Deterioration of symptoms after start of thyroid hormone replacement

Case 1

A 26 year old woman with type 1 diabetes, presented with a five week history of lethargy, nausea, feeling lightheaded on standing, occasional vomiting, and four unexplained severe hypoglycaemic episodes. The hypoglycaemic episodes occurred unexpectedly (no change in dietary intake, amount of physical exertion, amount of alcohol ingestion, or dose or timing of insulin therapy).

Thyroid function tests showed a serum concentration of thyroid stimulating hormone of 37.30 mU/l (reference range 0.5-5.7 mU/l) and free thyroxine 12.7 pmol/l (9-22 pmol/l). The patient was started on 25 µg thyroxine daily. This resulted in an immediate exacerbation of symptoms, which prompted a referral to an endocrinologist. On examination she was pigmented and had orthostatic hypotension (92/50 mm Hg supine, 86/60 mm Hg standing). She was hyponatraemic (serum sodium 121 mmol/l) and hyperkalaemic (serum potassium 5.5 mmol/l). Basal serum cortisol was undetectable (<20 nmol/l) and failed to respond to …