Endocrine Abstracts

Hypothyroidism is a well-known cause of delayed puberty in children. But in rare instances, hypothyroidism can also be related to isolated menarche. The mechanism remains debatable whilst the overall incidence of the condition remains unknown.

Case Report: 6-year girl presented to children’s emergency with 2 days history of vaginal bleeding. Mum reported her being intolerant to cold, constipated and faltering growth compared to her twin sister. Her skin was cold and clammy and she had a hoarse voice but no breast budding, secondary sexual characters, or goiter. Her weight was on the 25th centile and height between 0.4th and 9th centile. All observations were normal including blood pressure. Investigations confirmed severe primary hypothyroidism [very low Free T4 2.1 pmol/l, with very high thyroid-stimulating hormone (TSH) >100mU/l) and raised Thyroid peroxidase antibody (TPO). Her anterior pituitary functions showed raised prolactin 1840 mg/l, mildly raised follicle-stimulating hormone (FSH) 4.6 IU/ml and normal luteinizing hormones, estradiol and Cortisol. Pelvic ultrasound showed a left ovary containing follicles with a pre-pubertal uterus. Treatment was started with 50 mg of Levothyroxine once daily. A month later her symptoms improved and her thyroid function normalized. Although unclear, one of the proposed mechanisms for isolated menarche in profound hypothyroidism is FSH mimicry by a very high TSH (as both TSH and FSH share the alpha subunit) causes follicular stimulation (1). In the absence of negative feedback from thyroid hormone, there is an increased production of TRH which increases the TSH and prolactin in the pituitary gland. Various case reports linking hypothyroidism and precocious puberty have been published with either elevated gonadotrophins along with the development of secondary sexual characteristics or with delayed bone age (2,3). Our child had no signs of central precocious puberty, only mildly elevated FSH, elevated prolactin and isolated menarche. Interestingly, although asymptomatic her twin sister was also diagnosed with profound hypothyroidism a few weeks later. Hypothyroidism should be considered in a girl not only with delayed puberty but also in girls presenting with short stature and isolated early menarche. Delayed bone age and elevated prolactin and/or gonadotrophins could be other indicators for the diagnosis.