Introduction: Primary hypothyroidism is most commonly caused by autoimmune hypothyroidism whilst additional causes include post radioactive iodine treatment (RAI) whereas central hypothyroidism is typically associated with pituitary disease. Treatment in primary hypothyroidism aims to maintain the TSH within the reference range whilst treatment of central hypothyroidism is aimed at maintaining free T4 in the upper half of the reference range as established by international guidance. Despite clear guidance patients are at risk of over or under treatment.
Methods: Adults with autoimmune hypothyroidism were identified from a primary care registry whilst those with post RAI or central hypothyroidism were identified from within the relevant outpatient cohorts of Birmingham Heartlands Hospital. Patients were included if they were receiving levothyroxine and had been reviewed by a clinician between October 2016 and September 2017. As such 64 patients with autoimmune hypothyroidism, 63 patients with post RAI hypothyroidism and 38 patients with central hypothyroidism were identified. Their thyroid function tests and any subsequent treatment adjustment were recorded.
Results: Adequate treatment rates were lower than anticipated (25% under treated, 9% over and 66% adequate in autoimmune hypothyroidism; 21% under, 5% over and 74% adequate in the post RAI hypothyroidism; 52% under, 3% over and 45% adequate in the central hypothyroidism group). Dose adjustment in under treated patients occurred variably (14% in the autoimmune hypothyroidism group, 81% in the post-radioiodine hypothyroidism group, and 24% in the central hypothyroidism group).
Conclusion: In this retrospective cohort study, all groups contained patients that were inadequately treated for their hypothyroidism. Under treatment was more common than over treatment and was especially common in patients with central hypothyroidism who despite being reviewed in a specialist centre often did not have appropriate dose adjustment.