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Fabio Bioletto, Marco Barale, Mirko Parasiliti-Caprino, Nunzia Prencipe, Alessandro Maria Berton, Massimo Procopio, Desirée Deandreis, and Ezio Ghigo

Background. Primary hyperparathyroidism is characterized by an autonomous hypersecretion of parathyroid hormone by one or more parathyroid glands. Preoperative localization of the affected gland(s) is of key importance in order to allow minimally invasive surgery. At the moment, 11C-Methionine and 18F-Fluorocholine PET studies appear to be among the most promising second-line localization techniques; their comparative diagnostic performance, however, is still unknown.

Methods. PubMed/Medline and Embase databases were searched up to October 2020 for studies estimating the diagnostic accuracy of 11C-Methionine PET or 18F-Fluorocholine PET for parathyroid localization in patients with primary hyperparathyroidism. Pooled sensitivity and positive predictive value were calculated for each tracer on a “per-lesion” basis and then compared using a random-effect model subgroup analysis.

Results. Twenty-two studies were finally considered in the meta-analysis. Among these, 8 evaluated the diagnostic accuracy of 11C-Methionine and 14 that of 18F-Fluorocholine. No study directly comparing the two tracers was found. The pooled sensitivity of 18F-Fluorocholine was higher than that of 11C-Methionine (92% vs 80%, p < 0.01), while the positive predictive value was similar (95% vs 94%, p = 0.99). These findings were confirmed in multivariable meta-regression models, demonstrating their apparent independence from other possible predictors or confounders at a study level.

Conclusion. This was the first meta-analysis that specifically compared the diagnostic accuracy of 11C-Methionine and 18F-Fluorocholine PET for parathyroid localization in patients with primary hyperparathyroidism. Our results suggested a superior performance of 18F-Fluorocholine in terms of sensitivity, while the two tracers had comparable accuracy in terms of positive predictive value.

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Valentina Gasco, Guglielmo Beccuti, Chiara Baldini, Nunzia Prencipe, Stellina Di Giacomo, Alessandro Berton, Federica Guaraldi, Isabella Tabaro, Mauro Maccario, Ezio Ghigo, and Silvia Grottoli

Objective

Insulin tolerance test (ITT) is the test of reference for the diagnosis of adult GH deficiency (GHD), although GHRH in combination with arginine (ARG) or GH secretagogues are considered equally reliable tests. Testing with GH secretagogue alone is, anyway, a potent stimulus exploring the integrity of hypothalamic pathways controlling somatotropic function. We therefore aimed to determine the diagnostic reliability of testing with ghrelin, the natural GH secretagogue.

Methods

We studied the GH response (every 15 min from −15 to +120 min) to acylated ghrelin (1 μg/kg i.v. at 0 min) in 78 patients with a history of pituitary disease (49 male, 29 female; age (mean±s.d.): 52.1±18.7 years; BMI: 26.7±5.3 kg/m2). The lack of GH response to GHRH+ARG and/or ITT was considered the gold standard for the diagnosis of GHD. The best GH cut-off to ghrelin test, defined as the one with the best sensitivity (SE) and specificity (SP), was identified using the receiver-operating characteristic curve analysis.

Results

The best GH cut-off to ghrelin test was 7.3 μg/l in lean subjects (SE 88.2%, SP 90.9%), 2.9 μg/l in overweight subjects (SE 92.6%, SP 100%) and 0.6 μg/l in obese subjects (SE 50%, SP 100%). The diagnostic accuracy was 89.3, 94.1 and 62.5% respectively.

Conclusions

Our data show that testing with acylated ghrelin represents a reliable diagnostic tool for the diagnosis of adult GHD, in lean and overweight subjects, if appropriate cut-off limits are assumed. Obesity strongly reduces GH response to ghrelin, GH weight-related cut-off limit and diagnostic reliability of the test.