Endocrine Abstracts

A 43 year old man presented following a seizure. Past history included cranial irradiation 18 years ago for nasopharyngeal carcinoma (NPC). Blood pressure was 100/66 with a postural drop. Examination revealed a bilateral sixth nerve palsy. The only biochemical abnormality on admission was a serum sodium of 117 millimoles per litre. A cranial CT scan was normal.
Further investigation included thyroid stimulating hormone of 3.92 milliunits per litre, a free T4 of 4 picomoles per litre, 9 am cortisol of 326 nanomoles per litre, serum osmolality of 252 milliosmoles per kilogram, urine osmolality of 683 milliosmoles per kilogram, urine sodium of 10 millimoles per litre, testosterone of 9.9 picomoles per litre with non-elevated gonadotrophins. A 250 microgram Synacthen test revealed a baseline cortisol of 87 nanomoles per litre and thirty minute response of 293 nanomoles per litre. Otorhinolaryngeal examination revealed no local tumour recurrence and cranial MRI was unremarkable. A neurologist attributed the cranial nerve palsy to Duane syndrome which is hypoplasia of the abducens nerve nucleus. At follow up, despite optimal hormone replacement he continued to have seizures and was commenced on anticonvulsants.
This case outlines an unusual presentation of hypopituitarism: before investigation we suspected an intra-cranial space occupying lesion complicated by inappropriate anti-diuretic hormone secretion. Hypopituitarism as a result of cranial irradiation is well documented. Studies have shown a 19 percent incidence of pituitary hormone deficiency at 2 years for patients treated for NPC with radiotherapy (1) and a 39 per cent incidence of pituitary deficiency up to 26 years after head and neck irradiation (2). Patients need education about the risk of complications arising many years after the completion of cranial irradiation.
1. Lam K.S. et al. Journal of Clinical Endocrinology and Metabolism(1987)64(3):418-24
2. Samman N.A. et al. International Journal of Radiation Oncology(1982)8(11):1857-67