (5kg), myalgias and headache but no arthralgias. He was pale, overweight, with good testicular volumes. Biochemically he had profound panhypopituitarism and was started on hydrocortisone and thyroxine with later testosterone replacement. MRI showed a small pituitary gland without posterior bright spot, normal stalk and no intra- or suprasellar lesions but did demonstrate a small frontal lobe lesion with possible ring enhancement. Serum calcium, CSF examination; CT chest/abdomen/pelvis were normal with a negative infectious disease and autoimmune screen. One of three serum ACE was elevated 93U/L (normal<51), though thought insignificant by the respiratory team
Followup MRI (3/12 later) showed a doubling in size of the frontal lesion, with a differential diagnosis of glioblastoma multiforme, lymphoma, and inflammation. Neurosurgical review resulted in commencement of dexamethasone and prompt resection. A firm histopathological diagnosis proved elusive. Histology showed parenchymal necrosis with perivascular, EBV-negative T-lymphocytic infiltrate with monoclonal rearrangement of TCR genes suspicious for peripheral T-cell lymphoma. Despite the clonality, the pattern of infiltration was highly unusual for lymphoma.
High dose steroids were weaned rapidly to physiological replacement. The patient stopped DDAVP without medical supervision. Remarkably, there was no recurrence of polyuria and biochemistry remained normal. Anterior pituitary dysfunction persisted. Sinus node dysfunction was diagnosed after a collapse. A pacemaker was inserted; no evidence of infiltrative disorder was found on cardiac MRI. Indeed, two years later, there has been no definitive evidence of sarcoid, lymphoma or vasculitis.