No abstract

Despite the availability of thyroid hormone replacement for more than a century, there are still substantial challenges in practice and opportunities to improve treatment outcomes.

Hypothyroidism is common throughout the world and readily diagnosed with thyroid function tests. Management should be straightforward but appears not to be the case. Thyroid hormone replacement with levothyroxine monotherapy is the standard treatment which is effective in the majority of cases. However, 10–15% of patients established on levothyroxine do not feel their health is entirely restored and some patients prefer the addition of liothyronine. Proponents of liothyronine argue that the ratio of T3 and T4 hormones is substantially altered on T4 monotherapy and therefore both hormones may be needed for optimal health. This remains controversial as clinical trials have not demonstrated superiority of combination therapy (levothyroxine and liothyronine) over levothyroxine monotherapy. There is now a pressing need for further studies and in particular randomized controlled trials in this area. To help design and facilitate dedicated trials and better understand thyroid hormone replacement, this review summarizes the evidence where there is established knowledge and agreement (knowns) and areas where research is lacking (unknowns). Agreements include the extent of dissatisfaction with levothyroxine monotherapy, biases in testing for hypothyroidism and prescribing levothyroxine, as well as variable thresholds for prescribing levothyroxine and challenges in liothyronine dosing. The review will also highlight and summarize the unknowns including the long-term safety profile of liothyronine, and potential biomarkers to identify individuals who might benefit most from combination therapy.

BackgroundSuboptimal thyroid hormone therapy including under-replacement and over-replacement is common amongst patients with hypothyroidism. This is a significant health concern as affected patients are at risk of adverse cardiovascular or metabolic consequences. Despite a growing body of evidence on the effects of various factors on thyroid hormone replacement, a systematic appraisal of the evidence is lacking. This review aims to appraise and quantify the extent to which clinical, behavioural and pharmacogenomic factors affect levothyroxine therapy in patients with primary hypothyroidism.Methods/designThe databases Web of Science, Cochrane Library, EMBASE and PubMed will be searched. Patients must be adults over the age of 18 years, suffering from primary hypothyroidism including overt and subclinical hypothyroidism and receiving levothyroxine treatment. Studies in children, pregnant women and patients with secondary or tertiary hypothyroidism will not be included. We will also exclude studies focused on forms of thyroid hormone replacement therapy other than levothyroxine.The primary outcome is to quantify the effect of clinical, behavioural and pharmacogenomic factors on thyroid stimulating hormone (TSH) levels. Secondary outcomes are the effect these factors have on thyroxine (T4) and triiodothyronine (T3) levels, mortality, morbidity, quality of life, treatment complications, adverse effects, physical and social functioning. Studies will be screened through reading the title, abstract and then full text. Two reviewers will independently extract the data and select articles, and a third reviewer will be consulted if there is any disagreement. We will undertake a meta-analysis of studies in which there is a defined intervention or exposure, patients are receiving levothyroxine for hypothyroidism, there is an appropriate control group of levothyroxine treated patients that are not exposed to the intervention, and the primary outcome is determined by serum TSH levels. Studies will comprise of randomised controlled trials as well as observational data.Eligible studies will be assessed for bias using the risk of bias tool available in the Cochrane handbook 2011, and the quality of evidence will be judged according to the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach. A flow diagram describing the data search will be created according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis: The PRISMA statement. A narrative synthesis will be undertaken in the description of the data, and summary tables will be created of the results.DiscussionThis review will be the first systematic review of this nature. The evidence synthesised will be useful to general practitioners in their management of hypothyroidism. Findings will be disseminated at conferences and in professional and peer-reviewed journals.Systematic review registrationPROSPERO CRD42015027211 Electronic supplementary materialThe online version of this article (doi:10.1186/s13643-017-0457-z) contains ...

Background: Vitamin D deficiency is increasingly recognized in patients with primary hyperparathyroidism but some clinicians are reluctant to replace vitamin D due to concerns with aggravating hypercalcaemia. We investigated the impact of vitamin D repletion in asymptomatic patients with normocalcaemic and hypercalcaemic primary hyperparathyroidism. Methods: This is a retrospective analysis of 111 patients with elevated parathyroid hormone concentrations (>6.4 pmol/L) referred to our endocrine clinic between January and December 2012; we identified 39 patients with primary hyperparathyroidism and vitamin D deficiency, i.e. 25 hydroxy vitamin D <20 mg/L. Patients were categorized into normocalcaemic (n ¼ 23) and hypercalcaemic (n ¼ 16) groups and the impact on biochemical parameters was recorded after at least six months treatment with either 1600 or 3200 units daily of cholecalciferol. Results: Both normocalcaemic and hypercalcaemic groups showed a rise in 25 hydroxy vitamin D concentrations after replacement (p <0.0001). Parathyroid hormone concentrations fell in the normocalcaemic group (p ¼ 0.08) but individually, five patients showed a rise (8-38% of baseline). In the hypercalcaemic group, parathyroid hormone remained static but the adjusted calcium concentration fell significantly (p ¼ 0.006) except in two patients who showed mild rises (3 and 6%, respectively). There was no deterioration in renal function or calcium-related adverse events in any of the groups. Conclusions: Our study supports the safety of vitamin D replacement in patients with mild asymptomatic primary hyperparathyroidism and coexistent vitamin D deficiency. Repletion does not aggravate hypercalcaemia and may limit disease progression. Patients with normocalcaemic primary hyperparathyroidism need further characterization from longitudinal studies.