Diarrhoea soon after levothyroxine replacement therapy.
Sir,

A 57‐year old woman presented with tiredness, dry skin and weight gain. Examination revealed a smooth goitre with dry greasy skin. Biochemical investigations were consistent with primary hypothyroidism with raised thyroid‐stimulating hormone (TSH) 16.8 mU/l (normal range 0.5–5.5 mU/l) and a low total thyroxine 55 nmol/l (normal range 60–180 nmol/l). Thyroid peroxidase autoantibodies were raised, at a titre of 1:1106 (normal range <1:10); other organ‐specific autoantibodies were not detected and full blood count and electrolytes were normal. 50 mcg of levothyroxine was commenced soon after she become unwell with nausea, vomiting and bloating, associated with watery diarrhoea. She had a normal lactose‐containing diet.

Further investigations revealed a normal cortisol response …