Endocrine Abstracts

Background: The effect of weight loss on hypothalamic function is complex and not fully understood. There is interplay between neuropeptides (leptin, ghrelin) and hypothalamus with the postulated aim of energy conservation and prevention of pregnancy during unfavourable conditions. We present a memorable case.

Case: A 35-yr-old lady presented with secondary amenorrhoea of 17 years duration. She attained menarche at age 13. At age 16 her periods became scanty and stopped. She had been on the contraceptive pill for 3 years. She never exercised excessively but lost a stone in weight during examination stress as a teenager. She had normal secondary sexual features, weight: 47.9 kg and height: 1.55 m (BMI 19.9).

Investigation and management: After stopping the contraceptive pill her endocrine profile revealed hypogonadotrophic hypogonadism (Oestradiol <37 pmol/L, Luteinising Hormone: 2U/L, Follicle Stimulating Hormone: 5U/L) and mild central hypothyroidism [Thyroid Stimulating Hormone (TSH): 1.35 mU/L, Free thyroxine (FT₄): 10.1 pmol/L]. Bone density scan revealed spinal osteopenia (T-score −2.4) and MRI scan revealed normal pituitary. Because of ongoing tiredness, she had a trial of Levothyroxine 50 mcg daily. Her TSH level fell to 0.02 mU/L while her FT₄ rose above normal (23.8 pmol/L). Upon advice we gradually withdrew the Levothyroxine. Her TSH rose to 0.1 mU/L and FT₄ fell to 18.0 pmol/L on 25 mcg/day of Levothyroxine, and further stabilised (TSH 0.47 mU/L, FT₄ 9.6 pmol/L), six weeks after stopping Levothyroxine. She declined oestrogen replacement because of side-effects but continued calcium-vitamin D supplements. Weight-loss-related hypothalamic dysfunction was discussed. Her weight is currently 50.4 kg and her thyroid function remains stable.

Conclusion: This case highlights the interplay between weight loss and hypothalamic function. The resultant endocrine abnormalities, especially thyroid, could be protective mechanisms and may revert to normal with weight gain. Hasty hormone replacement therapy could make things worse.