Hyperthyroidism complicates ~1 in 10002000 pregnancies, with majority of cases due to Graves disease (GD). PTU remains the preferred ATD of choice in pregnancy with carbimazole a reasonable second-line alternative in patients allergic or intolerant to PTU. We present the case of a lady with PTU induced agranulocytosis in pregnancy.
A 29-year-old lady was seen in thyroid clinic in May 2006 having had symptoms suggestive of thyrotoxicosis since December 2005. Her mum had thyrotoxicosis. She was started on carbimazole 30 mg OD. As she had headaches her dose was reduced to 5 mg OD by her GP. Examination in clinic confirmed GD as evidenced by fine tremor, tachycardia (124 bpm), diffuse goitre and mild thyroid eye disease. TFT showed FT4 70.2 pmol/l (N: 1022), FT3 27.3 pmol/l (N: 3.16.8) and TSH <0.1 mIU/l (N: 0.44). Anti-TPO antibody was 29 IU/ml. She was changed to PTU 100 mg TDS as her headaches worsened with carbimazole 30 mg OD. Based on repeat TFT showing FT4 90 pmol/l and TSH<0.01 mIU/l, her PTU was increased to 200 mg TDS. In October 2006, her FT4 normalised to 21 pmol/l and she was booked for Radio-iodine (RAI) in November 2006. Her RAI was abandoned as her urine pregnancy test was +ve on arrival prompting referral to antenatal services. Her TFT (fT4 13.1, fT3 4.3, TSH <0.02) was stable on PTU 350 mg BD. In April 2007, she presented to GP with sore throat and FBC confirmed low neutropil count 0.2×109/l. Her PTU was stopped and she was admitted with close observation over next few days. Her neutrophil count improved steadily and she underwent total thyroidectomy after 2 weeks. Her repeat TFT post-operatively was FT4 16.8 pmol/l and TSH <0.02 mIU/l. She was started on thyroxine and delivered a healthy baby in May 2007.