P values should not merely be used to categorize results into significant and non-significant. This practice disregards clinical relevance, confounds non-significance with no effect and underestimates the likelihood of false-positive results. Better than to use the P value as a dichotomizing instrument, the P values and the confidence intervals around effect estimates can be used to put research findings in a context, thereby taking clinical relevance but also uncertainty genuinely into account.
Olaf M Dekkers
Olaf M Dekkers and Rolf H.h. Groenwold
The name of the study should properly reflect the actual conduct and analysis of the study. This short paper provides guidance on how to properly name the study design. The first distinction is between a trial (intervention given to patients to study its effect) and an observational study. For observational studies, it should further be decided whether it is cross-sectional or whether follow-up time is taken into account (cohort or case-control study). The distinction prospective-retrospective has two disadvantages: prospective is often seen as marker of higher quality, which is not necessarily true; there is no unifying definition that makes a proper distinction between retrospective and prospective possible.
Herman Verloop, Johannes W A Smit, and Olaf M Dekkers
Thyroid function abnormalities are common during treatment with tyrosine kinase inhibitors such as sorafenib. Suggested causes are direct effects on thyroid tissue and increased extrathyroidal metabolism of serum thyroxine and 3,5,3-triiodothyronine. We postulated that tyrosine kinase inhibitors may affect the peripheral metabolism of TSH as well. The effect of sorafenib on TSH clearance was studied.
In a study of athyreotic patients on TSH suppression therapy, TSH concentrations were measured after recombinant human TSH (rhTSH) injections before and after 26 weeks of sorafenib therapy.
Before and after the last week of sorafenib therapy, 20 patients with progressive differentiated thyroid carcinoma received a standard dose regimen of two injections 0.9 mg rhTSH on two consecutive days. TSH concentrations were measured 48 h (TSH48 h) and 96 h (TSH96 h) after the first rhTSH injection. The area under the curve (TSH-AUC), reflecting TSH content between 48 and 96 h following rhTSH administration, was calculated.
TSH48 h levels (120.5 mU/l before vs 146.3 mU/l after; P=0.029), TSH96 h levels (22.0 mU/l before vs 35.5 mU/l after; P=0.001), and TSH-AUC (142.7 vs 186.8 mU/l; P=0.001) were significantly higher after sorafenib treatment. Higher sorafenib doses were associated with increased changes in TSH96 h and TSH-AUC. In two patients, TSH levels after sorafenib therapy exceeded 200 mU/l.
Sorafenib therapy is accompanied by higher rhTSH levels, probably due to a decreased TSH clearance. Further studies are recommended to clarify whether a decreased clearance of TSH is sorafenib specific.
Natasha M Appelman-Dijkstra, Marnick Rijndorp, Nienke R Biermasz, Olaf M Dekkers, and Alberto M Pereira
Recombinant human growth hormone (rhGH) replacement is advocated in adult growth hormone-deficient (GHD) patients to increase bone mass and improve lipid profile, body composition, and quality of life. The long-term effects of discontinuation of rhGh replacement are unknown.
This cohort study and systematic review aim to evaluate the long-term metabolic effects of discontinuation of rhGh replacement in adult GHD patients, with a subgroup analyses according to age (< or > 60 years). Data on anthropometry, lipids, glucose, and bone mass density (BMD) were assessed for 3 years after discontinuation.
Cohort study included 64 patients who had discontinued rhGh replacement for >12 months. Fat percentage increased from 31.5±9.5% to 33.8±9.0% (mean difference 2.3, P=0.003). BMI decreased only in subjects <60 years (P=0.014). Glucose, total cholesterol, and LDL-cholesterol levels did not change; however, the percentage of patients on statins increased slightly from 39% to 44%. HDL-C concentration increased only in patients <60 years (mean difference 0.2, P=0.043). Lumbar spine BMD did not change; however, femoral neck BMD and bone turnover markers decreased in subjects <60 years (P=0.001). Systematic review included eight studies (n=166 patients) with a follow-up duration of 6–18 months. Of the eight studies, three qualified as low risk of bias and five as having an intermediate risk of bias. None of the studies reported handling of statins, bisphosphonates, and glucose-lowering medication or excluded patients using these medications.
In this study, discontinuation of rhGh replacement resulted in metabolic changes only in patients <60 years after 3 years. Further research warrants to determine the optimal strategies for (dis)continuation of rhGh replacement in adult patients with GHD.
Esther Donga, Olaf M Dekkers, Eleonora P M Corssmit, and Johannes A Romijn
The aim of this study was to perform a systematic review and meta-analysis on insulin resistance in adult patients with type 1 diabetes mellitus compared to healthy controls, assessed by hyperinsulinemic euglycemic clamp studies.
Design and methods
We conducted a systematic search of publications using PubMed, EMBASE, Web of Science and COCHRANE Library. Hyperinsulinemic euglycemic clamp studies comparing adult patients with type 1 diabetes mellitus to healthy controls were eligible. Primary outcome measures were pooled mean differences of insulin sensitivity of endogenous glucose production (EGP), of glucose uptake and of lipolysis. We estimated mean (standardized) differences and 95% CIs using random effects meta-analysis.
We included 38 publications in this meta-analysis. The weighed mean differences in EGP during hyperinsulinemia between patients and controls was 0.88 (95% CI: 0.47, 1.29) in the basal state and 0.52 (95% CI: 0.09, 0.95) in insulin stimulated conditions, indicating decreased hepatic insulin sensitivity in patients. Insulin sensitivity of glucose uptake was either reported as M value (M), glucose infusion rate (GIR), glucose disposal rate (GDR) or metabolic clearance rate (MCR). Weighed mean differences were similar for M −3.98 (95% CI: −4.68, −3.29) and GIR −4.61 (95% CI: −5.86, −3.53). Weighed mean difference for GDR was −2.43 (95% CI: −3.03, −1.83) and −3.29 (95% CI: −5.37, −1.22) for MCR, indicating decreased peripheral insulin sensitivity in patients. Insulin mediated inhibition of lipolysis was decreased in patients, reflected by increased non-esterified fatty acid levels.
Insulin resistance is a prominent feature of patients with type 1 diabetes mellitus and involves hepatic, peripheral and adipose tissues.
Charlotte Steffensen, Alberto M Pereira, Olaf M Dekkers, and Jens Otto L Jørgensen
Type 2 diabetes (T2D) and Cushing’s syndrome (CS) share clinical characteristics, and several small studies have recorded a high prevalence of hypercortisolism in T2D, which could have therapeutic implications. We aimed to assess the prevalence of endogenous hypercortisolism in T2D patients.
Systematic review and meta-analysis of the literature.
A search was performed in SCOPUS, MEDLINE, and EMBASE for original articles assessing the prevalence of endogenous hypercortisolism and CS in T2D. Data were pooled in a random-effect logistic regression model and reported with 95% confidence intervals (95% CI).
Fourteen articles were included, with a total of 2827 T2D patients. The pooled prevalence of hypercortisolism and CS was 3.4% (95% CI: 1.5–5.9) and 1.4% (95 CI: 0.4–2.9) respectively. The prevalence did not differ between studies of unselected patients and patients selected based on the presence of metabolic features such as obesity or poor glycemic control (P = 0.41 from meta-regression). Imaging in patients with hypercortisolism (n = 102) revealed adrenal tumors and pituitary tumors in 52 and 14% respectively.
Endogenous hypercortisolism is a relatively frequent finding in T2D, which may have therapeutic implications.
Maria Fleseriu, Olaf M Dekkers, and Niki Karavitaki
Patients with pituitary tumours, ensuing hormonal abnormalities and mass effects are usually followed in multidisciplinary pituitary clinics and can represent a management challenge even during the times of non-pandemic. The COVID-19 pandemic has put on hold routine medical care for hundreds of millions of patients around the globe, while many pituitary patients’ evaluations cannot be delayed for too long. Furthermore, the majority of patients with pituitary tumours have co-morbidities potentially impacting the course and management of COVID-19 (e.g. hypopituitarism, diabetes mellitus, hypertension, obesity and cardiovascular disease). Here, we summarize some of the diagnostic and management dilemmas encountered, and provide guidance on safe and as effective as possible delivery of care in the COVID-19 era. We also attempt to address how pituitary services should be remodelled in the event of similar crises, while maintaining or even improving patient outcomes. Regular review of these recommendations and further adjustments are needed, depending on the evolution of the COVID-19 pandemic status. We consider that the utilization of successful models of pituitary multidisciplinary care implemented during the COVID-19 pandemic should continue after the crisis is over by using the valuable and exceptional experience gained during these challenging times.
Rolf H H Groenwold and Olaf M Dekkers
The validity of any biomedical study is potentially affected by measurement error or misclassification. It can affect different variables included in a statistical analysis, such as the exposure, the outcome, and confounders, and can result in an overestimation as well as in an underestimation of the relation under investigation. We discuss various aspects of measurement error and argue that often an in-depth discussion is needed to appropriately assess the quality and validity of a study.
Saskia le Cessie, Jelle J Goeman, and Olaf M Dekkers
Saskia le Cessie, Jelle J Goeman, and Olaf M Dekkers
When statistically comparing outcomes between two groups, researchers have to decide whether to use parametric methods, such as the t-test, or non-parametric methods, like the Mann–Whitney test. In endocrinology, for example, many studies compare hormone levels between groups, or at different points in time. Many papers apply non-parametric tests to compare groups. We will explain that non-parametric tests have clear drawbacks in medical research, and, that’s the good news, they are often not necessary.