We present a 71-year-old gentleman who was referred with a 3-month history of tiredness and proximal myopathy, diarrhoea, rapid weight loss and new onset diabetes mellitus.
On examination, he had features consistent with cortisol excess including thin skin, abdominal striae, proximal muscle wasting and peripheral oedema to his thighs. Neck examination revealed a palpable 2-cm right-sided thyroid nodule.
Laboratory investigations showed hyperglycaemia and hypokalaemia. Endocrine testing confirmed Cushings syndrome caused by ectopic ACTH secretion (ACTH 264.5, NR 046) with the remainder of his pituitary function and pituitary MRI within normal limits. Fine-needle aspiration of the thyroid nodule was consistent with medullary thyroid carcinoma (MTC) and serum calcitonin was 4568 (NR <4.8).
He was commenced on metyrapone to reduce cortisol secretion. CT scanning demonstrated multiple lymph node metastases in his chest and normal adrenal glands. His inpatient stay was complicated by episodes of breathlessness and hypoxia. CTPA showed ground glass changes and atelectasis. Broncho-alveolar lavage revealed Pneumocystis jirovecii and treatment with co-trimoxazole was initiated. Over the course of 3 weeks his condition stabilised and he was fit for surgery. He tested negative for HIV.
He underwent total thyroidectomy with radical neck dissection and his cortisol and ACTH levels improved postoperatively. Histology confirmed MTC as the source of ectopic ACTH.
This case illustrates both an unusual cause of Cushings syndrome and an unusual complication from immunosuppression associated with cortisol excess. Medullary thyroid cancer can secrete ACTH in up to 40% of cases, but rarely causes an ectopic ACTH syndrome. Some degree of immunosupression is a recognised complication of cortisol excess but P. jirovecii infection has been described rarely.