Endocrine Abstracts

Case presentation: This is an 82 year old gentleman who was initially referred to the endocrinology clinic from the oncology team with symptoms of fatigue and postural dizziness with serially low cortisols. His past medical history was significant for metastatic melanoma which had been first diagnosed in June 2024. He underwent treatment with a wide-local excision in August 2024 and was subsequently started on a 12-month course of pembrolizumab from November 2024 onwards. He did not have any other significant medical issues. He remained physically fit and active and regularly cycled around his home city. He had a transient hyperthyroid episode in December 2024 (TSH <0.01 mU/l free T3 12.9 pmol/l free T4 25.5 pmol/l) and he subsequently developed primary hypothyroidism within one month of the initial thyroid function test derangement. He started levothyroxine 75 mg once daily and his TSH subsequently normalised on this dose. In March 2024, he had a 9 am cortisol reading of 64 nmol/l along with multiple low random cortisol levels (81, 86 nmol/l). He was initiated on prednisolone 3 mg once daily for steroid replacement. He was seen by the endocrine nurse for education on emergency hydrocortisone injections and steroid sick day rules. A short synacthen test was carried out in September 2025 and this showed an absent response (cortisol 30 mins 33 nmol/l; 60 mins 40 nmol/l; baseline ACTH <5 ng/l). His eight-hour prednisolone level was 40 ug/l. He had a brief admission to the oncology team with symptoms of general malaise and a large postural drop that corrected with fluids. His investigations did not suggest the presence of any infection. His oncology team doubled his steroids to 6 mg once daily. The patient was keen to remain on the higher dose but we negotiated a compromise of prednisolone 4 mg once daily with the patient in view of his severe fatigue. He had a previous renin level of 0.2 nmol/l/h. We started a small dose of fludrocortisone as an inpatient. He improved clinically after several days and was discharged home. He continues immunotherapy in the outpatient setting with routine endocrinology follow-up.

Discussion points: What are the diagnostic features of immunotherapy-induced adrenal insufficiency? How does immunotherapy affect different parts of the HPA axis? What are the pros and cons of using prednisolone instead of hydrocortisone as steroid replacement? How do you determine whether a patient is receiving adequate steroid replacement? How can renin be used to guide mineralocorticoid replacement in adrenal insufficiency?