Endocrine Abstracts

Case history: A 37-year-old female presented to her GP with myalgia, lethargy and weight gain. Of note she was 24 months post-partum and had not experienced thyroid problems in either of her two pregnancies. On examination she was overweight with marked myxoedema and proximal myopathy.

Investigations: Serum TSH was greatly elevated at 206 mIU/l and free T4 was undetectable at <3.20 pmol/l. T3 was 2.8 pmol/l. She was referred urgently to the medical team for assessment in A&E where further blood tests demonstrated a raised creatinine at 90 umol/l with an eGFR 61 ml/min and a raised creatinine kinase (CK) at 1018 IU/l. Lipid profile was in keeping with an overt hypothyroidism. Total cholesterol was raised 6.13 mmol/l with normal triglycerides at 1.22 mmol/l, total cholesterol to HDL radio was raised at 5.24, LDL cholesterol was raised at 4.41 mmol/l and non-LDL cholesterol was raised at 5.0 mmol/l. ALT was raised at 63 IU/l. Her ECG was abnormal with a low voltage and flattened T waves with a rate of 75 bpm. An echocardiogram showed a slightly hypokinetic basal inferior wall.

Results and treatment: Thyroid ultrasound showed a hypotrophic thyroid gland with irregular contours with appearances suggestive of thyroiditis sequelae. There was no hypervascularity in doppler mode evidencing no acute thyroiditis. Interestingly, thyroid peroxidase antibodies were negative. TSH receptor antibodies, however, were greatly elevated at > 30.0 u/ml. She was commenced on levothyroxine 125 mcg once daily and within one week of treatment had already noticed an improvement in her energy levels. She will be closely monitored, particularly as literature suggests that there is a risk of transition to hyperthyroidism following treatment with levothyroxine. She will also be screened for other concomitant autoimmune conditions such myasthenia gravis.

Conclusions and discussion: It is rare for autoantibodies to bind to, but not activate, the TSH receptor thereby blocking the action of TSH causing hypothyroidism. TSH receptor blocking antibodies, when present, are generally found to be of a higher titer than TSH receptor stimulating antibodies, as in this case the titer was >30 u/ml. The case also illustrates the importance of checking thyroid function when investigating myalgia. Polymyositis-like syndrome in hypothyroidism is a rare condition characterised by proximal muscle weakness and elevated muscle enzymes. Symptoms usually improve with thyroxine treatment.