Electrolyte Imbalance: A Case of an Atypical Parathyroid Adenoma Causing SIADH

Scott, R. V., Palazzo, F. F., & Rahman, M.

Northwick Park Hospital, North West London NHS Trust.

A seventy-one year old gentleman was referred for investigation of chronic hyponatraemia. Biochemical testing produced results consistent with a syndrome of inappropriate antidiuretic hormone secretion (SIADH). During investigations for an underlying cause, the patient was also found to have hypercalcaemia caused by†† primary hyperparathyroidism.† He underwent a parathyroidectomy with the removal of a large right superior gland. Histology revealed features consistent with an atypical parathyroid adenoma. Following surgery, the patient reported an improved sense of well-being, associated with normocalcaemia and normoPTHaemia. His hyponatraemia had also resolved.† These changes persisted at 6 months, with biochemical resolution of his SIADH.

Hyponatraemia is the most common biochemical abnormality encountered in clinical practice, and SIADH is the most common cause of hyponatraemia.† SIADH is often associated with an underlying tumour, with small cell lung carcinoma being the most common.† As this patientís hyponatraemia resolved following parathyroidiectomy, it is assumed that the parathyroid adenoma was the cause of the SIADH.† Whilst parathyroid adenomas are common within the population, we believe this is the first case report of SIADH being associated with a parathyroid abnormality.†† This shows the importance of looking in unusual sites for malignant and pre-malignant lesions in cases of SIADH if initial investigations fail to reveal an underlying aetiology.†